Approximately nine million women in the U.S. have type 2 diabetes . A number of lifestyle factors, including diet, exercise, and obesity, can affect the risk of developing type 2 diabetes. In addition, breastfeeding has been associated with improved insulin sensitivity and glucose tolerance—both of which protect against diabetes. But until now, no study has directly studied the relationship between breastfeeding and risk of actually developing type 2 diabetes.

A new study in the November 23/30, 2005 issue of the Journal of the American Medical Association followed over 150,000 women who had given birth and found that those who had breastfed longer had a lower risk of developing type 2 diabetes.

About the Study

Researchers from Brigham and Women’s Hospital and Harvard Medical School in Boston examined data on 157,003 women from the Nurses’ Health Studies, which followed a group of female nurses for at least 10 years. The women completed health and medical questionnaires every two years. In addition, they reported how many months they had ever breastfed. The researchers adjusted their analyses for other factors known or thought to affect diabetes risk, including body mass index (BMI, a measure of weight in relation to height), diet, exercise, and smoking.

In women who had given birth in the previous 15 years, each additional year of breastfeeding was associated with a 15% reduced risk of developing type 2 diabetes. There was no association between breastfeeding and type 2 diabetes in women who had given birth more than 15 years ago.

These findings are limited because the researchers relied on the women’s self-reported duration of breastfeeding, and it is possible that they breastfed for a longer or shorter time than reported.

How Does This Affect You?

These results indicate that breastfeeding may reduce the risk of developing type 2 diabetes. And it seems breastfeeding for longer durations increases the protective effect. In fact, the researchers estimate that the beneficial effects begin to take place after six months of breastfeeding.

The results of this and many other studies strongly support the many benefits of breastfeeding. If you’re pregnant, plan on breastfeeding if you can. The American Academy of Pediatrics recommends that mothers breastfeed their infants for at least one year because of its beneficial effects on growing infants. This study suggests that breastfeeding will not only benefit your baby’s health— but yours, as well.