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2023
Breast Cancer Res
This large study of over 181,000 women from the UK Biobank examined whether allostatic load (AL)—a measure of cumulative physiological stress on the body over time—is associated with breast cancer risk. Women with higher AL scores had a significantly increased risk of developing breast cancer, with each one-unit increase in AL associated with a 5% higher risk, and women in the high AL group showing a 17% increased risk compared to those in the low AL group, even after accounting for known risk factors like family history, lifestyle, and genetic factors. The association was found across multiple subgroups and appeared independent of traditional breast cancer risk factors, suggesting that chronic physiological stress may contribute to breast cancer development. These findings indicate that AL could serve as a valuable biomarker for predicting and stratifying breast cancer risk in women.
2022
Am J Prev Med
A systematic review of five studies examining physical activity during adolescence and young adulthood in women with BRCA1/BRCA2 gene mutations found that higher activity levels may reduce or delay breast cancer risk later in life. Four of the five studies showed protective effects, with one specifically finding a 38% reduction in premenopausal breast cancer risk and another showing that active young women developed breast cancer at older ages. However, the limited number of studies and reliance on self-reported activity data suggest that while the findings are promising, more research is needed to confirm whether early-life physical activity can help protect BRCA mutation carriers from breast cancer.
2025
Int J Environ Res Public Health
A prospective study of 10,305 women in Nova Scotia found that frequent sleep trouble (“all of the time”) was associated with a 141% increased breast cancer risk, while high physical activity was associated with a 42% reduced risk. Interestingly, sleep duration itself showed no association with breast cancer risk, suggesting that sleep quality—rather than quantity—may be the more important factor. These findings add sleep disturbances to the list of modifiable lifestyle risk factors for breast cancer and reinforce the protective benefits of physical activity, though the authors note that further research is needed to understand the biological mechanisms linking poor sleep quality to increased cancer risk.
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
Clin Transl Oncol
A review of 29 studies found that breast cancer patients have distinct imbalances in their gut and breast tissue bacteria that vary based on cancer type, stage, menopause status, body weight, and physical activity, though no single bacterial profile has yet emerged as a reliable biomarker. The research suggests that gut microbiome composition may influence how well breast cancer treatments work, with some beneficial bacteria and their metabolites potentially improving therapy effectiveness or slowing tumor growth. These findings highlight the microbiome as a promising new area for developing personalized breast cancer treatments and improving outcomes, though more research is needed to identify specific bacterial targets and understand the underlying mechanisms.
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
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.
2023
Breast Cancer Res Treat
A study of 1,398 Black women (567 breast cancer cases, 831 controls) found preliminary evidence of gene-environment interactions between genetic variants in the mTOR signaling pathway and vigorous physical activity affecting breast cancer risk, though results did not survive correction for multiple testing. Specific variants in AKT1 were associated with 49-85% reduced ER-positive breast cancer risk only among physically active women, while an MTOR variant showed a 124% increased ER-positive cancer risk and an EIF4E variant showed dramatically elevated ER-negative cancer risk (over 20-fold), but only in the context of vigorous physical activity. These exploratory findings suggest that the relationship between physical activity and breast cancer may vary by genetic background in Black women, potentially explaining some of the heterogeneity in physical activity-breast cancer associations, though larger studies with multiple testing correction are needed to confirm whether these gene-exercise interactions truly modify breast cancer risk.
2023
Cancer Epidemiol Biomark Prev
A systematic review and meta-analysis of 34 observational studies and 3 Mendelian randomization studies found that women with the highest levels of C-reactive protein (CRP)—a marker of systemic inflammation—had a 13% increased breast cancer risk compared to those with the lowest levels, though the quality of evidence was rated as very low to moderate. While adiponectin showed a protective association (24% reduced risk), this finding was not supported by genetic evidence from Mendelian randomization studies, and there was little evidence that other inflammatory markers like TNFα and IL-6 affected breast cancer risk. These findings suggest that while chronic low-grade inflammation measured by CRP may modestly increase breast cancer risk, the overall role of inflammation in breast cancer development remains unclear, with limited support beyond CRP—highlighting the need for higher-quality prospective studies and mechanistic research to clarify whether inflammation is truly causal or merely a marker of other underlying processes that drive breast carcinogenesis.
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.
2023
Adv Nutr
A systematic review and meta-analysis of 31 studies (29 included in quantitative analysis) following Cochrane methodology examined associations between healthy lifestyle indices (incorporating factors like healthy body weight, diet, physical activity) and breast cancer risk. Comparing the highest versus lowest adherence categories, the analysis found a 20% breast cancer risk reduction in prospective studies (HR=0.80; 95% CI: 0.78-0.83) and 26% reduction in retrospective studies (OR=0.74; 95% CI: 0.63-0.86), with inverse associations remaining significant when stratified by menopausal status (except for premenopausal BC in prospective studies) and across molecular subtypes: ER+/PR+ (HR=0.68; 95% CI: 0.63-0.73), ER+/PR- (HR=0.78; 95% CI: 0.67-0.90), and ER-/PR- (HR=0.77; 95% CI: 0.64-0.92). These findings—with most studies scoring low risk of bias and moderate certainty of evidence—demonstrate that adherence to healthy lifestyles reduces breast cancer risk by approximately 20-30% regardless of molecular subtype or menopausal status, supporting the prioritization of lifestyle-based recommendations for population-level breast cancer prevention as a key modifiable approach to reducing the substantial disease burden.
2022
Cancer Epidemiol
A hospital-based case-control study of 379 histologically confirmed breast cancer cases and 403 controls in Lagos and Abuja, Nigeria (October 2016-May 2017) examined associations between physical activity and breast cancer risk using metabolic equivalent (MET) hours per week across occupational, household, transport, and leisure domains. Women in the upper-middle category of total physical activity had 56% reduced breast cancer risk (AOR=0.44; 95% CI: 0.27-0.78), with particularly strong protective effects for total non-vigorous PA (AOR=0.26; 95% CI: 0.09-0.75), household PA (AOR=0.38; 95% CI: 0.20-0.71), and occupational PA (AOR=0.64; 95% CI: 0.40-1.02), while transport and leisure PA showed no significant associations. These findings—among the first examining physical activity and breast cancer in sub-Saharan Africa—suggest that the cumulative effect of various daily physical activities, particularly household and occupational activities common among Nigerian women, substantially reduces breast cancer risk and should be promoted as part of breast cancer prevention strategies in Nigeria and potentially other low- and middle-income countries where physical activity patterns differ from high-income countries with predominantly leisure-time activity.
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
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 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.
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.
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
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
Int J Mol Sci
The gut microbiome—trillions of bacteria living in the digestive tract—appears to influence breast cancer risk, treatment effectiveness, and likelihood of recurrence through its effects on metabolism, hormones, immune function, and brain signaling. While cancer treatments can disrupt the gut microbiome and contribute to negative side effects, research shows that the microbiome can be positively modified through diet, probiotic and prebiotic supplements, and exercise. This review synthesizes current evidence on the gut-breast cancer connection and highlights practical strategies for improving gut health that may lead to better treatment outcomes, fewer side effects, and improved overall wellbeing for breast cancer patients.
2019
Breast Cancer Res Treat
A case-control study within the MCC-Spain cohort examined 1,389 invasive breast cancer cases and 1,712 controls aged 20-85 years to investigate domain-specific associations between physical activity and breast cancer risk by menopausal status and molecular subtype. The study found unexpected results: occupational physical activity (OPA) intensity was associated with higher breast cancer risk, particularly for premenopausal women (OR = 1.89 for active/very active vs. sedentary jobs) and ER+/PR+, HER2- tumors (OR = 1.80), while sedentary time ≥6 hours/day increased postmenopausal breast cancer risk by 69%; conversely, moderate-to-high intensity household and recreational physical activity above 1,000 MET·min/week reduced breast cancer risk by 14-33% in both pre- and postmenopausal women. These findings reveal important distinctions between types of physical activity: while leisure-time and household physical activity provide protective benefits against breast cancer, occupational physical activity paradoxically showed positive associations with breast cancer risk—particularly for hormone receptor-positive tumors—which may reflect different biological mechanisms, exposure patterns, or confounding factors associated with Occupation. The study highlights that sitting time is an independent breast cancer risk factor regardless of other physical activity, and the surprising positive association between occupational physical activity and ER+/PR+ breast cancer warrants further investigation to understand underlying mechanisms.
2019
Sci Rep
A Spanish case-control study of 973 breast cancer patients matched with controls found that the relationship between caloric intake and breast cancer risk varied dramatically by menopausal status: premenopausal women consuming 20% or more below their predicted caloric needs had a 64% reduced risk, while postmenopausal women consuming 40% or more above predicted needs had a 181% increased risk. For every 20% increase in relative caloric intake (observed versus predicted based on individual metabolism and activity), hormone receptor-positive and HER2-positive breast cancer risk increased by 13%, with triple-negative tumors showing a 7% increase per 20% caloric excess. These findings suggest that maintaining appropriate caloric intake matched to individual energy needs—and potentially moderate caloric restriction combined with regular physical activity—could be an effective breast cancer prevention strategy, particularly important given the different effects observed in pre- versus postmenopausal women.
2018
Cancer Epidemiol Biomark Prev
A systematic review and meta-analysis of 24 studies found suggestive evidence that physical activity may reduce breast cancer risk through increased global DNA methylation, with higher activity levels showing a trend toward higher methylation (19% standardized mean difference) and higher methylation associated with a 30% reduced breast cancer risk, though neither association reached statistical significance overall. Subgroup analyses revealed that the protective pathway became clearer when examining long-term physical activity patterns and prospective cohort studies specifically, where both associations were statistically significant. This is the first systematic review to examine the complete biological pathway linking physical activity to breast cancer prevention through epigenetic mechanisms, suggesting that exercise may alter DNA methylation patterns in ways that protect against cancer development—a finding that could help explain how physical activity exerts its well-established cancer-preventive effects at the molecular level.
2018
Biomed Res Int
A case-control study of 116 women with newly diagnosed breast cancer and 226 controls used dual-energy X-ray absorptiometry to examine the relationship between body composition, physical activity, and breast cancer risk, analyzing results separately by menopausal status. In premenopausal women, higher total body fat percentage, android (abdominal) fat, and waist circumference were associated with increased breast cancer risk, while higher lean body mass and greater physical activity were protective; among postmenopausal women, physical activity reduced breast cancer risk by 49%. The study concludes that low lean body mass and high abdominal fat increase breast cancer risk in premenopausal women, while regular physical activity is protective against breast cancer in both pre- and postmenopausal women. These findings suggest that maintaining healthy body composition through physical activity may be an important breast cancer prevention strategy across all life stages.
2018
Breast Cancer Res Treat
A study of 27,153 postmenopausal women in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial created an estrogen-related lifestyle score (ERLS) combining four factors: estrogenic diet, alcohol intake, body mass index (BMI), and physical activity, with scores ranging from 0-6 and higher scores representing lower estrogenic lifestyle patterns. Women with ERLS scores of 4 or ≥5 had 23% and 34% lower breast cancer risk, respectively, compared to those with scores ≤2, with similar protective effects observed for invasive cases and estrogen receptor-positive subtypes. The findings indicate that adopting multiple low-estrogen lifestyle behaviors together—including a low estrogenic diet, minimal alcohol consumption, healthy body weight, and high physical activity—has a combined protective effect against postmenopausal breast cancer that is stronger than any single factor alone. The researchers suggest this combined effect likely works by influencing estrogen metabolism, highlighting the importance of addressing multiple lifestyle factors simultaneously for breast cancer prevention in postmenopausal women.
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.
2022
PLOS Med
A large French study following nearly 103,000 adults for nearly 8 years found that people who consumed higher amounts of artificial sweeteners—particularly aspartame and acesulfame-K found in diet sodas and many processed foods—had a 13-15% increased risk of cancer overall, with specific increases in breast cancer and obesity-related cancers. The research, which carefully tracked detailed dietary records and controlled for multiple lifestyle factors, showed aspartame was associated with a 22% higher breast cancer risk among higher consumers compared to non-consumers. While the study has some limitations including potential confounding factors, these findings add to growing concerns about artificial sweetener safety and support the need for regulatory agencies to re-evaluate the safety of these widely used food additives found in thousands of products worldwide.