There was a 14-15 percent reduced risk of type II diabetes among women for each additional year that they breastfed, a recent large analysis found.

Type 2 diabetes mellitus, which affects about 9 million adult women in the US, imposes a considerable burden on the healthcare system. The disease and its complications absorb $1 of every $10 spent. Multiple lifestyle factors, including poor diet, insufficient exercise and obesity, are associated with risk of diabetes.

Women who are breastfeeding show Improved insulin sensitivity and glucose tolerance compared to nonlactating mothers, previous studies have shown. Although these and other findings have suggested that breastfeeding may reduce future risk of type 2 diabetes, no prior study has directly examined this link.

Past 15 Years

Alison M. Stuebe, MD, of Brigham and Women’s Hospital and Harvard Medical School, Boston, and colleagues studied the association between lactation duration and development of type 2 diabetes.

The researchers analyzed data on 83,585 women who had given birth who were part of the Nurses' Health Study (NHS), as well as 73,418 women who had given birth who were in the Nurses' Health Study II (NHS II).

Among the women in the NHS, 5,145 cases of type 2 diabetes were diagnosed between 1986 and 2002. In the NHS II, 1,132 cases were diagnosed between 1989 and 2001.

There was a 15 percent reduced risk of diabetes among women in the NHS and 14 percent reduced risk among those in the NHS II for each additional year of breastfeeding, according to analyses that were restricted to women who reported a birth in the past 15 years. The researchers made adjustments to control for current body mass index and other relevant risk factors for type 2 diabetes.

However, there was no association between duration of lactation and type 2 diabetes in the NHS II, and a substantially reduced association in the NHS, among women who reported their last birth more than 15 years ago.

Physiologic Mechanisms

"In conclusion, increased duration of breastfeeding was associated with reduced risk of type 2 diabetes in 2 large cohorts of women," say the authors.

"Together with clinical evidence of improved glucose homeostasis [equilibrium] in lactating women," they continue, "these data suggest that lactation may reduce the risk of type 2 diabetes in young and middle-aged women."

The authors note that further clinical studies are needed to confirm their finding "and to elucidate the physiologic mechanisms for an inverse association between duration of breastfeeding and risk of type 2 diabetes."