Objectives

Lactation may influence future progression to type 2 diabetes after gestational diabetes mellitus (GDM). However, biomarkers associated with progression to glucose intolerance have not been examined in relation to lactation intensity among postpartum women with previous GDM. This study investigates whether higher lactation intensity is related to more favorable blood lipids, lipoproteins and adipokines after GDM pregnancy independent of obesity, socio-demographics and insulin resistance.

Methods

The Study of Women, Infant Feeding, and Type 2 Diabetes (SWIFT) is a prospective cohort study that recruited 1035 women diagnosed with GDM by the 3-h 100g oral glucose tolerance tests (OGTTs) after delivery of a live birth in 2008-2011. Research staff conducted 2-h 75 g OGTTs, and assessed lactation intensity, anthropometry, lifestyle behaviors and socio-demographics at 6-9 weeks postpartum (baseline). We assayed fasting plasma lipids, lipoproteins, non-esterified free fatty acids, leptin and adiponectin from stored samples obtained at 6-9 weeks postpartum in 1007 of the SWIFT participants who were free of diabetes at baseline. Mean biomarker concentrations were compared among lactation intensity groups using multivariable linear regression models.

Results

Increasing lactation intensity showed graded monotonic associations with fully adjusted mean biomarkers: 5%-8% higher high-density lipoprotein cholesterol (HDL-cholesterol), 20%-28% lower fasting triglycerides, 15%-21% lower leptin (all trend P-values < 0.01), and with 6% lower adiponectin, but only after adjustment for insulin resistance (trend P-value = 0.04).

Conclusion

Higher lactation intensity was associated with more favorable biomarkers for type 2 diabetes, except for lower plasma adiponectin, after GDM delivery. Long-term follow-up studies are needed to assess whether these effects of lactation persist to predict progression to glucose intolerance.

Background

Lactation improves glucose metabolism, but its role in preventing type 2 diabetes mellitus (DM) after gestational diabetes mellitus (GDM) remains uncertain.

Objective

To evaluate lactation and the 2-year incidence of DM after GDM pregnancy.

Design

Prospective, observational cohort of women with recent GDM. (ClinicalTrials.gov: NCT01967030).

Setting

Integrated health care system.

Participants

1035 women diagnosed with GDM who delivered singletons at 35 weeks' gestation or later and enrolled in the Study of Women, Infant Feeding and Type 2 Diabetes After GDM Pregnancy from 2008 to 2011.

Measurements

Three in-person research examinations from 6 to 9 weeks after delivery (baseline) and annual follow-up for 2 years that included 2-hour, 75-g oral glucose tolerance testing; anthropometry; and interviews. Multivariable Weibull regression models evaluated independent associations of lactation measures with incident DM adjusted for potential confounders.

Results

Of 1010 women without diabetes at baseline, 959 (95%) were evaluated up to 2 years later; 113 (11.8%) developed incident DM. There were graded inverse associations for lactation intensity at baseline with incident DM and adjusted hazard ratios of 0.64, 0.54, and 0.46 for mostly formula or mixed/inconsistent, mostly lactation, and exclusive lactation versus exclusive formula feeding, respectively (P trend = 0.016). Time-dependent lactation duration showed graded inverse associations with incident DM and adjusted hazard ratios of 0.55, 0.50, and 0.43 for greater than 2 to 5 months, greater than 5 to 10 months, and greater than 10 months, respectively, versus 0 to 2 months (P trend = 0.007). Weight change slightly attenuated hazard ratios.

Limitation

Randomized design is not feasible or desirable for clinical studies of lactation.

Conclusion

Higher lactation intensity and longer duration were independently associated with lower 2-year incidences of DM after GDM pregnancy. Lactation may prevent DM after GDM delivery.

Primary funding source

National Institute of Child Health and Human Development.