The certainty of the evidence is downgraded by heterogeneity (between studies) and upgraded by dose-response gradient.
A systematic review and meta-analysis 2 assessed the effect of breastfeeding on risk of breast carcinoma, ovarian carcinoma, and type 2 diabetes mellitus. Breastfeeding over 12 months was associated with reduced risk of breast and ovarian carcinoma by 26% and 37%, respectively, and with 32% lower risk of type 2 diabetes.
Another systematic review and meta-analysis 3 included a total of 22 studies (17 cohort studies and 5 cross-sectional studies) were included, of which 16 contributed to the meta-analysis. Studies with a longer follow-up showed a graded protective association for lactation and the risk of type 2 diabetes, with a potentially larger risk reduction in women with gestational diabetes than in those without gestational diabetes. Overall, ever versus never lactation was associated with a 27% lower risk of type 2 diabetes (RR 0.73, 95% CI 0.65 to 0.83). Each additional month of lactation was associated with a 1% lower risk of type 2 diabetes (RR 0.99, 95% CI 0.98 to 0.99).
Another systematic review and meta-analysis 4 included 4 studies with a total of 206 204 participants. Breastfeeding for more than 12 months was associated with a relative risk reduction of 30% for diabetes (pooled odds ratio, 0.70, 95% CI 0.62 to 0.78).
Another systematic review and meta-analysis 1 evaluating the association of breastfeeding with maternal risk of cardiovascular disease (CVD) included 8 prospective studies and 1 192 700 parous women. 82% reported having ever breastfed; weighted mean lifetime duration of breastfeeding was 15.6 months. Compared parous women who ever breastfed to those who never breastfed, lower risks were found for CVD (hazard ratio [HR] 0.89, 95% CI 0.83 to 0.95; I²=79%), coronary heart disease (HR 0.86, 95% CI 0.78 to 0.95; I²=80%), stroke (HR 0.88, 95% CI 0.79 to 0.99; I²= 80%), and fatal CVD (HR 0.83, 95% CI 0.76 to 0.92; I²=48%).
A meta-analysis 5 included 27 studies involving 13 907 breast cancer cases. The summary relative risk (RR) of breast cancer for the ever compared with never categories of breastfeeding was 0.61 (95% CI 0.44 to 0.85). An inverse association was also found for the longest compared with the shortest categories of breastfeeding with the risk of breast cancer (RR 0.47, 95% CI 0.37 to 0.60).
Another meta-analysis 6 included 65 studies. The summary relative risk (RR) for breast cancer in parous women who breastfed exclusively was 0.72, (95% CI, 0.58 to 0.90), versus parous women who had never breastfed. For parous women who breastfed in any mode, the RR was lower in both premenopausal women (0.86) and postmenopausal women (0.89).
A meta-analysis 7 included 13 case-control studies (9973 women with ovarian cancer and 13 843 controls). Breastfeeding was associated with a 24% lower risk of invasive ovarian cancer (odds ratio [OR] 0.76, 95% CI 0.71 to 0.80). For a single breastfeeding episode, mean breastfeeding duration of 1 to 3 months was associated with 18% lower risk (OR 0.82, 95% CI 0.76 to 0.88), and breastfeeding for 12 or more months was associated with a 34% lower risk (OR 0.66, 95% CI 0.58 to 0.75).
Date of latest search: 2022-03-07
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