Scientists have found further evidence that being breast-fed reduces a person's risk of developing heart disease as an adult.
Health experts say breastfeeding is best for mother and baby
Institute of Child Health researchers examined over 200 teenagers whose feeding had been studied as babies.
The study, published in the Lancet, found those who were breast-fed had healthier cholesterol levels than those who were bottle-fed with formula milk.
It was also linked to reduced levels of a protein linked to clogged arteries.
The findings add to earlier research which suggested breast milk could help protect against the condition, known as atherosclerosis.
But most studies have been retrospective. This latest piece of research looked at a group of teenagers who had already been studied as premature babies.
They had been randomly assigned to be fed with either breast milk, standard formula milk or preterm formula.
The researchers then re-examined the teenagers when they were aged 13 to 16.
They took blood samples and looked at the teenagers' ratio of "bad" LDL cholesterol to "good" HDL cholesterol.
It was found those who had been given breast milk during infancy had a significantly lower ratio of bad to good cholesterol than those given formula milk, reducing their risk of developing heart disease.
They also examined concentrations of c-reactive protein (CRP). Higher concentrations are associated with the development of atherosclerosis.
Teenagers who had been breast-fed had lower concentrations of CRP than those who had been given formula.
Factors such as birth weight, teenage weight and social class did not differ between breast and bottle-fed groups.
Writing in the Lancet, Dr Atul Singhal, who led the study, said: "Our findings suggest that breast milk feeding has a major beneficial effect on long-term cardiovascular health".
The team suggest that this could be because breast-fed babies grow more slowly than those who are bottle-fed.
Rapid early growth "programmes" a baby's biology, they said, making it prone to certain health conditions which increase the risk of developing heart disease and stroke, including obesity, high blood pressure, high cholesterol and a tendency to diabetes.
Professor Alan Lucas, director of the Medical Research Council's Childhood Nutrition Research Centre, said: "The evidence is very strong and supports a clear message.
"Slower growth as a baby reduces the risk of heart disease and stroke in adult life, and the best way to achieve this is to breast-feed."
Belinda Phipps, chief executive of the National Childbirth Trust, said: "We know that breast-fed babies are less likely to be overweight and have less chance of developing diabetes in childhood for example but this research also suggests that breastfeeding can have a major beneficial effect on health in later life too.
"Conversely, formula milk has been linked with a higher incidence of respiratory disease, high blood pressure, ear and urinary tract infections, diarrhoea and gastroenteritis."
A recent survey of 1,000 women by the Department of Health found that although the benefits of breast-feeding are well known, the UK has one of the lowest breast-feeding rates in Europe.
Almost a third of women in England and Wales never try to breast-feed, compared to 2% in Sweden.
The research comes as the International Baby Food Action Network (IBFAN) warned efforts to increase breast-feeding rates were being hampered by formula milk companies promoting "misleading" claims.
It said many companies promoted milk substitutes by saying they could make babies more intelligent or were very similar to breast milk.
Professor Jeremy Pearson, Associate Medical Director of the British Heart Foundation, said: "This study is likely to be of considerable scientific and practical importance.
"It provides very strong evidence that babies fed breast milk rather than a formula diet will grow up to have significantly lower levels of LDL cholesterol.
"These findings considerably strengthen the view that nutrition in the womb and in newborn children has a substantial influence on the risk of CHD in later life.
"The study emphasises the need for increased public awareness that the factors leading to CHD operate from early life."