It seems there's yet another reason to breastfeed. The longer women breastfeed, the less likely they are to develop type 2 diabetes mellitus, according to an analysis of over 150,000 women participating in the Nurses' Health Study and the Nurses' Health Study II.

Researchers found that each year of breastfeeding reduces the risk of developing type 2 diabetes by 15%. The proposed mechanism is improved glucose homeostasis.

While the correlation persisted in the study even after controlling for such diabetes risk factors as body mass index, amount of exercise, diet, and smoking, it did weaken with age. It also did not build until after 6 months of lactation, so women who breastfeed for shorter periods may not benefit.

Stuebe AM, Rich-Edwards JW, Willett WC, et al. Duration of lactation and incidence of type 2 diabetes. JAMA. 2005;294:2601-2610.