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2022
Environ Sci Pollut Res
The following study explores the presence of endocrine disruptors such as phthalates (specifically mono-2-ethyl phthalate and mono-n-butyl phthalate), bisphenol A (BPA), and 1-hydroxypyrene in the urine samples of marginalized Indigenous populations. The study found that 100% of the women sampled showed exposure to these harmful chemicals, with higher concentrations than observed in similar studies from other communities. This increased exposure is linked to environmental and cultural factors, such as the common use of plastic containers and practices such as burning garbage. The women sampled were found to have especially high levels of mono-2-ethyl phthalate, which suggests significant exposure to di(2-ethylhexyl) phthalate. These findings highlight the vulnerability of indigenous communities to pollution due to a lack of awareness, limited healthcare access, and inadequate regulatory measures.
2022
Molec Carcinogen
A case-control study of 708 breast cancer patients and 598 controls from Long Island found that paraben exposure—particularly methylparaben—was associated with significantly increased breast cancer risk among women with hypomethylated (undermethylated) DNA, showing a 46% increased risk in the highest versus lowest exposure group and a 32% increased risk per one-quantile increase in combined paraben exposure. Importantly, paraben exposure was specifically associated with breast tumors characterized by hypomethylation of the CCND2 gene promoter, with methylparaben showing a 25% increased risk and combined parabens showing a 55% increased risk for this tumor subtype. These findings suggest that parabens—ubiquitous preservatives in personal care products—may contribute to breast cancer development through epigenetic mechanisms, particularly in women with pre-existing DNA methylation abnormalities, identifying a potentially vulnerable subpopulation and a specific molecular pathway through which these chemicals may promote carcinogenesis.
2022
BMP Nutr Prev Health
A recent study found that ultra-processed food intake is associated with an increased risk of breast cancer in young women across Latin American countries. The study, involving 525 cases and 525 controls, revealed that major contributors to ultra-processed food intake included ready-to-eat meals, sugary beverages, processed meats, and packaged snacks. Ultra-processed foods are rich in unhealthy fats, sugars, and additives that may drive cancer risk. This highlights the need to reduce ultra-processed food consumption and promote healthier, whole-food diets as a preventative measure, especially among young women in Latin America.
2022
Endocrinology
A review examining PFAS (found in nonstick cookware, food packaging, and stain-resistant fabrics) and parabens (used in personal care products) found that exposure to these endocrine-disrupting chemicals is linked to breast cancer development, with marginalized and socially disadvantaged communities facing disproportionately higher exposures due to structural racism and inequitable environmental conditions. These disparities in chemical exposure may contribute to poorer breast cancer outcomes in these populations, yet breast cancer research continues to underrepresent these communities, limiting our ability to address treatment disparities and improve survival rates. The authors emphasize the urgent need to both reduce EDC exposures in vulnerable communities and increase research inclusion of diverse populations to understand how environmental injustices intersect with breast cancer risk and develop interventions that address these health inequities.
2022
Clin Breast Cancer
A case-control study of 150 Iranian women with newly diagnosed breast cancer matched with 150 controls found that women consuming the most pro-inflammatory diets (highest quartile of food-based dietary inflammatory index) had a 138% increased breast cancer risk compared to those with the least inflammatory diets, with the association remaining significant (180% increased risk) after adjusting for confounding factors. The food-based empirical dietary inflammatory index (FDII), which scores dietary patterns based on 27 pre-defined food groups according to their inflammatory potential, showed a clear dose-response relationship with breast cancer risk across quartiles. These findings from a Middle Eastern population reinforce that dietary patterns promoting systemic inflammation substantially increase breast cancer risk, and suggest that practical, food-based dietary modifications—emphasizing anti-inflammatory whole foods like fruits, vegetables, whole grains, legumes, nuts, and fish while limiting pro-inflammatory processed foods, red meat, and refined carbohydrates—could be an effective and culturally adaptable breast cancer prevention strategy.
2022
Int Arch Occup Environ Health
A nationwide retrospective cohort study of over 4.7 million Taiwanese workers found that occupational exposure to specific hazardous chemicals was associated with significantly elevated breast cancer risk among female workers, with asbestos showing the highest increase (107% increased incidence, 80% increased risk after adjusting for age and exposure duration). Other notable associations included 1,1,2,2-tetrachloroethane (74% increased incidence, 52% adjusted risk increase), trichloroethylene/tetrachloroethylene (47% increased incidence, 42% adjusted risk increase), benzene (40% increased incidence, 38% adjusted risk increase), and lead (27% increased incidence, 31% adjusted risk increase), with associations remaining robust even after accounting for 2- or 5-year latency periods. These findings from 3,248 breast cancer cases among exposed workers provide compelling evidence that occupational chemical exposures substantially increase breast cancer risk, highlighting the urgent need for enhanced workplace protections, regular breast cancer screening programs for exposed workers, substitution of safer alternatives where possible, and recognition of breast cancer as an occupational disease for workers with documented exposure to these carcinogens.
2022
Int J Epidemiol
A large European prospective study of 150,257 women followed for 14 years found that weight gain of more than 10 kg from age 20 to middle adulthood was associated with a 42% increased postmenopausal breast cancer risk among women who were lean at age 20, with the association present in both HRT users (23% increased risk) and non-users (40% increased risk) and particularly strong for ER+/PR+ breast cancers (46% increased risk). The findings indicate that maintaining stable weight from young adulthood is especially important for women who start out lean, as weight gain appears to negate the protective effect of lower early-life body weight. These results highlight a critical window for breast cancer prevention: while being lean in early adulthood is protective, this benefit is substantially diminished by subsequent weight gain, suggesting that weight management efforts should focus not just on current weight but on preventing long-term weight accumulation from young adulthood through menopause.
2022
Asian Pac J Cancer Prev
A matched case-control study of 187 breast cancer patients and 187 controls in Asia found that irregular sleep patterns and severe stress were the strongest modifiable risk factors, with irregular sleep associated with a staggering 3,311% increased breast cancer risk and severe stress showing a 574% increased risk. Poor sleep quality showed an even more dramatic 1,029% increased risk, while regular multivitamin use was associated with a 238% increased risk—a surprising finding requiring further investigation—and having a first child before age 30 was protective with a 56% risk reduction. Notably, none of the traditional non-modifiable risk factors (such as family history) showed significant associations in this study, suggesting that modifiable lifestyle factors—particularly sleep quality and stress management—may be critically important targets for breast cancer prevention in Asian populations experiencing rapidly rising breast cancer rates.
Risk of breast cancer in Danish women occupationally exposed to organic solvents, including ethanol.
2022
Am J Indust Med
A Danish nested case-control study of 845 breast cancer patients and 1,500 matched controls found that occupational exposure to organic solvents was associated with a 220% increased breast cancer risk among ever-exposed women compared to never-exposed women. The elevated risk was observed across all breast cancer subtypes—both estrogen receptor-positive and negative tumors—and in both pre- and postmenopausal women, though surprisingly, no dose-response relationship was detected with duration or cumulative exposure levels. Occupational ethanol exposure showed no association with breast cancer, suggesting that specific properties of other organic solvents may drive the carcinogenic effect, and highlighting the need for workplace protections and further research to identify which solvent types pose the greatest risk.
2022
Int J Cancer
A study of 881 Ghanaian women found that lower diversity of bacteria in the mouth was associated with increased risk of both breast cancer and nonmalignant breast disease, with specific bacterial types like Porphyromonas and Fusobacterium being less common in breast cancer patients. The research also revealed that among women with breast cancer, the composition of oral bacteria was strongly linked to their gut bacteria composition, while this connection was weak in healthy women. These findings suggest that the oral microbiome—the community of bacteria living in the mouth—may play a role in breast cancer risk and could potentially serve as a marker for disease, though more research is needed to understand how these bacteria might influence cancer development.
2022
Cancer Epidemiol Biomark Prev
A study of 102,572 women aged 40-69 years with normal BMI (18.5-<25 kg/m²) from the UK Biobank examined whether a healthy lifestyle index (HLI)—a composite score based on diet quality, low alcohol consumption, no smoking, moderate-to-high physical activity, and waist circumference <80 cm—was associated with breast cancer risk. Postmenopausal women with the highest HLI scores (3rd tertile) had a 24% reduced risk of breast cancer compared to those with the lowest scores (HR = 0.76; 95% CI: 0.64-0.91), while premenopausal women showed similar but non-significant trends, except when smoking was excluded from the score (HR = 0.71; 95% CI: 0.56-0.90). These findings demonstrate that even among women with normal BMI—a group traditionally considered at lower risk—adhering to multiple healthy lifestyle behaviors is associated with reduced breast cancer risk in postmenopausal women. The results suggest that maintaining a healthy lifestyle through diet, physical activity, limited alcohol, healthy waist circumference, and not smoking may provide breast cancer protection beyond weight management alone, particularly for postmenopausal women.
2022
Int J Obesity
A large retrospective cohort study using South Korea’s National Health Insurance Service database followed 691,253 premenopausal and 1,519,211 postmenopausal women aged ≥40 who underwent three consecutive biennial breast cancer screenings between 2009-2014 and were followed until 2020, identifying 9,485 and 12,553 breast cancer cases respectively over a median 6.9 years. In postmenopausal women, consecutive weight gains increased breast cancer risk by 11% while consecutive weight losses decreased risk by 16%; similarly, continuous increases in waist circumference raised risk by 13% while continuous decreases lowered risk by 16%, demonstrating a dose-response relationship. In premenopausal women, a single weight gain was associated with 7% increased breast cancer risk. These findings indicate that longitudinal changes in weight and waist circumference—not just baseline measurements—are important predictors of breast cancer risk in a dose-response manner, with the direction and consistency of changes over time being particularly significant for postmenopausal women, suggesting that sustained weight loss and waist reduction may be effective breast cancer prevention strategies even in midlife and beyond.
2022
Biomed Pharmacother
A review of endocrine-disrupting chemicals (EDCs)—ubiquitous substances found in cosmetics, plastic food packaging, and medicines that enter the body through skin, digestive, or respiratory routes—examined their toxic effects even at microgram doses on the female reproductive system and genetic mechanisms. EDCs disrupt endocrine functions by binding to steroid hormone receptors, interfering with hormone synthesis and secretion, and modulating epigenetic processes that can lead to gene expression disturbances, contributing to neoplastic diseases, neurological disorders, circulatory problems, and reproductive dysfunction. Prenatal exposure can affect offspring development, with particular impacts on ovarian function leading to reduced fertility through disturbances in steroid receptor function, steroidogenesis, and gametogenesis. The review emphasizes that despite widespread exposure to these chemicals in everyday products, continued research is needed to fully understand their effects on the female reproductive system and potential transgenerational impacts mediated through epigenetic mechanisms.
2022
Biomedicines
This study investigates the effects of di-(2-ethylhexyl) phthalate (DEHP), a common plasticizer, on female rats. It found that exposure to DEHP, even at realistic environmental doses, led to significant disruptions in the rats’ reproductive and thyroid systems. More specifically it found that even low exposure to DEHP over a period of 21 days resulted in a significant decrease in the levels of estrogen and progesterone, which correlated with damage to ovarian follicles. Additionally, the thyroid showed signs of damage, including alterations in hormone regulation. The data in this study suggests that DEHP can potentially lead reproductive issues and impaired ovarian and thyroid gland function.
2021
Oncol Rep
A review of organophosphorus pesticides (OPs)—among the most commonly used insecticides—and their association with hormone-mediated cancer found that OPs combined with estrogen induce transformation events in human breast epithelial cells, with in vitro studies showing these substances cause genomic instability through inactivation of tumor-suppressor genes and activation of oncogenes. Studies using immortalized non-tumorigenic human breast epithelial cell lines (MCF-10F) demonstrated that OPs like malathion and parathion, particularly in the presence of estrogen, affect cell cycle regulation, epidermal growth factor signaling pathways, drug metabolism, and genomic stability, leading to cellular transformation and signs of carcinogenesis. The findings suggest hormone-mediated carcinogenic effects of these widely used insecticides on breast cancer risk in women, with experimental models revealing the multistep process by which normal breast cells transform into malignant ones through combined exposure to environmental pesticides and estrogen, providing mechanistic insights into how occupational and environmental OP exposure may contribute to breast cancer development.
2021
Adv Pharmacol
A comprehensive review examining endocrine-disrupting chemicals (EDCs) in breast tissue concludes that hundreds of these environmental chemicals are entering human breast tissue and contributing to the global rise in breast cancer incidence through multiple biological mechanisms. Laboratory studies demonstrate that EDCs can activate all the established “hallmarks of cancer” in human breast cancer cells—even at concentrations measured in actual human breast tissue—with effects amplified when chemicals are present as mixtures rather than individually. The authors argue that EDCs must now be formally recognized as a breast cancer risk factor to enable prevention strategies that include reducing environmental chemical exposures, particularly given that the varied mixtures of EDCs found in individual breast tissues act through overlapping mechanisms to promote cancer development.
2021
Endocrinology
A comprehensive review of bisphenol A (BPA) research spanning over 20 years—from the landmark 1997 study showing reproductive effects in male mouse offspring at 2 µg/kg/day through the CLARITY-BPA study designed to bridge regulatory and scientific disagreements—found that thousands of animal studies and over 100 epidemiological studies report adverse effects at low doses, with CLARITY-BPA showing effects at 2.5 µg/kg/day, leading independent experts to recommend dropping the lowest observed adverse effect level 20,000-fold from 50,000 to 2.5 µg/kg/day. Despite this overwhelming evidence, the FDA continues to assert BPA is safe by rejecting low-dose data as “not biologically plausible” based on four incorrect assumptions criticized by the Endocrine Society as violating basic principles of endocrinology: that dose responses must be monotonic, thresholds exist below which there are no effects, both sexes must respond similarly, and only traditional toxicological guideline studies are valid. The review highlights a fundamental divide between regulatory approaches and endocrine science, demonstrating that traditional toxicology methods are insufficient for evaluating endocrine-disrupting chemicals like BPA, which can cause non-monotonic dose responses, sex-specific effects, and low-dose effects that challenge conventional assumptions about chemical safety, yet regulatory agencies continue to ignore modern endocrinology principles in favor of outdated toxicological paradigms.
2021
BMC Women's Health
A meta-analysis of 26 studies including over 1.3 million participants found that short-term night-shift work (<10 years) was associated with a 13% increased breast cancer risk, but surprisingly, long-term night-shift work (≥10 years) showed no statistically significant increased risk (8% increase, not significant). Flight attendants with long overnight flights showed elevated breast cancer risk, though unmeasured confounders may have influenced these results, and the increased risk in short-term workers was most robust in case-control studies that adjusted for reproductive factors and family history. The paradoxical finding that short-term but not long-term night-shift work showed significant associations contradicts the expected dose-response relationship and may reflect healthy worker bias (where women susceptible to night-shift effects leave such work before reaching 10 years), methodological limitations in measuring long-term exposures, or unmeasured confounding factors that accumulate differently over time.
2021
Int J Health Geogr
A systematic review and dose-response meta-analysis of 17 studies found that exposure to light at night (LAN)—both outdoor and indoor—was associated with an 11% increased breast cancer risk overall, with slightly stronger associations in premenopausal women (16% increased risk) and ER-positive breast cancers (9% increased risk). The dose-response analysis of outdoor LAN showed a linear relationship up to 40 nW/cm²/sr, after which the curve flattened, particularly among premenopausal women, suggesting a threshold effect. These findings provide the first comprehensive dose-response assessment of the LAN-breast cancer relationship and support growing concerns about light pollution as an environmental breast cancer risk factor, with implications for urban planning, building design, and personal light exposure habits—particularly for younger women who appear most vulnerable to the carcinogenic effects of circadian disruption from artificial light exposure at night.
2021
Aging
A meta-analysis of 14 studies including 312,885 women found that those consuming the most pro-inflammatory diets had a 37% increased breast cancer risk compared to women with the most anti-inflammatory diets. The association was significant in both premenopausal women (87% increased risk) and postmenopausal women (23% increased risk), with notably stronger effects observed in younger women. These findings suggest that dietary patterns promoting chronic inflammation are an independent risk factor for breast cancer across all ages, and that dietary interventions focused on anti-inflammatory foods—such as fruits, vegetables, whole grains, and omega-3 fatty acids—could be an important prevention strategy, particularly for premenopausal women who showed the strongest association.
2021
Sci Rep
A combined analysis of five Finnish cohorts including 6,374 postmenopausal women examined whether adherence to three dietary quality indices—the modified Nordic Diet (mNDI), modified Mediterranean diet (mMEDI), and modified Alternative Healthy Eating Index (mAHEI)—was associated with breast cancer risk over an average 10-year follow-up during which 274 breast cancer cases were diagnosed. The study found a borderline protective association for the highest versus lowest adherence to the Nordic Diet (HR = 0.67; 95% CI 0.48-1.01), but no significant associations for the Mediterranean diet (HR = 0.88) or Alternative Healthy Eating Index (HR = 0.89). The authors note that the Nordic Diet, which is more aligned with local Finnish food culture, showed the strongest protective trend, though the association did not reach statistical significance. These findings suggest that while healthy dietary patterns have been linked to prevention of various chronic diseases, their relationship with postmenopausal breast cancer risk is not clearly established, with limited evidence for dietary factors beyond alcohol consumption affecting breast cancer risk.
2021
Sci Rep
A nested case-control study of 4,401 breast cancer cases and 4,401 matched controls from the French E3N cohort found no overall association between long-term airborne cadmium exposure and breast cancer stage or tumor grade, but identified a striking 240% increased risk of invasive tubular carcinoma (ITC)—a specific breast cancer subtype—among women in the highest versus lowest quintile of cadmium exposure. The dose-response analysis suggested a linear relationship between cadmium exposure and ITC risk specifically, though no associations were found for other histological subtypes or more advanced disease. These findings suggest that cadmium’s estrogenic properties may selectively promote certain breast cancer subtypes rather than broadly increasing all breast cancer risk, highlighting the importance of examining cancer heterogeneity in environmental exposure studies and raising concerns about air pollution from industrial sources, waste incineration, and fossil fuel combustion that release cadmium into the environment.
2021
Cancer Epidemiol Biomark Prev
A prospective study of 169,985 women from the Nurses’ Health Study cohorts followed over nearly 5 million person-years identified 12,482 invasive breast cancer cases and found that greater adherence to overall plant-based diets (PDI) and healthful plant-based diets (hPDI) was associated with 11% lower breast cancer risk (HR = 0.89 for both). The protective effect was strongest for ER-negative tumors, with women in the highest quintile of hPDI having 23% lower risk (HR = 0.77; 95% CI: 0.65-0.90) and those consuming the most healthy plant foods having 26% lower risk (HR = 0.74) of ER-negative breast cancer. This first prospective study examining healthful versus unhealthful plant-based dietary patterns suggests that high-quality plant-based diets may particularly protect against aggressive, hormone receptor-negative breast cancers.
2021
Breast
A systematic review of 22 studies found that breast skin harbors distinct bacterial communities, with imbalances in these bacteria—particularly certain Staphylococcus species—linked to breast cancer, metastases, inflammation, and implant complications. The research suggests bacteria can migrate from skin into underlying breast tissue through milk ducts, damaged skin barriers, or nipple fluid, potentially contributing to disease development. These findings indicate that breast skin bacteria may be a modifiable risk factor for breast diseases, opening possibilities for using probiotics, antimicrobials, or microbiome-based diagnostics as new tools for prevention, diagnosis, and treatment of breast conditions.
2021
Environ Res
Biodegradable polymers are emerging as a promising solution for removing endocrine-disrupting chemicals (EDCs) from wastewater. EDC’s, found in pharmaceuticals, pesticides, and personal care products pose serious health risks, impacting the endocrine system and disrupting reproductive health. Traditional water treatments often fail to fully remove EDCs. Biodegradable polymers, with strong adsorptive properties, offer a sustainable and effective method, helping to minimize EDC exposure and protect human and environmental health.
2021
Int J Environ Res Pubilc Health
A case-control study of 494 breast cancer cases and 515 healthy controls in Poland’s Lodz region (2015-2019) found that night shift work was the third most important breast cancer risk factor after high BMI and short/no breastfeeding, ranking before early menstruation, late menopause, nulliparity, and smoking. Night work increased breast cancer risk 2.34-fold, with high-intensity night work showing an even greater 2.66-fold increase, and the harmful effects were influenced by intensity, frequency, rotation patterns, and cumulative years of night shift exposure. The findings support the IARC’s 2019 classification of night shift work as probably carcinogenic (Group 2A) and emphasize the need for ergonomic recommendations to minimize breast cancer risk among night shift workers through optimized scheduling practices.
2021
Eur J Epidemiol
A large prospective study of 318,686 European women followed for 14 years found that consuming a pro-inflammatory diet was associated with a 4% increased breast cancer risk per standard deviation increase in inflammatory diet score, with women in the most pro-inflammatory diet group showing a 12% increased risk compared to those consuming the least inflammatory diets. The association was particularly strong in premenopausal women (8% increased risk per standard deviation), and notably, the pro-inflammatory diet effect was independent of body mass index, physical activity, and alcohol consumption, suggesting that dietary inflammation contributes to breast cancer risk through pathways distinct from these other established risk factors. The consistent associations across all hormone receptor-defined breast cancer subtypes suggest that dietary inflammation may promote breast cancer through non-hormonal mechanisms, reinforcing the importance of anti-inflammatory dietary patterns—rich in fruits, vegetables, whole grains, and omega-3 fatty acids while limiting processed foods, red meat, and refined carbohydrates—as a modifiable strategy for breast cancer prevention across all women, particularly those still premenopausal.
2021
Nutr Cancer
A case-control study of 317 breast cancer patients and 526 controls in Córdoba, Argentina found that women consuming the most pro-inflammatory diets (highest Dietary Inflammatory Index scores) had a 34% increased breast cancer risk compared to those with the least inflammatory diets. The association was markedly stronger among overweight and obese women, who showed a 98% increased risk with pro-inflammatory diets, and the effect was amplified in more urbanized areas compared to rural settings. These findings suggest that dietary patterns promoting systemic inflammation contribute to breast cancer risk, particularly in combination with obesity and urban lifestyle factors, highlighting the potential for dietary interventions focused on anti-inflammatory foods as a prevention strategy, especially in overweight women living in urban environments.
2021
PLOS One
A case-control study in Ethiopia examined 50 breast cancer patients and 50 controls to investigate whether exposure to organochlorine pesticides is a risk factor for breast cancer in a low- and middle-income country context. Ten organochlorine pesticides were detected in participants’ serum, with heptachlor found at highest concentrations; mean serum levels of p,p’-DDE, p,p’-DDT, heptachlor, gamma-chlordane, endosulfan, and dibutyl-chlorendate were significantly higher in breast cancer patients than controls, and p,p’-DDT and gamma-chlordane emerged as significant predictors of breast cancer, with each unit increase in p,p’-DDT concentration doubling breast cancer odds (AOR = 2.03; 95% CI: 1.04-3.97) and each unit increase in gamma-chlordane tripling the odds (AOR = 3.12; 95% CI: 1.19-8.20). These findings suggest that organochlorine pesticide exposure may be a significant breast cancer risk factor in Ethiopia, where environmental contamination from these persistent organic pollutants remains a concern despite global restrictions. The study highlights the public health importance of reducing exposure to these banned or restricted pesticides in developing countries and emphasizes the need for continuous biomonitoring of persistent organic pollutants to inform disease prevention strategies and mitigation measures, particularly as breast cancer incidence rises in low- and middle-income countries where environmental regulation may be less stringent.
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
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
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
Alcohol Alcohol
A meta-analysis of 22 cohort studies including 45,350 breast cancer cases found that each 10 grams per day increase in alcohol consumption (approximately one standard drink) was associated with a 10.5% increased breast cancer risk overall, with postmenopausal women showing an 11.1% increased risk per 10 grams daily. Wine showed a similar dose-response relationship (8.9% increased risk per 10g/day), while beer and spirits did not show significant linear associations in the dose-response analysis, and the risk was particularly elevated for estrogen receptor-positive (ER+) breast cancers. The alcohol-attributable percentage of breast cancer cases was highest in Europe compared to North America and Asia, suggesting that current drinking recommendations may need to explicitly address breast cancer risk, particularly for postmenopausal women and wine drinkers.
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
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
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
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
Breast Cancer Res Treat
A pilot study of 37 breast cancer patients found that women with HER2-positive breast cancer (an aggressive subtype) had 12-23% lower gut bacterial diversity and different bacterial compositions compared to HER2-negative patients, with less Firmicutes and more Bacteroidetes bacteria. The research also revealed that women who started menstruating early (age 11 or younger) and those with higher body fat had lower gut bacterial diversity, suggesting links between gut microbiome composition and known breast cancer risk factors. While the study was small, these findings indicate that gut bacteria composition may be connected to both breast cancer characteristics and established risk factors, warranting larger studies to better understand these relationships and their potential implications for prevention and treatment.
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
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.
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.