Stuebe AM et al. (2005) Duration of lactation and incidence of type 2 diabetes. JAMA 294: 2601–2610

Many studies have demonstrated that lactation is associated with improved insulin sensitivity and glucose tolerance. The link between maternal lactation and risk of type 2 diabetes, however, is not yet clear.

Stuebe et al., therefore, studied the association between lactation and risk of type 2 diabetes in women who took part in the Nurses' Health Study (NHS), a prospective observational cohort of 83,585 parous women, and NHS II, a retrospective observational cohort of 73,418 parous women.

In the NHS cohort, there were 5,145 cases of type 2 diabetes during 1,239,709 person-years of follow-up between 1986 and 2002. This compared with 1,132 cases of type 2 diabetes during 778,876 person-years of follow-up between 1989 and 2001, in the NHS II cohort. Both studies showed that greater duration of lactation was associated with a reduced risk of type 2 diabetes in young and middle-aged women. This association was independent of BMI, exercise and smoking status. In women who reported a birth in the previous 15 years, for each additional year of breast-feeding there was a decrease in the risk of diabetes of 15% (95% CI 1–27%) and 14% (95% CI 7–21%) in the NHS and NHS II cohorts, respectively.

The authors conclude that a long duration of lactation might reduce the risk of type 2 diabetes in young and middle-aged women by improving glucose homeostasis, but that further clinical studies are needed to confirm this idea.