Lifetime duration of lactation and chronic inflammation among middle-aged women with a history of gestational diabetes

Introduction Longer duration of lactation is associated with lower cardiometabolic disease risk, but pathogenic pathways involved in the disease progression are unclear, especially among high-risk women. We aimed to examine the associations of lifetime lactation duration with cardiometabolic biomarkers among middle-aged women with a history of gestational diabetes (GDM). Research design and methods Women with a history of GDM participating in the Nurses' Health Study II, a prospective cohort study, were identified and followed through biennial questionnaires beginning in 1991. Lactation history was asked in three follow-up questionnaires to calculate lifetime duration. In 2012-2014, fasting blood samples were collected through the Diabetes & Women's Health Study to measure inflammatory (C-reactive protein (CRP), interleukin (IL) 6), liver enzyme (alanine aminotransferase, aspartate aminotransferase, and gamma-glutamyl transferase), and lipid biomarkers (total cholesterol, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol). Results At follow-up blood collection, women were at median age 58.2 (95% CI 51 to 65) years and 26.3 (95% CI 15.7 to 34.1) years since GDM index pregnancy. After multiple adjustment including prepregnancy body mass index (BMI), longer duration of lactation was significantly associated with lower CRP (least squares (LS) mean 1.90 mg/L (95% CI 1.47 to 2.45) for 0-month lactation, 1.98 mg/L (95% CI 1.68 to 2.32) for up to 12-month lactation, 1.67 mg/L (95% CI 1.42 to 1.97) for 12-24 month lactation, and 1.39 mg/L (95% CI 1.19 to 1.62) for >24-month lactation; p trend=0.003) and IL-6 (1.25 pg/L (95% CI 0.94 to 1.68), 1.19 pg/L (95% CI 0.99 to 1.42), 1.04 pg/L (95% CI 0.87 to 1.25), and 0.93 pg/L (95% CI 0.78 to 1.11); p trend=0.04). Longer duration of lactation was associated with lower risk for chronic inflammation using CRP 3 mg/L cut-off in middle-aged women (OR 0.81 (95% CI 0.69 to 0.940 per 1-year increase) with multiple adjustment. Conclusions Longer lifetime duration of lactation was associated with favorable inflammatory biomarker concentrations in middle-aged women with a history of GDM. Chronic inflammatory pathways may be responsible for previously reported associations between lactation and long-term risk for cardiometabolic diseases.