OBJECTIVEWe examined the association of lactation duration with incident type 2 diabetes among women with a history of gestational diabetes mellitus (GDM).
RESEARCH DESIGN AND METHODSWe monitored 4,372 women with a history of GDM participating in the Nurses' Health Study II for incident type 2 diabetes over 25 years up to 2017. Lactation history was obtained through follow-up questionnaires to calculate lactation duration. Follow-up blood samples were collected from a subset of these women at median age of 58 years through the Diabetes & Women's Health Study.
RESULTSWe documented 873 incident cases of type 2 diabetes during 87,411 person-years of follow-up. Longer duration of lactation was associated with lower risk of type 2 diabetes for both total lactation (hazard ratio 1.05 [95% CI 0.83-1.34] for up to 6 months, 0.91 [0.72-1.16] for 6-12 months, 0.85 [0.67-1.06] for 12-24 months, and 0.73 [0.57-0.93] for >24 months, compared with 0 months; P-trend 5 0.003) and exclusive breastfeeding (P-trend 5 0.002) after adjustment for age, ethnicity, family history of diabetes, parity, age at first birth, smoking, diet quality, physical activity, and prepregnancy BMI. Longer duration of lactation was also associated with lower HbA 1c , fasting plasma insulin, and C-peptide concentrations among women without type 2 diabetes at follow-up (all adjusted P-trend £0.04).
CONCLUSIONSLonger duration of lactation is associated with a lower risk of type 2 diabetes and a favorable glucose metabolic biomarker profile among women with a history of GDM. The underlying mechanisms and impact on diabetes complications, morbidity, and mortality remain to be determined.As women undergo changes in metabolism to meet the demands of the growing fetus and to prepare for delivery and lactation (1), they often experience deterioration in insulin sensitivity during normal pregnancy (2). Although most women maintain glucose homeostasis by a compensatory increase in insulin secretion (1,3), this compensatory mechanism is insufficient in some women, resulting in gestational diabetes mellitus (GDM), which affects ;5-9% of pregnancies in the U.S. (4,5). Because women with a history of GDM are at higher risk for type 2 diabetes later in life (6,7), it is critical to identify modifiable determinants of type 2 diabetes risk prevention specific for these high-risk women.