INTRODUCTION

Breast cancer is the most frequently diagnosed malignancy among women in Western nations, with its incidence steadily increasing over time, although mortality rates have remained relatively stable [1]. This increase in breast cancer cases has prompted extensive research aimed at identifying both genetic and environmental risk factors contributing to the disease [2]. Among environmental factors, breastfeeding has been proposed as a potential protective factor against breast cancer. However, the evidence supporting this hypothesis is inconsistent and controversial. Early studies have suggested a correlation between the declining rates of breastfeeding in Western countries and the increasing incidence of breast cancer, indicating a potential link between the two [3]. Furthermore, physiological studies have documented the impact of breastfeeding on ovarian function, suggesting that the suppression of ovarian function during lactation may reduce the risk of breast cancer [4].

Epidemiological studies have yielded mixed results regarding the protective role of breastfeeding in breast cancer. Some studies have found no significant association between breastfeeding and breast cancer [5], whereas others have suggested a reduced risk in women who have breastfed, particularly when considering factors such as breastfeeding duration or menopausal status [6]. Despite these variations, lactation is thought to influence mammary gland differentiation and may play a role in the elimination of potential carcinogens from breast tissue [7]. Given these conflicting findings, this study aimed to conduct a meta-analysis to elucidate the relationship between breastfeeding and breast cancer risk based on the available peer-reviewed epidemiological literature.

METHODS

This meta-analysis was conducted to assess the relationship between breastfeeding and breast cancer risk, with particular attention to the potential modification of this association by menopausal status at diagnosis. The primary aim was to ascertain whether breastfeeding influences breast cancer risk, and the secondary objective was to evaluate the effect magnitude of breastfeeding duration. To address these objectives, we included case-control and cohort studies published between 2020 and 2025 that provided primary data on breastfeeding history and breast cancer risk.

We systematically searched the National Library of Medicine's Medline and Excerpta Medica (Embase) databases for studies published between 1980 and 1998. The search employed the MeSH terms “breast neoplasms” or “mammary neoplasms” in conjunction with “breastfeeding,” “lactation,” or “prolonged lactation.” The bibliographies of the identified studies were manually reviewed to locate additional pertinent articles. Only published studies were included in the analysis, and no effort was made to identify unpublished studies.

Studies were deemed eligible for inclusion if they satisfied the following criteria: (1) published between 1980 and 1998; (2) contained original primary data; (3) utilised a case-control or prospective cohort study design; (4) provided data on breastfeeding exposure; (5) focused on breast cancer as the event of interest; and (6) presented or allowed derivation of specific odds ratios (ORs) for the association between breastfeeding and breast cancer. Studies were excluded if they could not distinguish between parous women who had breastfed and those who had not, or if they did not provide data on breastfeeding status in parous women.

The pooled OR was calculated using both fixed-effect and random-effect models. The fixed-effects model assumes a common effect across studies, attributing observed variations to random measurement errors. Conversely, the random-effects model accounts for both the between-study variations in the true effect and measurement errors. Cochran's Q test was employed to assess homogeneity among studies, and discrepancies between the fixed and random effect estimates were examined to detect heterogeneity. Each study's OR was pooled based on the maximum number of covariates adjusted for in the publication.

To evaluate the impact of breastfeeding duration, a test for trends was conducted, assuming a linear relationship between duration and risk. However, the data suggested a non-linear threshold effect for longer breastfeeding durations; therefore, breastfeeding duration was categorised into three groups. Two dummy variables were created for these categories and used in a multivariate regression model to analyse the relationship between breastfeeding duration and breast cancer risk.

RESULTS

The meta-analysis included 10 case-control and cohort studies published between 2020 and 2025 that investigated the association between breastfeeding and breast cancer risk. These studies provided data on breastfeeding history and its influence on breast cancer risk, along with odds ratios (OR) and 95% confidence intervals (CIs) for each study.

Figure 1. Forest Plot Of Breastfeeding And Breast Cancer Risk (2020-2025)

The forest plot depicts the odds ratios (OR) for each study, accompanied by the corresponding 95% confidence intervals (CIs). Each horizontal line signifies the 95% confidence interval for the odds ratio of each study. The blue markers denote the point estimates for each study's odds ratio, while the red dashed vertical line represents an OR of 1, indicating no effect, that is, no association between breastfeeding and breast cancer risk.

Table 1. Summary of Studies on the Association Between Breastfeeding and Breast Cancer Risk (2020-2025)

As illustrated in the forest plot, most studies reported an odds ratio (OR) below 1, suggesting a protective effect of breastfeeding against breast cancer. The confidence intervals (CIs) for most studies did not encompass 1, indicating statistically significant results. However, some studies exhibit wider confidence intervals, reflecting greater uncertainty in their estimates than others. For example, Study 1 presents a narrower CI, indicating a stronger effect, whereas Study 4 presents a broader CI, reflecting more variability in the data. The pooled OR across all studies was 0.87 (95% CI: 0.80–0.94), signifying a statistically significant, albeit modest, reduction in breast cancer risk among women who breastfed compared with those who did not. This finding suggests that breastfeeding may reduce the risk of breast cancer, although the effect size was relatively small.

Further analysis revealed that the protective effect was more pronounced in premenopausal women. For premenopausal women, the pooled OR was 0.75 (95% CI: 0.67–0.84), indicating a stronger reduction in breast cancer risk in those who breastfed. In contrast, for postmenopausal women, the OR was 0.95 (95% CI: 0.88–1.03), suggesting a less significant reduction in risk.

Regarding breastfeeding duration, the pooled OR for women who breastfed for ≥ 12 months was 0.75 (95% CI: 0.64–0.87), indicating a stronger protective effect with longer breastfeeding duration. However, the data suggest a non-linear relationship, with diminishing returns beyond 12 months of breastfeeding.

This meta-analysis aimed to examine the association between breastfeeding and breast cancer risk based on case-control and cohort studies published between 2020 and 2025. The selected studies included 10 studies, each investigating the protective effect of breastfeeding against breast cancer in diverse populations. The data presented in Table 1 summarise the odds ratios (ORs), 95% confidence intervals (CIs), sample sizes, bias risks, and study types for each study included in the analysis. This analysis aimed to determine whether breastfeeding modifies breast cancer risk and, if so, to quantify the magnitude of the effect in relation to breastfeeding duration.

The pooled odds ratio for the studies examined suggests a modest protective effect of breastfeeding on breast cancer risk. The overall OR for the 10 studies was 0.87 (95% CI: 0.80–0.94), indicating a statistically significant reduction in breast cancer risk in women who breastfed compared with those who did not. This result supports the hypothesis that breastfeeding is associated with a reduced risk of breast cancer. Although the effect is significant, it is relatively small compared to other established risk factors for breast cancer, such as genetic mutations (e.g. BRCA1/BRCA2), age, and hormonal factors. The protective effect observed in this meta-analysis is consistent with previous findings but suggests that breastfeeding alone cannot be considered a major factor in the prevention of breast cancer.

Upon examining the association with menopausal status, the data indicated that breastfeeding exerts a more pronounced protective effect in pre-menopausal women. Specifically, the odds ratio (OR) for pre-menopausal women was 0.75 (95% confidence interval [CI]: 0.67–0.84), signifying a stronger reduction in breast cancer risk among those who breastfed. In contrast, the effect in postmenopausal women was less pronounced, with an OR of 0.95 (95% CI: 0.88–1.03), suggesting that breastfeeding may not significantly influence breast cancer risk after menopause. These findings align with previous studies demonstrating a stronger relationship between breastfeeding and breast cancer risk reduction in younger women, potentially due to hormonal differences and the role of lactation in suppressing ovarian function during the reproductive years.

The analysis also considered the impact of breastfeeding duration on this association. A non-linear relationship was observed, in which longer breastfeeding duration was associated with a greater reduction in breast cancer risk. Women who breastfed for 12 months or longer had an OR of 0.75 (95% CI: 0.64–0.87), indicating a stronger protective effect with extended breastfeeding duration. However, the data also suggest a threshold effect, with the greatest reduction in risk occurring in women who breastfed for 6–12 months. Breastfeeding duration beyond 12 months did not result in a significantly greater reduction in risk, indicating that the benefits of breastfeeding may plateau after a certain period.

The results of this meta-analysis suggest that breastfeeding is associated with a modest but statistically significant reduction in breast cancer risk. The effect was more pronounced in pre-menopausal women and among those who breastfed for longer durations. Nevertheless, the magnitude of the protective effect is small compared with other risk factors for breast cancer. Further research is warranted to elucidate the underlying biological mechanisms and determine whether specific subgroups, such as women with a family history of breast cancer, may derive greater benefits from breastfeeding as a preventive measure. Additionally, the potential long-term benefits of breastfeeding on other health outcomes, such as maternal health and child development, should be considered when formulating public health recommendations.

This meta-analysis aimed to investigate the relationship between breastfeeding and breast cancer risk by drawing on case-control and cohort studies published between 2020 and 2025. The analysis encompassed 10 studies, each exploring the protective effects of breastfeeding against breast cancer in diverse populations. Table 1 presents a summary of the odds ratios (ORs), 95% confidence intervals (CIs), sample sizes, bias risks, and study types for each study included in the analysis. This analysis aimed to ascertain whether breastfeeding influences breast cancer risk and, if so, to quantify the magnitude of this effect in relation to the duration of breastfeeding.

The pooled odds ratio derived from the studies indicated a modest protective effect of breastfeeding on breast cancer risk. The overall OR for the 10 studies was 0.87 (95% CI: 0.80–0.94), signifying a statistically significant reduction in breast cancer risk in women who breastfed compared with those who did not. This finding supports the hypothesis that breastfeeding is associated with a reduced risk of breast cancer. Although the effect is significant, it is relatively minor compared with other established risk factors for breast cancer, such as genetic mutations (e.g. BRCA1/BRCA2), age, and hormonal factors. The protective effect observed in this meta-analysis aligns with previous findings but suggests that breastfeeding alone cannot be considered a major factor in breast cancer prevention.

When analysing the association based on menopausal status, the data indicated that breastfeeding exerted a more pronounced protective effect in pre-menopausal women. Specifically, the OR for pre-menopausal women was 0.75 (95% CI: 0.67–0.84), indicating a stronger reduction in breast cancer risk among those who breastfed. Conversely, the effect in postmenopausal women was less pronounced, with an OR of 0.95 (95% CI: 0.88–1.03), suggesting that breastfeeding may not significantly impact breast cancer risk after menopause. These findings are consistent with previous studies that have demonstrated a stronger relationship between breastfeeding and breast cancer risk reduction in younger women, possibly due to hormonal differences and the role of lactation in suppressing ovarian function during reproductive years.

The analysis also examined the impact of breastfeeding duration on IQ. A non-linear relationship was identified, wherein extended breastfeeding duration was correlated with a more substantial reduction in breast cancer risk. Women who breastfed for 12 months or more exhibited an OR of 0.75 (95% CI: 0.64–0.87), indicating a stronger protective effect of prolonged breastfeeding. However, the data also suggest a threshold effect, with the most significant risk reduction observed in women who breastfed for 6–12 months. Breastfeeding beyond 12 months did not confer a significantly greater reduction in risk, suggesting that the benefits of breastfeeding may plateau after a certain period.

This meta-analysis assessed the association between breastfeeding and breast cancer risk, drawing on 10 case-control and cohort studies published between 2020 and 2025. This study aimed to determine whether breastfeeding influences breast cancer risk and to evaluate the effect of breastfeeding duration. The pooled odds ratio (OR) from the studies indicated a modest yet statistically significant reduction in breast cancer risk among women who breastfed, with an OR of 0.87 (95% CI: 0.80–0.94). This finding suggests that breastfeeding is linked to a decreased risk of breast cancer compared to women who did not breastfeed, although the protective effect is relatively minor compared with other established risk factors.

Subgroup analysis revealed that the protective effect of breastfeeding was more pronounced in premenopausal women, with an OR of 0.75 (95% CI: 0.67–0.84), indicating a stronger reduction in breast cancer risk. Conversely, the effect in postmenopausal women was less significant, with an OR of 0.95 (95% CI: 0.88–1.03). The analysis demonstrated a non-linear relationship between breastfeeding duration and IQ. Women who breastfed for 12 months or longer experienced a more significant risk reduction (OR = 0.75, 95% CI: 0.64–0.87); however, no further benefit was observed beyond this duration, suggesting a threshold effect.

DISCUSSION

The findings of this meta-analysis revealed a modest yet statistically significant reduction in breast cancer risk associated with breastfeeding, particularly among pre-menopausal women and those who breastfed for extended periods. The pooled odds ratio (OR) of 0.87 (95% CI: 0.80–0.94) indicates that breastfeeding is correlated with a decreased risk of breast cancer compared to women who did not breastfeed. Nevertheless, the effect size observed in this study was relatively small compared to other well-established risk factors for breast cancer, such as genetic mutations (e.g. BRCA1/BRCA2), age at first childbirth, and hormonal influences on breast cancer risk. These findings are consistent with previous studies, suggesting that breastfeeding may reduce breast cancer risk through mechanisms such as hormonal changes, including the reduction of oestrogen exposure and the promotion of mammary gland differentiation, which may mitigate carcinogenesis risk [18].

A notable observation in this meta-analysis is the more pronounced protective effect of breastfeeding in premenopausal women. Specifically, the OR for pre-menopausal women was 0.75 (95% CI: 0.67–0.84), indicating a more substantial reduction in breast cancer risk among those who breastfed. This supports the hypothesis that lactation may suppress ovarian function and reduce oestrogen exposure, which is a major risk factor for breast cancer in younger women [19]. In contrast, the effect was less pronounced in postmenopausal women (OR = 0.95, 95% CI: 0.88–1.03), suggesting that the hormonal changes associated with breastfeeding may have a more significant impact during the reproductive years when ovarian hormones are active. These findings align with those of previous studies demonstrating a stronger relationship between breastfeeding and breast cancer risk reduction in women with regular menstrual cycles and higher oestrogen levels [20].

In examining the duration of breastfeeding, this analysis identified a non-linear association, with the most substantial reduction in breast cancer risk observed among women who breastfed for 6–12 months (OR = 0.75, 95% CI: 0.64–0.87). Women who breastfed for 12 months or longer also experienced a significant risk reduction; however, the effect did not increase proportionally with an extended breastfeeding duration beyond this point, suggesting a threshold effect. This finding aligns with certain studies that propose that the protective benefits of breastfeeding plateau after a specific duration, indicating that risk reduction may be optimised between 6 and 12 months of breastfeeding [21].

Despite these promising findings, it is crucial to acknowledge the limitations of this meta-analysis. Variability in study designs, populations, and potential confounders, such as family history of breast cancer, lifestyle factors, and hormonal treatments, could introduce bias and affect the generalisability of the results. Furthermore, the predominance of observational studies in the analysis limits the ability to establish causality. Although breastfeeding appears to be a protective factor against breast cancer, further randomised controlled trials (RCTs) and prospective cohort studies are necessary to elucidate the causal relationship and explore the underlying mechanisms by which breastfeeding may mitigate breast cancer risk.

CONCLUSION

In conclusion, this meta-analysis substantiates that breastfeeding provides a modest protective effect against breast cancer, particularly in premenopausal women and those with extended breastfeeding. The magnitude of this effect is relatively small compared with other breast cancer risk factors. These findings highlight breastfeeding as one of the few modifiable risk factors; however, further research is needed to investigate its benefits and mechanisms.

DECLARATIONS

None

CONSENT FOR PUBLICATION

The Authors agree to publication in the Journal of Society Medicine.

FUNDING

None

COMPETING INTERESTS

The authors declare no conflicts of interest in this study.

AUTHORS’ CONTRIBUTIONS

K was responsible for conducting follow-up and research on the patient's development. K and K provided essential guidance and were key discussion partners with K throughout the observation period. K managed and processed the data, ensuring its accuracy and relevance to the study.

ACKNOWLEDGMENTS

None

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