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Association between Urinary Lead and Female Breast Cancer: A Population-Based Cross-Sectional Study.
2023
Discov Med
This study analyzed data from nearly 2,800 women in the National Health and Nutrition Examination Survey (NHANES) to investigate whether urinary lead levels are associated with breast cancer risk. Researchers found that higher urinary lead levels were positively associated with breast cancer, with women having the highest lead levels showing 2.16 times the odds of breast cancer compared to those with the lowest levels, and this association persisted after adjusting for numerous factors including age, BMI, smoking, and socioeconomic status. The positive trend was consistent across different subgroups of women regardless of age, race, pregnancy history, or other health conditions. These findings suggest that lead exposure, as measured in urine, may be a risk factor for breast cancer in US women.
2022
BMC Med
A large European study measuring inflammatory markers in the blood of over 3,000 women found that inflammation’s relationship with breast cancer risk differs dramatically by menopausal status, with higher levels of leptin and C-reactive protein (CRP) appearing protective in premenopausal women but associated with increased risk in postmenopausal women. The opposing effects were particularly evident for leptin and CRP, which showed 11-17% lower breast cancer risk in premenopausal women but 10-16% higher risk in postmenopausal women, and these associations were influenced by body weight. These findings suggest that inflammation and obesity may affect breast cancer development through different biological mechanisms before and after menopause, highlighting the importance of considering menopausal status when assessing breast cancer risk factors.
2021
Environ Pollut
A pilot study of 250 predominantly postmenopausal women in Hawaii found that higher levels of AMPA (the primary breakdown product of the herbicide Glyphosate) in urine were associated with significantly increased breast cancer risk, with women in the highest exposure group having 4.5 times the risk compared to those with the lowest exposure. AMPA was detected in the urine of 90% of breast cancer cases and 84% of healthy controls, with cases showing 38% higher average AMPA levels. This is the first study to prospectively examine the link between AMPA exposure and breast cancer, and while the findings suggest a concerning association, the authors emphasize that larger studies are needed to confirm these preliminary results and explore potential differences across racial and ethnic groups.
2021
Int J Cancer
In a nested case-control study of over 1,000 breast cancer cases and matched controls from the Multiethnic Cohort, pre-diagnostic urinary concentrations of bisphenol A (BPA), triclosan, and parabens were evaluated in relation to breast cancer risk. BPA was not significantly associated with risk; the highest tertile of total parabens had OR ≈ 0.77 (95% CI: 0.62–0.97) relative to the lowest tertile, indicating a modest inverse association. These results suggest that the relationships between common endocrine-disrupting chemicals and breast cancer may be more complex than anticipated and vary by exposure type.
2020
Cancer Epidemiol
A study of 186,981 postmenopausal women in the NIH-AARP Diet and Health Study found that those living in areas with the highest levels of outdoor light at night (LAN) had a 10% increased risk of developing breast cancer over 16 years of follow-up compared to women in the darkest areas. The association was stronger for estrogen receptor-positive breast cancer (12% increased risk) and appeared to vary by individual characteristics such as smoking, alcohol consumption, sleep duration, and body mass index. These findings suggest that nighttime light pollution may disrupt circadian rhythms and contribute to breast cancer development, particularly hormone-sensitive tumors. The results highlight artificial light at night as a potentially modifiable environmental risk factor for postmenopausal breast cancer, with implications for urban planning and outdoor lighting policies.
2019
Environ Int
A population-based study of 711 breast cancer cases and 598 controls from the Long Island Breast Cancer Study Project measured seven urinary phenol biomarkers (environmental endocrine disruptors from personal care and consumer products) in spot urine samples collected within three months of diagnosis, with 17.6-year median follow-up identifying 271 deaths including 98 from breast cancer. The highest versus lowest quintiles of methylparaben, propylparaben, and sum of parabens (Σparabens) were associated with 31-50% increased breast cancer risk (ORs: 1.31-1.50) but paradoxically with 23-32% reduced all-cause mortality after diagnosis (HRs: 0.68-0.77), with associations for incidence stronger among women with BMI <25 kg/m² and associations for mortality stronger among women with BMI ≥25 kg/m². These findings—the first to examine phenol biomarkers in relation to both breast cancer incidence and subsequent mortality—reveal complex differential associations suggesting that select parabens may increase risk of developing breast cancer but be associated with better survival outcomes, though the mechanisms underlying these paradoxical associations remain unclear and may relate to BMI-dependent metabolic or hormonal factors, reverse causation, or unmeasured confounding.
2018
Environ Health
This longitudinal study examined how exposure to endocrine disrupting chemicals (EDCs) affects the timing of menarche in Chilean girls by measuring 26 phenol and phthalate compounds in urine samples collected before breast development and during adolescence. The researchers found that different chemicals had varying effects depending on when exposure was measured: higher early exposure to DEHP was associated with later menarche, while early exposure to certain phenols and later exposure to some phthalates were linked to earlier menarche. The study also revealed that body weight influenced these effects, with overweight or obese girls showing earlier menarche when exposed to higher levels of certain chemicals like triclosan, while normal-weight girls did not show this association. These findings demonstrate that specific EDCs can disrupt normal sexual development in girls, with timing of exposure and body weight being important factors.
2025
Global Health Res Pol
A meta-analysis of 17 observational studies found that the highest consumption of fast foods and ultra-processed foods (FFs/UPFs) was associated with a 25% increased breast cancer risk compared to the lowest consumption levels. The association was particularly strong in case-control studies and in Latin American populations, and remained significant regardless of sample size or BMI adjustment, though no association was found in cohort studies or when stratified by menopausal status. These findings suggest that diets high in ultra-processed foods—which often contain carcinogenic compounds formed during processing, additives, packaging contaminants, and unhealthy nutrient profiles—may contribute to breast cancer development, highlighting the urgent need for public health strategies and regulatory policies targeting food processing standards, marketing restrictions, improved labeling, and reduced accessibility of ultra-processed foods to reduce cancer risk, particularly as global consumption of these products continues to rise.
2025
Sci Rep
A secondary analysis of 15,536 post-menopausal women from the Alberta Tomorrow Project cohort examined whether exposure to traffic-related air pollution (TRAP), measured using nitrogen dioxide (NO₂) levels, was associated with breast cancer risk over 12.6 years of follow-up during which 523 breast cancer cases were diagnosed. After adjusting for confounders including age, education, births, diet, income, physical activity, BMI, and smoking, the study found no significant association between NO₂ exposure and post-menopausal breast cancer risk (HR = 1.10 per 10-ppb increase in NO₂; 95% CI = 0.90, 1.34). The authors suggest that while the magnitude of risk observed was similar to other studies, the lack of statistical significance may be due to the study’s sample size limitations and the fact that NO₂ levels in Alberta are lower than in many other regions globally where associations have been found. These findings indicate that traffic-related air pollution may not significantly impact post-menopausal breast cancer risk in regions with relatively low pollution levels, though larger studies in more polluted areas may be needed to fully assess this relationship.
2025
Breast Cancer
A meta-analysis of 10 studies involving 1,730 women found that breast cancer patients had significantly lower gut bacterial diversity compared to healthy controls, with particularly pronounced differences in premenopausal women and women with normal body weight. The reduction in gut microbiome diversity—a marker of gut health—was not seen in overweight or obese women, suggesting body weight may influence the relationship between gut bacteria and breast cancer. These findings support the hypothesis that gut bacteria may play a role in breast cancer development, possibly through their influence on estrogen levels, though more research is needed to understand the underlying mechanisms and whether improving gut health could help prevent breast cancer.
2025
Sci Rep
A large U.S. study of 4,455 people found that exposure to triclosan (TRS)—an antibacterial chemical commonly found in soaps, toothpaste, and personal care products—was associated with more than double the risk of breast cancer at moderate exposure levels, with the relationship following an inverted U-shape pattern. The association was strongest among overweight individuals, people under 60 years old, and white participants, while other tested chemicals (including bisphenol A, benzophenone-3, and parabens) showed no significant link to breast cancer risk. These findings suggest that triclosan exposure may be an important modifiable risk factor for breast cancer, particularly for certain population groups, though more research is needed to understand the underlying mechanisms and confirm causality.
2025
Nutr J
A prospective cohort study of 13,567 Chinese women followed for nearly 15 years found that consuming one or more servings of sugar-sweetened beverages (SSBs) per week was associated with a 58% increased breast cancer risk compared to consuming less than one serving weekly. The association was partly mediated by body mass index (4.2%) and uric acid (18.8%), with genetic analyses identifying additional metabolic mediators including cholesterol and fatty acid ratios accounting for small portions of the effect. Interestingly, higher soy milk consumption (3-6 portions weekly) was associated with a 69% reduced breast cancer risk, while dairy milk showed a non-significant trend toward increased risk, and no associations were found for juice, coffee, tea, or alcohol, suggesting that reducing SSB consumption and addressing the associated metabolic disruptions could be effective breast cancer prevention strategies.
2024
Cancer Epidemiol
A large collaborative study of 609,880 women from 16 prospective studies, including 9,956 breast cancer cases before age 55, examined when the relationship between body mass index (BMI) and breast cancer risk transitions from protective (before menopause) to harmful (after menopause). During the critical age window of 45-55 years, the study found that a five-unit BMI increment remained associated with reduced or neutral breast cancer risk across all menopausal status groups: HR=0.87 for premenopausal women, HR=1.00 for women after natural menopause, HR=0.99 after interventional loss of ovarian function, and HR=0.88 after hysterectomy without bilateral oophorectomy. The findings indicate that the well-documented reversal from BMI being protective to being a risk factor for breast cancer occurs after age 55, later than previously thought, suggesting that the transition to increased risk with higher BMI is not directly tied to the menopausal transition itself but occurs in the years following menopause. This timing provides important insight into how adiposity influences breast cancer risk across the lifespan and suggests that the hormonal and metabolic changes associated with higher BMI have different effects on breast tissue depending on age and years since menopause.
2024
Br J Cancer
A large prospective study of 1,275,783 women aged 45+ years followed for a median 12.7 years from 2004 examined associations between menopausal hormone therapy (HT) types and breast cancer risk, finding that oral estrogen combined with daily progestin carried the highest risk (HR=2.42; 95% CI: 2.31-2.54), with drug-specific hazard ratios ranging from Cliovelle® (HR=1.63) to Kliogest® (HR=2.67), while vaginal estradiol showed no association with breast cancer. The associations varied substantially by molecular subtype (stronger for luminal A: HR=1.97 vs. other subtypes), detection mode (stronger for interval-detected: HR=2.00 vs. screen-detected cancers: HR=1.33 in women 50-71), and BMI (decreasing hazard ratios with increasing BMI). These contemporary findings confirm that oral and transdermal HT use increases breast cancer risk with important variation by specific formulations, administration routes, tumor characteristics, and patient factors, providing critical updated evidence for clinical decision-making about menopausal hormone therapy use and emphasizing the need for individualized risk-benefit assessment accounting for HT type, body weight, and cancer screening participation.
2024
Breast Cancer Res Treat
A large prospective study of 187,278 nurses followed for up to 31 years found that high levels of recreational physical activity (≥27 vs <3 MET-hours/week, roughly equivalent to ≥9 hours/week of brisk walking) were associated with 17% reduced breast cancer risk in both premenopausal and postmenopausal women. The protective effect was strongest for hormone receptor-positive (ER+/PR+) tumors in both groups, with no significant associations observed for hormone receptor-negative cancers, and while the benefit in postmenopausal women was partly explained by lower body weight, the association in premenopausal women remained independent of BMI. These findings provide strong evidence that regular recreational physical activity is a modifiable risk factor that reduces breast cancer risk across the lifespan, regardless of menopausal status, supporting public health recommendations for regular exercise as an accessible breast cancer prevention strategy for all women.
2024
J Clin Oncol
The aim of this pooled analysis (taking data from 19 cohort studies from around the world) was to determine the effect (if any) of leisure-time physical activity on the premenopausal risk of breast cancer. Leisure time physical activity is defind as physical activity occuring during free time (so, not related to work). This analysis took data from a little over half a million women, where the incidence of breast cancer was about 10,000 across the studies. Hazard ratios (how often breast cancer occured in groups w/ high activity versus low activity) was used to asses relative risk. High levels of leisure time activity were associated with an approximately 10% reduction in breast cancer risk after adjusting for BMI. This association was found to be particuarily strong for human epidermal growth factor receptor 2–enriched breast cancer, with a 16-61% reduction in risk.
2024
Ann Med
A study of 1,789 participants (including 263 breast cancer patients) from the National Health and Nutrition Examination Survey (NHANES) examined the associations between sleep duration, depression, and breast cancer risk, and developed machine learning algorithms to predict breast cancer. The study found that participants with depression had nearly double the odds of breast cancer (OR = 1.99; 95% CI: 1.55-3.51), while no significant association was observed between sleep duration (<7 hours, >9 hours compared to 7-9 hours) and breast cancer risk. Among six machine learning algorithms tested, the AdaBoost model performed best in predicting breast cancer with an area under the curve (AUC) of 0.84 (95% CI: 0.81-0.87), demonstrating good predictive capability. These findings suggest that depression, but not sleep duration, is significantly associated with increased breast cancer risk, providing new insights into the relationship between mental health and breast cancer while highlighting the need for further research into the underlying pathological mechanisms connecting depression and breast cancer development.
2023
Nutrients
A case-control study of 42 newly diagnosed, treatment-naïve breast cancer patients and 44 age-matched cancer-free controls at Oregon Health & Science University (2020-2021) found reduced gut microbial diversity in breast cancer patients and enrichment of three specific bacterial genera—Acidaminococcus, Tyzzerella, and Hungatella—in fecal samples from cases, with these genera associated with distinct dietary patterns including vegetables and dairy (Hungatella) and whole fruits (Acidaminococcus). Breast cancer patients also had significantly higher BMI and lower physical activity levels, and microbiome analysis revealed significant differences in composition between cases and controls using 16S rRNA sequencing. These findings highlight complex interactions between the gut microbiome, dietary habits (assessed via National Cancer Institute Diet History Questionnaire), lifestyle factors like weight management and physical activity, and breast cancer risk, suggesting the gut microbiome may serve as a source of biomarkers for breast cancer risk assessment, though larger studies are needed to establish causal relationships and validate these microbial signatures.
Low Vitamin D level increases women’s breast cancer risks, Sulaimaniyah, Iraq: A case-control study.
2023
Cell Mol Biol
A case-control study of 130 women (65 breast cancer patients, 65 healthy controls) aged 20-60 at Shar Hospital in Sulaimaniyah, Iraq found that 66.1% of breast cancer patients had vitamin D deficiency (<20 ng/L) compared to 43.1% of controls, with significantly lower mean vitamin D levels in cases (17.8±8.6) versus controls (20.2±8.7), and vitamin D levels below 20 ng/L associated with 2.59-fold increased breast cancer risk (OR=2.59; 95% CI: 1.24-5.38). After adjusting for age and BMI, vitamin D insufficiency remained a significant breast cancer risk factor (AOR=2.30; 95% CI: 1.1-4.86 for patients; AOR=3.67; 95% CI: 1.55-8.7 for controls). These findings indicate that vitamin D insufficiency substantially increases breast cancer risk among Iraqi women, supporting the role of vitamin D in breast cancer prevention and highlighting the importance of maintaining adequate vitamin D levels, particularly in populations with high deficiency rates.
2023
Ann Agric Environ Med
A case-control study of 111 postmenopausal women with breast cancer and 111 controls found that shift work was associated with a 165% increased breast cancer risk, but this risk was dramatically amplified by body weight status. Overweight shift workers showed a staggering 884% increased breast cancer risk compared to normal-weight women who had never worked shifts, indicating a powerful synergistic effect between shift work and excess body weight. With 72% of breast cancer cases having a history of shift work compared to 49% of controls, these findings suggest that the combination of circadian disruption from shift work and metabolic dysfunction from excess weight creates a particularly high-risk scenario, highlighting the urgent need for targeted prevention strategies—including weight management and lifestyle interventions—specifically for women working non-standard hours.
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
Nutr Cancer
An updated meta-analysis of 21 studies including over 346,000 participants found that the most pro-inflammatory diets were associated with a 16% increased breast cancer risk overall, with particularly strong associations among postmenopausal women (13% increased risk), obese women with BMI ≥30 kg/m² (35% increased risk), and populations in developing countries (79% increased risk). The analysis revealed important methodological influences on effect estimates, with stronger associations observed in case-control studies (50% increased risk), studies using hospital-based controls (111% increased risk), and cohort studies with prolonged follow-up (13% increased risk). These findings not only confirm that pro-inflammatory dietary patterns increase breast cancer risk but also demonstrate that the magnitude of association varies substantially by population characteristics and study design, with obesity and postmenopausal status appearing to amplify the carcinogenic effects of inflammatory diets—suggesting that anti-inflammatory dietary interventions may be particularly beneficial for overweight/obese postmenopausal women and populations in developing countries where rapid dietary transitions toward processed, inflammatory foods are occurring.
2022
Cancer Epidemiol
A case-control study of 508 breast cancer cases and 892 controls from the Nigerian Integrative Epidemiology of Breast Cancer (NIBBLE) Study examined associations between leisure-time physical activity (LTPA) and breast cancer risk by molecular subtype, with immunohistochemical analysis available for 294 cases (43.2% hormone receptor-positive [HRP], 41.8% triple-negative [TNBC]). Women in the highest LTPA quartile (≥14.75 METs/hour/week) compared to the lowest (<3.75) had 49% lower odds of breast cancer overall (OR=0.51; 95% CI: 0.35-0.74) and 49% lower odds of TNBC (OR=0.51; 95% CI: 0.27-0.96) after adjusting for age, reproductive factors, body size, and other confounders, though the association with HRP breast cancer was not statistically significant (OR=0.61; 95% CI: 0.34-1.09), with stronger protective effects observed in women with BMI<30 versus BMI≥30. These findings suggest that leisure-time physical activity may reduce breast cancer risk in Sub-Saharan African women, particularly for triple-negative breast cancer—the more aggressive and prevalent molecular subtype in this population—highlighting physical activity as a potentially important modifiable risk factor for breast cancer prevention in African populations where TNBC rates are disproportionately high.
2022
Int J Cancer
A comprehensive two-sample Mendelian randomization study using Breast Cancer Association Consortium data examined potential causal associations of 23 risk factors and biomarkers with breast cancer risk overall and by molecular subtypes, identifying significant associations for 15 traits including reproductive factors (age at menarche/menopause), anthropometric measures (BMI, waist-to-hip ratio, height), lifestyle factors (physical activity, smoking, sleep duration, chronotype), and six blood biomarkers (estrogens, IGF-1, SHBG, telomere length, HDL-cholesterol, fasting insulin). Notably, the study revealed heterogeneous subtype-specific associations: increased SHBG reduced ER+ breast cancer risk (OR=0.83; 95% CI: 0.73-0.94) but elevated risk for ER- (OR=1.12) and triple-negative cancers (OR=1.19, p-heterogeneity=0.01), while higher fasting insulin increased HER2-negative cancer risk (OR=1.94; 95% CI: 1.18-3.20) but reduced HER2-enriched cancer risk (OR=0.46; 95% CI: 0.26-0.81, p-heterogeneity=0.006). These findings—consistent across sensitivity analyses—provide strong genetic evidence for causal relationships between multiple modifiable and biological risk factors and breast cancer, while revealing that SHBG and insulin have paradoxical opposite effects on different molecular subtypes, suggesting distinct etiologic pathways for ER+/ER- and HER2+/HER2- breast cancers that may require subtype-specific prevention strategies.
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
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.
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.
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
Environ Health
A nested case-control study of 197 incident postmenopausal breast cancer cases and 197 controls with blood samples collected 1994-1999 measured plasma levels of six PBDE congeners (BDE-28, -47, -99, -100, -153, -154) and PBB-153 using gas chromatography-mass spectrometry and found no overall evidence of association between brominated flame retardant (BFR) levels and breast cancer risk (log-concentrations yielding odds ratios of 0.87-1.07). Some analyses showed non-linear inverse associations for BDE-100 and BDE-153 with breast cancer risk (third vs. first quintile: OR=0.42; 95% CI: 0.19-0.93 and OR=0.42; 95% CI: 0.18-0.98, respectively) when exposure was modeled as ng/L plasma but not when lipid-adjusted (OR=0.58 and 0.53), with results unchanged by tumor hormone receptor status or BMI. These findings suggest no clear association between internal PBDE and PBB-153 levels and postmenopausal breast cancer risk, though limitations include small sample size, lack of genetic susceptibility information, single time-point exposure assessment that may not represent critical windows of susceptibility, and the paradoxical inverse associations requiring cautious interpretation, warranting additional larger studies with repeated measurements and assessment of early-life exposures to clarify the relationship between BFR exposure and breast cancer development.
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
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
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
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.
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
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.
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
BMC Cancer
A prospective analysis of 657 incident breast cancer cases from the EPIC-Germany Study (n=27,012) with immunohistochemical characterization of tumors by six markers (ER, PR, HER2, Ki67, Bcl-2, p53) found that among postmenopausal women not using hormone therapy (HT), higher BMI was significantly associated with increased risk of less aggressive tumors characterized by ER+, PR+, HER2-, low Ki67, Bcl-2+, and p53- status (HR per 5 kg/m²: 1.44; 95% CI: 1.10-1.90) but not more aggressive subtypes, while among postmenopausal HT users, BMI showed a significant inverse association with less aggressive tumors (HR per 5 kg/m²: 0.68; 95% CI: 0.50-0.94). Among pre- and perimenopausal women, no significant linear associations emerged, though the highest BMI tertile showed significantly lower risk of less aggressive tumors (HR: 0.55; 95% CI: 0.33-0.93). These findings suggest that obesity’s relationship with breast cancer is highly nuanced, being associated with increased risk of less aggressive, hormone-responsive tumors in postmenopausal women not using HT, paradoxically protective in HT users and younger women, highlighting the complex interplay between adiposity, endogenous and exogenous hormones, menopausal status, and tumor biology that requires replication in larger pooled prospective studies.
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.
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
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
Curr Oncol Rep
Obesity is now recognized as a leading preventable cause of cancer, particularly postmenopausal estrogen receptor-positive breast cancer, and is associated with worse outcomes across all breast cancer subtypes. Multiple interconnected mechanisms link obesity to breast cancer, including elevated estrogen levels, altered hormone-like molecules from fat tissue (leptin and adiponectin), disrupted insulin signaling, changes in gut bacteria, and chronic inflammation throughout the body. Understanding these complex pathways could lead to new prevention and treatment strategies to reduce the growing burden of obesity-related breast cancers worldwide.
2017
Molec Cell Endocrinol
This study examines the role of environmental estrogen-like endocrine-disrupting chemicals (EEDs) in breast cancer development. EEDs are synthetic compounds that mimic estrogen, and the ones being studied in this paper include polychlorinated biphenyls (PCBs), bisphenol A (BPA), and phthalates. The results of the study show that of the EEDs tested, only one type of PCB, PCB138, had a strong association with the formation of breast cancer, where as phthalates (and it metabolites) but and BPA showed no strong correlation. Additionaly, the researchers identify that these EEDs promote the proliferation of breast cancer cells, induce epigenetic changes that may increase susceptibility to cancer, as well as alter developmental pathways during critical windows of breast development.
2024
Mol Nutr Food Res
A case-control study of 122 breast cancer patients and 56 healthy women in Southern Spain found that despite higher adherence to the Mediterranean diet, women with breast cancer had elevated body mass index (BMI), higher metabolic syndrome markers (glucose, cholesterol), and distinct gut microbiota alterations compared to controls. The most significant microbiota difference was a higher Bacillota/Bacteroidota ratio in breast cancer patients, a characteristic typically associated with metabolic dysfunction. The paradoxical finding—better diet quality alongside metabolic abnormalities—suggests that lifestyle changes around diagnosis or the influence of BMI may have masked the typical metabolic benefits of Mediterranean diet adherence, highlighting the complex interplay between diet, metabolism, gut microbiota, and breast cancer risk.
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.