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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
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
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
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
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 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
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
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
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.
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 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
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
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
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
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
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
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
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 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
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
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
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.
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
Breast Cancer Res Treat
A meta-analysis of 25 epidemiological studies (23 cohort studies and 2 randomized trials) found that hormone replacement therapy (HRT) was associated with a 33% increased breast cancer risk overall, with combined estrogen-progestin therapy (EPT) showing stronger associations than estrogen-only therapy (ET). EPT was associated with both ductal (51% increased risk) and lobular breast cancer (38% increased risk), and all HRT types were linked to ER-positive but not ER-negative breast cancers, consistent with hormone-driven carcinogenesis. Notably, Asian women using HRT showed higher breast cancer risk than Western women, possibly due to differences in baseline hormone levels, genetic susceptibility, body composition, or HRT formulations used—a finding highlighting the importance of considering racial and ethnic differences when counseling women about menopausal hormone therapy risks and benefits.
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.
Dietary Inflammatory Potential Score and Risk of Breast Cancer: Systematic Review and Meta-analysis.
2018
Clinic Breast Cancer
A systematic review and meta-analysis of 9 studies including 296,102 participants found that higher dietary inflammatory potential was associated with a 14% increased breast cancer risk overall, though the association varied by study design with case-control studies showing stronger effects (63% increased risk, not statistically significant) than cohort studies (4% increased risk, not significant). The pooled analysis across all study types showed a significant positive association between pro-inflammatory diets and breast cancer, suggesting that dietary modifications to reduce inflammatory potential could meaningfully reduce breast cancer risk. These findings reinforce that chronic low-grade inflammation driven by diet—characterized by high intake of refined carbohydrates, red and processed meats, and trans fats with low consumption of anti-inflammatory foods like fruits, vegetables, whole grains, and omega-3 fatty acids—contributes to breast carcinogenesis, supporting dietary pattern interventions focused on anti-inflammatory foods as an accessible and modifiable prevention strategy for women.
2018
Cancer Epidemiol Biomark Prev
A systematic review and meta-analysis of 24 studies found suggestive evidence that physical activity may reduce breast cancer risk through increased global DNA methylation, with higher activity levels showing a trend toward higher methylation (19% standardized mean difference) and higher methylation associated with a 30% reduced breast cancer risk, though neither association reached statistical significance overall. Subgroup analyses revealed that the protective pathway became clearer when examining long-term physical activity patterns and prospective cohort studies specifically, where both associations were statistically significant. This is the first systematic review to examine the complete biological pathway linking physical activity to breast cancer prevention through epigenetic mechanisms, suggesting that exercise may alter DNA methylation patterns in ways that protect against cancer development—a finding that could help explain how physical activity exerts its well-established cancer-preventive effects at the molecular level.
2018
Eur J Public Health
A 34-year study in Italy’s Veneto Region, where drinking water was contaminated with PFAS chemicals from a manufacturing plant operating since 1964, found significantly higher mortality rates in contaminated communities compared to uncontaminated areas for multiple diseases including diabetes, heart disease, stroke, Alzheimer’s, and breast cancer in women. Women in PFAS-contaminated areas showed elevated mortality from kidney cancer, breast cancer, and Parkinson’s disease, while both men and women had increased deaths from cardiovascular and metabolic diseases. These population-level findings suggest PFAS exposure—from widespread “forever chemicals” used in nonstick cookware, food packaging, stain-resistant fabrics, and firefighting foam—may increase risks for multiple serious diseases including breast cancer, though individual-level studies are needed to confirm causal relationships and understand the mechanisms behind these health impacts.
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.
2018
Nutr Cancer
A case-control study of 136 breast cancer patients and 272 controls in Iran found that women consuming the most pro-inflammatory diets (highest quartile of DII scores) had a 164% increased breast cancer risk compared to those with the least inflammatory diets, with the association particularly striking among premenopausal women who showed a 451% increased risk. No association was detected in postmenopausal women, contrasting with findings from other studies that have typically shown stronger effects in postmenopausal populations. These findings suggest that pro-inflammatory dietary patterns may be especially harmful during premenopausal years when breast tissue is more metabolically active and hormone-responsive, highlighting the potential importance of anti-inflammatory dietary interventions—emphasizing whole grains, fruits, vegetables, legumes, nuts, and fish while limiting processed foods, red meat, and refined carbohydrates—as a targeted prevention strategy for younger women at risk of breast cancer.
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
Int J Cancer
A population-based case-control study in Spain (2008-2013) including 621 prostate cancer cases, 1,205 breast cancer cases, and 2,193 controls who never worked night shifts examined whether meal timing is associated with cancer risk while accounting for lifestyle factors and chronotype (morning vs. evening preference). Participants who waited two or more hours between supper and sleep had a 20% reduced risk of breast and prostate cancer combined (OR = 0.80; 95% CI: 0.67-0.96) compared to those sleeping immediately after eating, with individual reductions of 26% for prostate cancer and 16% for breast cancer; similarly, eating supper before 9 pm versus after 10 pm showed protective effects, with stronger associations among those adhering to cancer prevention recommendations (OR = 0.65) and morning chronotypes (OR = 0.66). These findings suggest that adhering to diurnal eating patterns—particularly maintaining a long interval between the last meal and sleep—is associated with lower breast and prostate cancer risk, independent of diet quality and other lifestyle factors. The study highlights the emerging importance of meal timing and circadian rhythm alignment in cancer prevention, indicating that when we eat may be as important as what we eat, and suggesting that late-night eating close to bedtime may disrupt metabolic and hormonal processes that influence cancer development.
2018
Psycho-Oncology
A prospective cohort study of 2,739 women from 990 Australasian families at increased familial breast cancer risk followed participants over multiple 3-year assessment periods, measuring acute and chronic life stressors, social support, and personality characteristics (optimism, anger control, antiemotionality) to determine their association with breast cancer development. During follow-up, 103 women were diagnosed with breast cancer, but Cox proportional hazard regression analysis found no significant associations between any stressor or psychosocial variable and breast cancer risk in either unadjusted or adjusted models (total acute stressors HR = 1.03, p = .19; total chronic stressors HR = 1.0, p = .98). The study concludes that stress, social support, and personality characteristics do not appear to influence breast cancer risk, even in women with increased familial susceptibility. The researchers emphasize that women should focus their prevention efforts on evidence-based risk reduction strategies rather than worrying about stress or personality factors as contributors to breast cancer development, addressing a longstanding concern about the potential role of psychological factors in cancer development.
2018
Environ Health
A nested case-control study within the California Teachers Study examined 902 women with invasive breast cancer and 858 controls who provided blood samples an average of 35 months after case diagnosis to assess whether serum concentrations of six per- and poly-fluoroalkyl substances (PFASs)—PFOA, PFNA, PFUnDA, PFHxS, PFOS, and MeFOSAA—were associated with breast cancer risk. For all invasive breast cancers combined, none of the adjusted odds ratios were statistically significant, though marginally significant inverse associations were observed for PFUnDA and PFHxS; statistically significant inverse associations for these two compounds were found only among the 107 women with hormone receptor-negative tumors, not among the 743 with hormone-positive tumors. The authors conclude that the study provides no evidence that post-diagnosis serum PFAS levels are related to breast cancer risk, and suggest that the few inverse associations observed may be due to chance or study design artifacts, particularly because measurements were taken after diagnosis rather than before. Future research should include pre-diagnosis PFAS measurements, genetic susceptibility factors, and endogenous estrogen levels to better assess whether these widely used synthetic chemicals—some of which are known mammary toxicants and endocrine disruptors—influence breast cancer development.
2018
Eur J Obstet Gynecol Repod Biol
A hospital-based case-control study of 134 breast cancer cases and 267 controls in Tehran, Iran used a 168-item food frequency questionnaire and factor analysis to identify two major dietary patterns and assess their association with breast cancer risk. The “healthy” pattern (high in fruits, vegetables, seeds, legumes, fish, whole grains, and liquid/olive oils, with low salt) showed no significant association with breast cancer (OR: 0.83), while the “unhealthy” pattern (high in sweets, soft drinks, mayonnaise, solid oils, processed meat, fried/boiled potatoes, and salt) was associated with significantly increased breast cancer risk in the highest versus lowest quartile (OR: 2.21; 95% CI: 1.04-4.69). When stratified by menopausal status, the unhealthy dietary pattern showed a particularly strong association with breast cancer risk among postmenopausal women (OR: 3.56; 95% CI: 1.16-10.95), but not premenopausal women. These findings suggest that overall dietary patterns—rather than individual nutrients or foods—may be important determinants of breast cancer risk, with an unhealthy Western-style diet pattern characterized by processed foods, added sugars, unhealthy fats, and high salt intake potentially more than doubling breast cancer risk, especially in postmenopausal Iranian women.
2018
Maturitas
A Spanish population-based case-control study of 1,006 breast cancer cases and 1,370 controls found that high total meat intake was associated with a 39% increased breast cancer risk in postmenopausal women, with processed/cured meat showing a 47% increased risk overall and a striking 152% increased risk specifically for triple-negative breast cancers. Cooking methods and doneness preferences significantly modified risk: well-done red meat was associated with 62% increased risk and stewed red meat with 49% increased risk (particularly for hormone receptor-positive tumors), while pan-fried or breaded white meat showed 38% increased overall risk and 78% increased risk in premenopausal women. These findings suggest that breast cancer risk could be reduced not only by limiting meat consumption—especially processed meats—but also by modifying cooking practices to avoid well-done or high-temperature cooking methods that generate carcinogenic compounds like heterocyclic amines and polycyclic aromatic hydrocarbons.
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
Biomed Res Int
A case-control study of 116 women with newly diagnosed breast cancer and 226 controls used dual-energy X-ray absorptiometry to examine the relationship between body composition, physical activity, and breast cancer risk, analyzing results separately by menopausal status. In premenopausal women, higher total body fat percentage, android (abdominal) fat, and waist circumference were associated with increased breast cancer risk, while higher lean body mass and greater physical activity were protective; among postmenopausal women, physical activity reduced breast cancer risk by 49%. The study concludes that low lean body mass and high abdominal fat increase breast cancer risk in premenopausal women, while regular physical activity is protective against breast cancer in both pre- and postmenopausal women. These findings suggest that maintaining healthy body composition through physical activity may be an important breast cancer prevention strategy across all life stages.
2018
Breast Cancer Res Treat
A study of 27,153 postmenopausal women in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial created an estrogen-related lifestyle score (ERLS) combining four factors: estrogenic diet, alcohol intake, body mass index (BMI), and physical activity, with scores ranging from 0-6 and higher scores representing lower estrogenic lifestyle patterns. Women with ERLS scores of 4 or ≥5 had 23% and 34% lower breast cancer risk, respectively, compared to those with scores ≤2, with similar protective effects observed for invasive cases and estrogen receptor-positive subtypes. The findings indicate that adopting multiple low-estrogen lifestyle behaviors together—including a low estrogenic diet, minimal alcohol consumption, healthy body weight, and high physical activity—has a combined protective effect against postmenopausal breast cancer that is stronger than any single factor alone. The researchers suggest this combined effect likely works by influencing estrogen metabolism, highlighting the importance of addressing multiple lifestyle factors simultaneously for breast cancer prevention in postmenopausal women.
2022
PLOS Med
A large French study following nearly 103,000 adults for nearly 8 years found that people who consumed higher amounts of artificial sweeteners—particularly aspartame and acesulfame-K found in diet sodas and many processed foods—had a 13-15% increased risk of cancer overall, with specific increases in breast cancer and obesity-related cancers. The research, which carefully tracked detailed dietary records and controlled for multiple lifestyle factors, showed aspartame was associated with a 22% higher breast cancer risk among higher consumers compared to non-consumers. While the study has some limitations including potential confounding factors, these findings add to growing concerns about artificial sweetener safety and support the need for regulatory agencies to re-evaluate the safety of these widely used food additives found in thousands of products worldwide.
2022
BMC Med
A large UK study of 472,377 people followed for over 11 years found that vegetarians had 14% lower overall cancer risk compared to regular meat-eaters, with similar reductions seen in low meat-eaters (2% lower) and fish-eaters (10% lower). Vegetarian postmenopausal women had 18% lower breast cancer risk, though this benefit appeared to be largely explained by vegetarians having lower body weight, while men who ate fish or followed vegetarian diets had 20-31% lower prostate cancer risk. Low meat consumption was associated with 9% lower colorectal cancer risk, particularly in men, supporting previous evidence that meat intake increases cancer risk, though the study couldn’t definitively determine whether the observed benefits reflect direct dietary effects or other lifestyle factors associated with these eating patterns.
2007
Cancer
A comprehensive review found that while laboratory studies have identified numerous environmental chemicals that cause breast tumors in animals or mimic estrogen, human epidemiological evidence is strongest for PAHs (found in air pollution and grilled foods) and PCBs (banned industrial chemicals), particularly in women with certain genetic variations affecting how their bodies process these chemicals and hormones. Evidence linking dioxins and organic solvents to breast cancer is limited but suggestive, while many chemicals identified as mammary carcinogens in animal studies have never been investigated in human populations due to challenges in measuring past exposures and the decades-long delay between exposure and cancer diagnosis. The review argues that given these methodological limitations in human studies, policymakers should rely more heavily on animal and laboratory evidence to develop regulations that reduce chemical exposures, as waiting for definitive human proof may unnecessarily delay prevention strategies that could reduce breast cancer rates.