According to Kaiser Permanente research, in a long-term national study, breastfeeding for six months or longer the risk of developing type 2 diabetes nearly in half for women throughout their childbearing years. The study findings were published in the JAMA Internal Medicine .

Women who breastfed for six months or more across all births had a 47% reduction in their risk of developing type 2 diabetes compared to those who did not breastfeed at all. Women who breastfed for six months or less had a 25% reduction in diabetes risk.

Dr. Gunderson and colleagues analyzed data on the 30 years of follow-up from the Coronary Artery Risk Development in Young Adults ( CARDIA ) study, that originally enrolled about 5,000 adults aged 18 to 30 in 1985 to 1986, including more than 1,000 members of Kaiser Permanente Northern California.

The new findings add to a growing body of evidence that breastfeeding has protective effects for both mothers and their offspring, including lowering to mother's risk of breast and ovarian cancer.

The CARDIA findings are also consistent with those of the NIH-funded Study of Women, Infant Feeding and Type 2 Diabetes after GDM Pregnancy ( SWIFT ), which includes routine biochemical screening for diabetes in women after gestational diabetes from the early postpartum period and years later .

The long-term benefits of breastfeeding on lower diabetes risk were similar for black and white women, and with and without gestational diabetes.

Black women were three times as likely to develop diabetes within the 30-year study, which is consistent with higher risk. Black women rolled up in CARDIA were also less likely to breastfeed than white women.

This study included 1,238 black and white women who did not have diabetes when they enrolled in CARDIA, or prior to their subsequent pregnancies.

Over the next 30 years, each woman had at least one live birth and was routinely screened for diabetes under the CARDIA protocol , which included diagnostic screening criteria for diabetes. Participants also reported lifestyle behaviors and the total amount of time they breastfed their children.

Unlike previous studies of breastfeeding, which relied on self-reporting of diabetes onset and began to follow older women in later life, researchers were able to follow women during the childbearing period and screen them regularly for diabetes before and after pregnancies.

Gunderson and her colleagues were also able to account for pre-pregnancy metabolic risk, including obesity and fasting glucose and insulin, lifestyle behaviors, family history of diabetes, and perinatal outcomes.