The new study is one of the most rigorously designed trials ever to explore the impact of breastfeeding on such risk factors.
Researchers examined data on 704 women who were followed for two decades, starting before their first pregnancy.
Because the women were enrolled in a larger heart disease risk study, the researchers had information on wide range of health and lifestyle factors. None of the women had metabolic syndrome at enrollment, but 120 developed the condition during the 20 years of follow-up.
In the population as a whole, breastfeeding for longer than nine months was associated with a 56% reduction in risk for developing metabolic syndrome during the follow-up period.
In women who developed gestational diabetes during one or more pregnancies, the risk reduction was 86%.