Researchers said prolonged breast feeding was linked to the stiffening of the arteries, which is an early symptom of cardiovascular disease. But they say the results of their study do not provide sufficient evidence for women to stop breast feeding - which has many health benefits.
Breast feeding can help a baby fight off infections, and is thought to aid brain development.
It has also been shown to have some benefits for cardiovascular health. A team from the Medical Research Council Childhood Nutrition Research Centre at the Institute for Child Health in London studied 331 adults aged between 20 and 28, born at Cambridge Maternity Hospital between 1969 and 1975. They found those who had been breast fed for longer than four months as babies had stiffer arteries than those who had been breast fed for less than four months, or who had been bottle fed. Every extra two months of breast feeding also led to a rise in cholesterol levels and blood pressure. Studies on primates who were breast fed and then placed on a Western style diet found they absorbed more cholesterol.