Duration of lactation is associated with lower prevalence of the metabolic syndrome in midlife--SWAN, the study of women's health across the nation.

OBJECTIVE The objective of the study was to evaluate whether lactation duration is associated with lower prevalence of metabolic syndrome (MetSyn) in midlife, parous women. STUDY DESIGN This was a cross-sectional cohort analysis of 2516 parous, midlife women using multivariable logistic regression to determine the independent association of lactation and lactation duration on prevalence of MetSyn. RESULTS One thousand six hundred twenty women (64.4%) reported a history of breast-feeding, with average lifetime duration of lactation of 1.16 (+/- 1.04) years. MetSyn was present in 536 women (21.3%). Adjusting for age, smoking history, parity, ethnicity, socioeconomic status, study site, physical activity, caloric intake, and high school body mass index, women with prior lactation had significantly lower odds of MetSyn (odds ratio [OR] 0.79, 95% confidence interval [CI] 0.63 to 0.99). Furthermore, increasing duration of lactation was similarly associated with lower odds of MetSyn (OR 0.88, 95% CI 0.77 to 0.99). CONCLUSION Duration of lactation is associated with lower prevalence of MetSyn in a dose-response manner in midlife, parous women.