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2020
Nutr J
A case-control study of 350 breast cancer patients and 700 controls in Iran found that women with the healthiest combined lifestyle scores—encompassing diet quality, physical activity, and non-smoking—had a 38% reduced breast cancer risk compared to those with the least healthy scores, with effects particularly pronounced in postmenopausal women who showed a 44% risk reduction. Notably, when examining individual lifestyle components, diet quality (measured by the Healthy Eating Index-2010) emerged as the strongest protective factor with a 46% risk reduction in the highest versus lowest category, while physical activity and smoking individually showed no significant associations. These findings suggest that comprehensive healthy lifestyle patterns—particularly high-quality diet—may substantially reduce breast cancer risk in postmenopausal women, though the lack of association in premenopausal women and the dominance of diet over other factors highlights the need for prospective studies to clarify whether combined lifestyle interventions offer synergistic benefits or whether specific components (like diet) drive most of the protective effect.
2020
Environ Int
A systematic review and dose-response meta-analysis of 10 cohort studies found no clear association between cadmium exposure and breast cancer risk, whether assessed through dietary intake or urinary excretion levels, with all analyses showing non-significant results. Analysis restricted to postmenopausal women also showed no associations, and while data were insufficient to examine potential associations in specific subgroups defined by age, smoking status, or hormone receptor status, the overall evidence does not support cadmium as a breast cancer risk factor. The authors note that available data were too limited to rule out possible associations in selected vulnerable subgroups, highlighting the need for future studies with better exposure assessment and larger sample sizes to detect subgroup-specific effects if they exist.
2020
Eur J Clinic Nutr
A prospective cohort study in the Multiethnic Cohort found no direct associations between four widely-used diet quality indexes—including the Healthy Eating Index 2015, Alternate Healthy Eating Index 2010, alternate Mediterranean diet score, and DASH diet—and breast cancer risk when comparing highest versus lowest quintiles of adherence. However, overweight and obesity were significantly associated with breast cancer incidence, suggesting that diet quality may influence breast cancer risk indirectly through its effects on body weight rather than through direct mechanisms. These findings indicate that the breast cancer prevention benefits of healthy dietary patterns may operate primarily through weight management pathways, highlighting that maintaining healthy body weight through diet—rather than specific dietary patterns per se—may be the critical factor for breast cancer prevention, and underscoring the importance of comprehensive lifestyle interventions that address both diet quality and weight control rather than focusing on dietary patterns alone.
2020
Medicine
A meta-analysis of 6 studies found that exposure to solar ultraviolet (UV) radiation was associated with a 30% reduced breast cancer risk overall, with a dose-response analysis showing a linear protective relationship in women over 40 (14% risk reduction per unit increase in UV exposure). Notably, not tanning and covering the limbs were associated with increased breast cancer risk, while sunscreen use showed no association with risk, suggesting that actual UV skin exposure—rather than ambient UV levels alone—may be the key protective factor. This is the first dose-response meta-analysis demonstrating that higher UV exposure correlates with lower breast cancer risk in a linear fashion among middle-aged and older women, likely through Vitamin D production, though the findings highlight the complex balance between skin cancer risks from excessive UV exposure versus potential breast cancer protection from adequate sun exposure, and the need for further research on how factors like estrogen receptor status, Occupation, and ethnicity modify this relationship.
2020
J Natl Cancer Inst
A prospective study of 146,326 women in the UK Biobank found that maintaining a healthy lifestyle—combining favorable diet, physical activity, healthy weight, limited alcohol, and no smoking—was associated with 22% and 31% reduced breast cancer risk in premenopausal and postmenopausal women respectively, even among women with high genetic risk (top third of polygenic risk score). Importantly, women with high genetic risk who maintained favorable lifestyles still achieved 27-32% risk reductions across menopausal groups, and while high genetic risk doubled breast cancer risk overall, lifestyle factors provided consistent protective benefits regardless of genetic predisposition. These findings demonstrate that genetic risk is not destiny: even women with the highest genetic susceptibility to breast cancer can substantially reduce their risk through modifiable lifestyle factors, supporting the critical importance of population-wide lifestyle interventions for breast cancer prevention and providing hope that women at elevated genetic risk can take meaningful action to lower their cancer risk through behavioral changes.
2020
Int J Cancer
A nested case-control study within a large European cohort of 430 breast cancer cases and 645 controls found that while alcohol consumption was associated with a 17% increased overall breast cancer risk (36% for ER-positive tumors), individual sex hormones showed limited evidence of mediating this relationship except for a weak effect through free estradiol. However, when researchers used a sophisticated statistical approach (partial least squares regression) to create an alcohol-related hormonal signature—characterized by lower SHBG and higher estradiol and testosterone—this hormonal pattern was associated with 25% increased breast cancer risk and mediated approximately 24% of the alcohol-breast cancer association. These findings suggest that alcohol increases breast cancer risk partly through a complex hormonal mechanism involving the interplay of multiple sex hormones rather than through individual hormones alone, providing new mechanistic insight into how alcohol consumption drives breast carcinogenesis in postmenopausal women and supporting recommendations to limit alcohol intake for breast cancer prevention.
2020
Int J Environ Res Public Health
A case-control study of 494 breast cancer patients and 515 healthy women in Poland found that night-shift work was associated with a 161% increased breast cancer risk, even after adjusting for other cancer risk factors including BMI, smoking, reproductive history, age, location, and education. While 51.9% of breast cancer cases had a history of shift work compared to 34.1% of controls (108% increased risk overall), further analysis revealed that only night shifts—not other shift patterns—significantly increased risk, showing a 120% increased risk after adjustment for confounders. Given that Poland has a high percentage of night-shift workers and the dramatically elevated cancer risk observed, the authors call for government action on prophylactic measures and workplace policies to protect this vulnerable population from occupational cancer hazards.
2020
Medicina
A systematic review of 12 studies examining nurses and shift work found that most studies showed an association between breast cancer and consecutive rotating night shifts prolonged over time, with risk increasing particularly during early adulthood and after 5 or more years of working 6 or more consecutive night shifts. The review identified disruption of circadian rhythm and alterations in peripheral clock genes and reproductive hormones as key mechanisms linking night shift work to breast cancer development, with potential roles for melatonin suppression and epigenetic changes including telomere alterations. These findings are particularly concerning given that nursing is a predominantly female profession requiring 24-hour staffing, suggesting the need for workplace policies that limit consecutive night shifts and total years of night work exposure, along with further research to establish definitive causal mechanisms and identify protective strategies for the millions of women working night shifts globally.
2020
Env Health Persp
A systematic review and meta-analysis of 14 studies found that spending one or more hours per day in the sun during summer months was associated with a 16% reduced breast cancer risk compared to less than one hour daily, with similar protective effects observed for both 1-2 hours and more than 2 hours of sun exposure. Sun exposure during adolescence appeared particularly protective (17% risk reduction), while exposure after age 45 showed no significant benefit, and interestingly, ambient UV radiation levels alone were not associated with breast cancer risk. These findings suggest that active sun exposure—likely through Vitamin D production—may offer modest breast cancer protection when obtained regularly during youth and early adulthood, though the results should be balanced against known skin cancer risks from excessive UV exposure.
2020
Eu J Epidemiol
A large prospective study of over 300,000 Chinese women followed for 10 years found no association between moderate soy intake (averaging 9.4 mg/day of soy isoflavones) and breast cancer risk, even when comparing the highest (19.1 mg/day) to lowest (4.5 mg/day) intake groups. However, a meta-analysis combining this study with other prospective cohorts found that each 10 mg/day increase in soy isoflavone intake was associated with a modest 3% reduction in breast cancer risk. These findings suggest that while moderate soy consumption typical of Chinese diets appears safe and not associated with increased breast cancer risk, higher intakes may provide modest protective benefits, contrasting with earlier concerns about soy and breast cancer and supporting the traditional consumption of soy foods as part of a healthy diet.
2020
Breast Cancer Res Treat
A prospective cohort study of 57,654 Swedish women aged 40-74 years found that increased alcohol consumption was associated with a 26% higher breast cancer risk, but importantly, this relationship—and the protective effect of physical activity—was consistent across women regardless of their baseline breast cancer risk level. The study used the Tyrer-Cuzick model to categorize women as below average, average, or above average risk and found that additional risk factors (such as family history, reproductive factors, or breast density) did not modify how alcohol and physical activity affected breast cancer risk. These findings support recommending reduced alcohol consumption and increased physical activity for breast cancer prevention in all women, regardless of their individual risk profile, since the lifestyle benefits apply equally whether a woman is at low, average, or high baseline risk of developing the disease.
2020
Food Chem Tox
This article discusses the harmful impacts of polycyclic aromatic hydrocarbons (PAHs) found in deep-fried foods. It highlights their endocrine-disrupting, genotoxic, and carcinogenic abilities when oils used for deep frying are heated repeatedly or at high temperatures. PAHs disrupt steroidogenic pathways which can lead to hormonal imbalances of estrogen and testosterone causing lower sperm quality, estrogenic effects, and endocrine related disorders. Furthermore, PAHs are linked to increased cancer risks through genotoxicity which can cause mutations in the cell. Organ sites that can be affected by this cancer risk are the breast, prostate, colorectal, renal, and pancreas.
2020
Pharmacol Res
A comprehensive review of 10 studies including over 3.7 million individuals found that people who had ever used oral antibiotics had an 18% increased risk of breast cancer, with the association varying by antibiotic type—penicillin, tetracycline, and nitrofuran antibiotics showed the strongest links. The relationship appeared complex and possibly non-linear, with data hinting at increased risk with moderate antibiotic use but potential protective effects after 35 or more prescriptions, though this finding requires careful interpretation due to study limitations. It remains unclear whether antibiotics directly cause breast cancer or whether the association reflects other factors like underlying infections, immune function changes, or disruption of the gut microbiome, highlighting the need for further research into the mechanisms behind this relationship.
2020
PLOS One
A matched case-control study in Karachi, Pakistan examined 411 women with newly diagnosed breast cancer and 784 cancer-free controls to investigate the relationship between Vitamin D levels, supplementation, sun exposure, and breast cancer risk in a population where both Vitamin D deficiency and breast cancer are prevalent. The study found that women with Vitamin D deficiency (serum levels <20 ng/ml) had a 65% increased risk of breast cancer compared to those with sufficient levels (>30 ng/ml), while women who took Vitamin D supplements in the year prior had a 68% reduced risk of breast cancer. The researchers conclude that Vitamin D deficiency is associated with increased breast cancer risk in Pakistani women, and suggest that maintaining adequate Vitamin D levels through supplementation could be a safe, affordable prevention strategy. This approach may be particularly beneficial for reducing breast cancer incidence and mortality among economically disadvantaged women in Pakistan who face barriers to early detection and treatment, though further research is needed to confirm these findings.
2020
Nutrients
A prospective cohort study of 10,930 Spanish female university graduates in the SUN (“Seguimiento Universidad de Navarra”) project examined whether adherence to the 2018 World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) cancer prevention recommendations was associated with breast cancer risk. The study used an 8-item score measuring compliance with recommendations including body fat, physical activity, consumption of wholegrains/vegetables/fruit/beans, avoidance of fast foods and processed meats, limited sugar-sweetened drinks and alcohol, and breastfeeding. While no significant association was found for overall breast cancer risk, women who scored highest on adherence (>5 points vs. ≤3 points) had a 73% reduced risk of postmenopausal breast cancer after adjusting for other variables. The findings suggest that following multiple WCRF/AICR lifestyle and nutritional recommendations together may significantly reduce postmenopausal breast cancer risk through their combined protective effects.
2020
Cancer Epidemiol Biomark Prev
A large international study of BRCA1 and BRCA2 mutation carriers conducted both retrospective (9,232 carriers) and prospective (3,886 carriers) analyses to examine whether tobacco smoking and alcohol consumption affect breast cancer risk in this high-risk population. The study found that smoking for more than 5 years before a first full-term pregnancy (FFTP) was associated with increased breast cancer risk in both BRCA1 carriers (19-36% increased risk) and BRCA2 carriers (25-30% increased risk) compared to women who never smoked, while other smoking variables and alcohol consumption showed no significant associations. These findings suggest that smoking specifically during the prereproductive years may increase breast cancer risk for BRCA mutation carriers, a finding that requires further investigation given its potential public health importance for this high-risk population. This represents the largest prospective study to date examining these lifestyle risk factors in women with BRCA mutations, who already face substantially elevated lifetime breast cancer risk.
2020
Int J Cancer
A prospective study of 42,012 women in the Sister Study followed participants for an average of 7.6 years and identified 1,536 invasive breast cancer cases to examine the association between meat consumption types and breast cancer risk. The study found that higher red meat consumption was associated with a 23% increased risk of invasive breast cancer (highest vs. lowest quartile), and when total meat consumption was held constant in a substitution model, replacing red meat with poultry reduced breast cancer risk by 28%. No associations were found between cooking practices, heterocyclic amines (carcinogens formed during high-temperature cooking), or heme iron from red meat and breast cancer risk, suggesting the red meat-breast cancer link may operate through other mechanisms. The findings suggest that women could potentially reduce their breast cancer risk by replacing red meat with poultry in their diets, though the biological mechanisms underlying this association require further investigation.
2020
Int J Mol Sci
The gut microbiome—trillions of bacteria living in the digestive tract—appears to influence breast cancer risk, treatment effectiveness, and likelihood of recurrence through its effects on metabolism, hormones, immune function, and brain signaling. While cancer treatments can disrupt the gut microbiome and contribute to negative side effects, research shows that the microbiome can be positively modified through diet, probiotic and prebiotic supplements, and exercise. This review synthesizes current evidence on the gut-breast cancer connection and highlights practical strategies for improving gut health that may lead to better treatment outcomes, fewer side effects, and improved overall wellbeing for breast cancer patients.
2020
Repro Toxicol
A 54-year follow-up study of 102 breast cancer cases and 310 matched controls among 9,300 daughters born 1959-1967 in the Child Health and Development Studies cohort found that high maternal perinatal levels of N-ethyl-perfluorooctane sulfonamido acetic acid (EtFOSAA, a precursor to PFOS) combined with high maternal cholesterol predicted a 3.6-fold increased breast cancer risk in daughters by age 52 (95% CI: 1.1-11.6), while maternal PFOS alone was paradoxically associated with decreased risk. These robust findings—consistent across alternative modeling approaches and independent of other maternal factors—demonstrate that prenatal exposure to specific PFAS compounds during critical developmental windows can influence breast cancer risk decades later, revealing multigenerational health consequences of persistent environmental chemicals. The results emphasize the critical importance of studying internal PFAS doses and chemical mixture exposures during vulnerable early-life periods for breast cancer prevention, particularly as current and future generations face continued ubiquitous exposure to these persistent compounds, though experimental validation and replication in additional epidemiological cohorts are needed to confirm causality and inform prevention strategies.
2020
Environ Res
A systematic review of 100 publications across 56 epidemiologic studies found that research enriched with women at higher baseline breast cancer risk—through family history, early-onset disease, or genetic susceptibility—consistently showed stronger and more frequent associations between environmental chemical exposures and breast cancer compared to average-risk populations. Specifically, 80% of studies enriched with family history or early-onset cases showed significant associations with exposures including PAHs, air pollution, DDT, PCBs, PFAS, metals, personal care products, and occupational chemicals, while 74% of studies examining genetic susceptibility found significant gene-environment interactions for various pollutants in women with variants affecting carcinogen metabolism, DNA repair, and oxidative stress. These findings suggest that the inconsistent evidence for environmental chemicals and breast cancer in the literature may partly stem from studying predominantly average-risk populations who may be less susceptible to environmental carcinogens, highlighting the critical need for future research to focus on high-risk populations and measure exposures during key windows of susceptibility (puberty, pregnancy, menopause) to more accurately capture the role of environmental chemicals in breast cancer development.
2020
Cells
A comprehensive review reveals that imbalanced gut and body microbiomes are linked to nearly all established breast cancer risk factors—including obesity, aging, periodontal disease, alcohol intake, reproductive history, and elevated estrogen levels—suggesting that microbial dysbiosis may itself be an important independent risk factor. The altered bacteria can promote cancer through multiple mechanisms: producing harmful metabolic byproducts, changing how the body processes medications and environmental chemicals, disrupting immune system function, and affecting how well cancer treatments work. These findings suggest that maintaining a healthy microbiome through diet, lifestyle, or therapeutic interventions could potentially reduce breast cancer risk and improve treatment outcomes, representing a promising new frontier in breast cancer prevention and management.
2019
Molecules
A study examined the effects of four common herbicides (MCPA, mesotrione, bifenox, and dichlobenil) on breast cancer cells and found that these pesticides, which can remain as residues in plant-based foods, showed harmful effects on cancer cells at physiological concentrations. The researchers also tested whether traumatic acid (TA), a beneficial natural compound found in food, could counteract the effects of these herbicides when cells were exposed to both together. Results showed that TA, in a concentration-dependent manner, was able to influence and potentially reduce some of the effects of the tested herbicides on certain breast cancer cell lines. This research highlights concerns about herbicide residues in food as potential contributors to cancer risk while also suggesting that naturally occurring food compounds like traumatic acid might help mitigate some pesticide effects, though more research is needed to understand real-world implications.
2019
Int J Cancer
A meta-analysis of three nested case-control studies (CPS-II, EPIC-Italy, and NSHDS) including 1,435 breast cancer cases and 1,433 controls examined whether erythrocyte levels of cadmium and lead—both classified as carcinogens—were associated with breast cancer risk. Cadmium levels showed no association with breast cancer in the CPS-II cohort, inverse associations in the EPIC-Italy and NSHDS cohorts, and an overall inverse trend in the meta-analysis (continuous RR = 0.84; 95% CI 0.69-1.01), while large differences in lead distributions across studies prevented meta-analysis, and no individual study found associations between lead and breast cancer risk. These findings indicate that despite cadmium and lead being established carcinogens with persistent environmental presence and ubiquitous human exposure, circulating levels of these metals in adulthood were not associated with increased breast cancer risk in this large pooled analysis. The unexpected inverse association with cadmium observed in some cohorts requires further investigation to understand potential biological mechanisms or confounding factors.
2019
Environ Int
A systematic review of 342 peer-reviewed articles covering 202 unique chemicals used in consumer products analyzed exposure pathways, functional uses, product applications, exposure routes, and associated health risks, finding that phthalates, bisphenol-A, and polybrominated diphenyl ethers were the most frequently studied chemicals, with frequently reported uses including plasticizers, polymers/monomers, and flame retardants in food contact materials, personal care products, cosmetics, furniture, flooring, and electronics. The analysis revealed that publication volume on chemicals tends to surge following major regulatory changes or exposure incidents rather than before market introduction, indicating a reactive rather than proactive approach to chemical safety assessment. These findings highlight the critical gap between the increasingly diverse array of chemicals used in consumer products and our lagging understanding of their exposure pathways and human health risks, emphasizing the urgent need to develop capacity and mechanisms for identifying health risks prior to chemical releases rather than after exposure incidents or regulatory action, to enable preventive rather than reactive public health protection.
2019
PLOS One
Bisphenol AF (BPAF)—a chemical increasingly used to replace BPA in consumer products—shows even stronger estrogen-like effects than BPA and promotes the growth of estrogen receptor-positive (ER+) breast cancer cells through multiple hormone signaling pathways. Laboratory studies revealed that BPAF stimulates cancer cell proliferation by activating estrogen receptors and upregulating AREG, a growth-promoting gene, with blocking either estrogen receptors or AREG preventing BPAF’s cancer-promoting effects. These findings challenge the assumption that BPA alternatives are safer, demonstrating that BPAF may pose equal or greater breast cancer risks than the chemical it’s replacing, and highlight the urgent need for human studies to assess BPAF’s impact on breast cancer risk before its continued widespread use in products marketed as “BPA-free.”
2019
Environ Int
Advanced glycation end products (AGEs), formed during the processing of foods at high temperatures, act as endocrine disruptors and are linked to various health risks. These compounds accumulate in the body over time, promoting oxidative stress, aging, diabetes, and other degenerative diseases. Processed foods, often convenient and inexpensive, are significant sources of AGEs, contributing to hormonal disruption and potential long-term health effects. Choosing minimally processed, whole foods can help reduce exposure to these harmful compounds and support overall hormonal balance, reinforcing the importance of food quality in maintaining long-term health and well-being.
2019
BMJ
A Mendelian randomization study using UK Biobank data (156,848 women including 7,784 breast cancer cases) and Breast Cancer Association Consortium data (122,977 cases, 105,974 controls) examined causal effects of sleep traits on breast cancer risk using genetic variants associated with chronotype, sleep duration, and insomnia symptoms. Two-sample MR analysis confirmed that morning preference reduced breast cancer risk by 12% per category increase (OR = 0.88; 95% CI: 0.82-0.93) and provided suggestive evidence that each additional hour of sleep duration increased risk by 19% (OR = 1.19; 95% CI: 1.02-1.39) for both ER+ and ER- breast cancer subtypes, with inconsistent evidence for insomnia symptoms. These findings—robust to sensitivity analyses accounting for horizontal pleiotropy—provide genetic evidence that being a “morning person” may protect against breast cancer while longer sleep duration may increase risk, suggesting that circadian rhythm patterns and sleep duration represent modifiable risk factors, though the counterintuitive finding regarding sleep duration requires further investigation given that adequate sleep is generally considered health-protective.
2019
J Expo Sci Environ Epidemiol
This study from a longitudinal cohort of 133 women diagnosed with breast cancer before age 50 and 133 age-matched controls without breast cancer. DDT is stored in adipose tissue, and the authors found that serum DDE (the main metabolite of DDT) was inversely associated with BMI amont women who were cancer-free, but that this association did not hold among women diagnosed with breast cancer before age 50. The authors suggest that early exposure to breast cancer among women exposed to DDT may be due to an uncoupling of the relationship between BMI and serum DDT, and that this may reveal biomarkers of risk through further research.
2019
J Occup Environ Med
This case control study was conducted among Hispanic women agricultural workers who are exposed to pesticides. Chemicals associated with BC risk included organophosphates, organochlorines, and a phthalimide, Captan. The study concluded that agricultural work may be associated with increased BC risk in female Hispanic farm workers.
2019
JAMA Netw Open
A population-based cohort study of over 12 million South Korean youths (ages 0-19) followed from 2006-2015 found that exposure to diagnostic low-dose ionizing radiation was associated with a 64% increased overall cancer incidence, with computed tomography scans specifically showing a 54% increased risk. Among specific cancer types, breast cancer showed a particularly striking 132% increased incidence among exposed individuals, along with thyroid cancer (119% increase), myelodysplasia (148% increase), and other myeloid leukemias (114% increase), with risks remaining significant after adjusting for age and sex. These findings from over 1.2 million exposed children and adolescents who developed 1,444 cancers provide compelling evidence that even low-dose diagnostic radiation during childhood and adolescence—a critical window of susceptibility—substantially increases subsequent cancer risk, underscoring the urgent need for judicious use of radiation-based imaging in young people, adherence to ALARA principles (As Low As Reasonably Achievable), and careful consideration of alternative imaging modalities like ultrasound and MRI that don’t involve ionizing radiation.
2019
Chronobiol Int
A nested case-control study of 39,686 postmenopausal women in the California Teachers Study found that women with a definite evening chronotype (“night owls”) had a 20% increased breast cancer risk compared to definite morning chronotypes (“morning larks”), even after adjusting for established breast cancer risk factors. Importantly, this association was observed in a population without substantial night shift work history, suggesting that chronotype itself—the behavioral manifestation of an individual’s underlying circadian rhythm—may be an independent breast cancer risk factor beyond the effects of occupational circadian disruption. These findings raise the intriguing possibility that evening chronotypes may be more susceptible to environmental circadian disruption from factors like artificial light exposure, social jet lag (mismatch between biological and social timing), or irregular sleep-wake patterns, and warrant further investigation in other non-shift worker populations to confirm whether innate circadian preference represents a novel, modifiable risk factor for breast cancer through behavioral interventions targeting sleep timing and light exposure patterns.
2019
Eur J Clinic Nutr
A meta-analysis of seven observational studies including 319,993 participants found that women consuming the most pro-inflammatory diets (highest DII scores) had a 25% increased breast cancer risk compared to those with the least inflammatory diets, with particularly strong associations observed in postmenopausal women (15% increased risk) and hormone receptor-negative breast cancers (36% increased risk). The association varied by geography, showing dramatically elevated risk in Asian populations (130% increase) and more modest effects in European populations (26% increase), while case-control studies showed stronger associations (68% increase) than cohort studies. These findings reinforce that dietary patterns promoting chronic systemic inflammation—typically characterized by high intake of refined carbohydrates, red/processed meats, and trans fats with low intake of fruits, vegetables, and omega-3 fatty acids—contribute meaningfully to breast cancer risk, supporting dietary interventions focused on anti-inflammatory foods as a practical prevention strategy.
2019
Sci Rep
A Spanish case-control study of 973 breast cancer patients matched with controls found that the relationship between caloric intake and breast cancer risk varied dramatically by menopausal status: premenopausal women consuming 20% or more below their predicted caloric needs had a 64% reduced risk, while postmenopausal women consuming 40% or more above predicted needs had a 181% increased risk. For every 20% increase in relative caloric intake (observed versus predicted based on individual metabolism and activity), hormone receptor-positive and HER2-positive breast cancer risk increased by 13%, with triple-negative tumors showing a 7% increase per 20% caloric excess. These findings suggest that maintaining appropriate caloric intake matched to individual energy needs—and potentially moderate caloric restriction combined with regular physical activity—could be an effective breast cancer prevention strategy, particularly important given the different effects observed in pre- versus postmenopausal women.
2019
Breast Cancer Res Treat
A systematic review and meta-analysis of 11 cohort studies found that a history of stressful life events was associated with an 11% increased risk of breast cancer (pooled risk ratio: 1.11, 95% CI: 1.03-1.19). While the increase is modest, the finding suggests that psychological stress may play a role in breast cancer development and that women who experience significant life stressors could benefit from psychological and counseling services as a potential preventive measure. These results add to growing evidence linking chronic stress exposure to cancer risk and underscore the importance of addressing mental health and stress management as part of comprehensive breast cancer prevention strategies.
2019
Environ Int
A case-control study within the California Teachers Study examined 902 women with invasive breast cancer and 936 controls to assess whether serum levels of polybrominated diphenyl ethers (PBDEs)—common environmental contaminants with endocrine-disrupting properties—are associated with breast cancer risk. Blood samples were analyzed for three prevalent PBDE congeners (BDE-47, BDE-100, and BDE-153), with measurements taken an average of 35 months after cancer diagnosis. The study found no significant association between serum levels of any of the three PBDE congeners and breast cancer risk, even when stratified by menopausal status, tumor characteristics, or body weight. However, the authors note important limitations, including that post-diagnosis blood measurements may not reflect pre-diagnostic or lifetime exposures, and the study lacked information on genetic factors that could influence individual susceptibility.
2019
Int J Env Res Public Health
A French population-based case-control study (CECILE study) of 695 breast cancer cases and 1,055 controls measured plasma levels of organochlorine compounds (OCs)—p,p’-DDE and PCB153—at the time of diagnosis and used a physiologically-based pharmacokinetic (PBPK) model to estimate PCB153 exposure levels during adolescence (ages 11-20), when breast tissue may be particularly susceptible to hormonal disruption. The study found no clear association between measured OC levels at diagnosis and breast cancer risk overall, though there was a trend toward decreasing breast cancer odds ratios with increasing OC levels in women aged 50 and over; similarly, negative associations were observed between breast cancer and estimated adolescent PCB153 exposure levels. The PBPK modeling revealed that women born after 1960 had the highest estimated PCB153 exposures during adolescence (coinciding with peak environmental contamination), while older women had very low adolescent exposures, yet the unexpected negative associations between OC levels and breast cancer risk remained unexplained and may represent study artifacts. Despite these puzzling findings, the study demonstrates that PBPK models can be valuable tools in epidemiological research for back-estimating exposures during critical developmental windows, which could help address important questions about how early-life environmental exposures influence cancer risk decades later.
2019
Sci Rep
A case-control study of 1,050 breast cancer cases and 1,229 controls in which inflammatory markers (C-reactive protein and interleukin-6) were measured in 322 randomly selected case-control pairs examined whether dietary magnesium intake affects breast cancer risk directly and indirectly through inflammation. Higher magnesium intake was associated with 20% lower breast cancer risk (adjusted OR = 0.80; 95% CI: 0.65-0.99), while elevated CRP levels were associated with 43% increased risk (adjusted OR = 1.43; 95% CI: 1.02-2.01), though IL-6 showed no association with breast cancer. Path analysis revealed that dietary magnesium intake reduces breast cancer risk through two pathways: a direct protective effect and an indirect effect by lowering CRP levels, an inflammatory marker. These findings suggest that magnesium’s protective role against breast cancer operates both through anti-inflammatory mechanisms (by reducing systemic inflammation as measured by CRP) and through other direct biological pathways, highlighting the potential importance of adequate dietary magnesium intake for breast cancer prevention and the role of chronic inflammation in breast cancer development.
2019
Breast Cancer Res Treat
A case-control study within the MCC-Spain cohort examined 1,389 invasive breast cancer cases and 1,712 controls aged 20-85 years to investigate domain-specific associations between physical activity and breast cancer risk by menopausal status and molecular subtype. The study found unexpected results: occupational physical activity (OPA) intensity was associated with higher breast cancer risk, particularly for premenopausal women (OR = 1.89 for active/very active vs. sedentary jobs) and ER+/PR+, HER2- tumors (OR = 1.80), while sedentary time ≥6 hours/day increased postmenopausal breast cancer risk by 69%; conversely, moderate-to-high intensity household and recreational physical activity above 1,000 MET·min/week reduced breast cancer risk by 14-33% in both pre- and postmenopausal women. These findings reveal important distinctions between types of physical activity: while leisure-time and household physical activity provide protective benefits against breast cancer, occupational physical activity paradoxically showed positive associations with breast cancer risk—particularly for hormone receptor-positive tumors—which may reflect different biological mechanisms, exposure patterns, or confounding factors associated with Occupation. The study highlights that sitting time is an independent breast cancer risk factor regardless of other physical activity, and the surprising positive association between occupational physical activity and ER+/PR+ breast cancer warrants further investigation to understand underlying mechanisms.
2019
Medicine
A meta-analysis of 10 studies including 8,585 breast cancer cases among 686,305 participants examined the relationship between age at first oral contraceptive (OC) use and breast cancer risk through June 2018. The pooled analysis found a 24% increased breast cancer risk associated with earlier age at first OC use (RR = 1.24; 95% CI: 1.10-1.41), with a significant linear dose-response relationship indicating that younger age at first use was associated with higher breast cancer risk. However, subgroup analyses showed inconsistent results with no statistical significance when restricted to studies from Western countries, lower quality studies, smaller sample sizes, shorter follow-up periods, or when stratified by breast cancer subtypes defined by estrogen receptor (ER), progesterone receptor (PR), or HER2 status. The findings suggest that starting oral contraceptive use at a younger age may increase breast cancer risk in a dose-dependent manner, though this association appears to be influenced by study characteristics and may not differ consistently across hormone receptor-defined breast cancer subtypes, highlighting the need for further research to clarify these relationships and inform contraceptive counseling for young women.
2019
Int Arch Occup Environ Health
A systematic review and meta-analysis of 30 studies (with meta-analyses conducted on 13 studies) examined the association between occupational ethylene oxide (EO) exposure and risk of lympho-hematopoietic cancers (LHC) and breast cancer. The overall pooled meta-relative risk was 1.48 (95% CI: 1.07-2.05) for LHC and 0.97 (95% CI: 0.80-1.18) for breast cancer, with meta-RRs for LHC among EO production workers at 1.46 and sterilization workers at 1.07, neither reaching statistical significance. Notably, a clear temporal trend emerged showing substantially higher LHC risk estimates in earlier studies from the 1980s (meta-RR = 3.87) that progressively declined in more recent decades, with studies from the 2000s and 2010s showing meta-RRs of 1.05 and 1.19 respectively, neither statistically significant. The authors conclude that the most informative and methodologically rigorous epidemiological studies published in recent decades do not support an association between occupational ethylene oxide exposure and increased risk of either lympho-hematopoietic cancers or breast cancer, suggesting that earlier positive findings may have been influenced by methodological limitations, exposure misclassification, or confounding factors that have been better controlled in more recent research.
2019
Eur J Clinic Nutr
A meta-analysis of 23 prospective studies including 41,516 breast cancer cases and 1,171,048 individuals found that higher folate intake was associated with reduced risk of ER-/PR- breast cancer (RR = 0.82; 95% CI: 0.68-0.97), with each 100 μg/day increment decreasing risk by 6% for ER- and 10% for ER-/PR- subtypes. Additionally, high folate intake showed protective effects in premenopausal women (RR = 0.94) and individuals with moderate-to-high alcohol consumption (RR = 0.82), suggesting folate may be particularly beneficial for hormone receptor-negative breast cancers and specific high-risk populations.
2019
Arch Med Res
A case-control study of 101 incident breast cancer cases and 101 matched controls at the Instituto de Seguridad Social del Estado de México y Municipios found that women who worked night shifts had 8.58-fold higher odds of breast cancer compared to those who never worked nights (OR=8.58; 95% CI: 2.19-33.8), while breastfeeding was protective (OR=0.12; 95% CI: 0.02-0.60) and early menarche ≤12 years increased risk (OR=18.58; 95% CI: 2.19-148). Despite the small sample size yielding wide confidence intervals, these findings from Mexican women are consistent with studies from other countries positively associating night shift work with breast cancer risk. The results support the hypothesis that night shift work involving circadian disruption increases breast cancer risk, though the large effect size and wide confidence intervals suggest the need for larger studies with more precise estimates to confirm these associations in Mexican populations.
2019
Environ Pollut
This study investigated how three endocrine-disrupting chemicals (BPA, BBP, and DEHP) affect estrogen receptor alpha (ERα) activity under normal and low-oxygen (hypoxic) conditions in breast and endometrial cancer cells. The researchers found that BPA and BBP activated ERα at specific concentrations, while DEHP did not, but all three chemicals enhanced ERα-mediated gene activity and decreased ERα protein levels under hypoxic conditions. BPA and BBP also affected hypoxia-related factors, decreasing hypoxia-inducible factor-1 activity while increasing VEGF (a blood vessel growth factor) secretion in breast cancer cells, whereas DEHP had different effects. The findings suggest that these endocrine disruptors can alter ERα regulation under low-oxygen conditions, which may influence disease processes since hypoxia is common in tumors and other pathological states.
2018
PLOS One
This study investigated how phthalates affect the growth of normal breast cells (MCF-10A) when grown alongside breast fibroblasts derived from tissue near estrogen receptor (ER) positive and negative breast cancers. The researchers found that only fibroblasts from ER-positive breast cancer tissue significantly stimulated breast cell proliferation, and when these co-cultures were exposed to estrogen or three phthalates (BBP, DBP, DEHP), cell growth increased significantly along with markers of cell division and estrogen receptor expression. The effects of phthalates on normal breast cells were similar to those of estrogen and depended on estrogen receptor activity, suggesting that phthalates act through hormone-mediated pathways. The study concludes that phthalates should be considered potential endocrine disruptors with breast cancer risk implications, even at low concentrations, particularly in the presence of estrogen-responsive tissue.
2018
Mol Cell Endocrinol
A review examining parabens—one of the most widely used preservatives worldwide in foods, cosmetics, and pharmaceuticals—found that these easily absorbed chemicals are classified as endocrine-disrupting chemicals (EDCs) that can disrupt hormonal homeostasis and cause multidirectional health implications affecting body fitness and function. The review summarizes current literature on paraben properties, occurrence, metabolism, and particularly their influence on the human endocrine system, emphasizing the importance of assessing their safety given their ubiquitous use and absorption. With parabens now recognized as EDCs capable of disrupting endocrine function, the authors highlight concerns about widespread population exposure through everyday consumer products and the need for precise assessment of their health impacts on human physiology.
2018
Food Chem Tox
A systematic review of 25 studies examining phthalates (plastic chemicals) and breast cancer found that while laboratory studies show certain phthalates can activate estrogen receptors and promote cancer cell growth, epidemiological studies in humans have produced mixed and inconclusive results. The main source of phthalate exposure is through diet—particularly from food and beverages in plastic packaging—but current human studies have significant limitations in how they measure exposure and account for other risk factors. The review calls for better-designed future studies that use hair samples instead of urine for more accurate long-term exposure assessment, include dietary factors and genetic markers as confounders, and investigate phthalates’ effects beyond just estrogen-driven cancers to include all breast cancer subtypes.
2018
PLOS One
A case-control study of 399 breast cancer patients with receptor status information and 324 controls found that current menopausal hormone therapy (MHT) use was associated with approximately double the risk of hormone receptor-positive breast cancers, including ER+ (104% increased risk), ER+/PR+ (129% increased risk), and notably ER+/PR+/HER2- subtypes (130% increased risk). Past MHT use showed no elevated risk for any subtype, and current use was not significantly associated with hormone receptor-negative cancers, indicating the effect is specific to hormonally-driven tumors. These findings provide mounting evidence that MHT specifically increases risk of the ER+/PR+/HER2- subtype—the most common breast cancer type—adding to concerns about current hormone therapy use and supporting the need for women and clinicians to carefully weigh the duration of MHT treatment against cardiovascular and quality-of-life benefits versus breast cancer risks.
2018
Breast Cancer Res
A pooled analysis of three population-based case-control studies including 6,320 women (3,934 cases, 2,386 controls) aged 35-64 years examined whether the associations between body mass index (BMI) and breast cancer risk differ by tumor subtype defined by estrogen receptor (ER), progesterone receptor (PR), and HER2 status. Higher BMI at age 18 was inversely associated with premenopausal breast cancer risk across all ER/PR/HER2 subtypes (≥25 vs. <20 kg/m²: OR=0.72), with the strongest protection seen in premenopausal women who had high BMI both at age 18 and currently (46% reduced risk; OR=0.54; 95% CI: 0.38-0.78), while no significant associations were found for postmenopausal breast cancer. The findings indicate that high BMI during late adolescence provides similar protective effects against all molecular subtypes of premenopausal breast cancer regardless of hormone receptor or HER2 status, and this protection appears to be maximized when women maintain higher BMI consistently throughout their premenopausal years. These results suggest that the mechanisms by which adiposity protects against premenopausal breast cancer operate broadly across different tumor subtypes rather than being specific to hormone receptor-positive disease.
2018
Environ Res
A systematic review of 158 studies examining environmental chemicals and breast cancer found the strongest evidence for increased risk from exposures during critical developmental periods (in utero, adolescence, pregnancy) to DDT, dioxins, PFOSA, air pollution, and occupational solvents, with risk estimates ranging from 1.4 to 5 times higher. A landmark 50-year study that captured DDT exposure during windows of breast development showed particularly elevated risks, while research on genetic variations found that women with certain DNA repair gene variants had higher breast cancer risk from PAH (polycyclic aromatic hydrocarbon) exposure. However, most studies failed to assess exposure timing during biologically relevant windows of susceptibility, and many current-use chemicals in consumer products remain inadequately studied, with major challenges including reconstructing decades-old exposures and measuring rapidly metabolized chemicals in complex real-world mixtures.
2018
BMC Pub Health
A mixed ecological and case-control study in Australia found that obesity occurring between ages 31-40 was independently associated with a 250% increased breast cancer risk in middle-aged women, though no direct association was found between alcohol consumption and breast cancer in the case-control analysis despite ecological correlations. The study revealed that stress was ecologically linked to both alcohol consumption and obesity but not directly to breast cancer incidence, suggesting that stress may influence breast cancer risk indirectly through health behaviors rather than representing a “missing link” as hypothesized. These findings highlight a critical window for breast cancer prevention: obesity in the decade before age 40 appears particularly risky, supporting targeted weight management interventions for women in their 30s, while the complex interrelationships between stress, alcohol, obesity, and breast cancer warrant further investigation using longitudinal designs that can capture temporal sequences and cumulative exposures across women’s reproductive years.