A woman's chances of developing a condition linked to heart disease and diabetes can be dramatically reduced by breastfeeding, according to research.
Scientists in Oakland, California, said the risk of metabolic syndrome could be slashed by up to 56%, depending on the duration of the breastfeeding.
And the effect on women with gestational diabetes - a form of the disease associated with pregnancy - was reduced by between 44% and a huge 86%.
Metabolic syndrome involves a range of harmful symptoms, including unresponsiveness to insulin, high blood pressure and raised cholesterol. It is often a precursor to type 2 diabetes and heart disease and linked to premature death.
The 20-year prospective study was the first to look at the effect of breastfeeding on the likelihood of developing metabolic syndrome.
Previous research had shown that lactating women have improved blood levels of glucose and fats within several weeks after giving birth.
Scientists conducting the new study monitored the health of 704 women recruited at the age of 18 to 30.
Over the 20-year follow-up period there were 120 new cases of post-pregnancy metabolic syndrome.
Study leader Dr Erica Gunderson, from US healthcare providers Kaiser Permanente, said: "The findings indicate that breastfeeding a child may have lasting favourable effects on a woman's risk factors for later developing diabetes or heart disease."