KEEPING fit as a teenager can halve the risk of heart attacks much later in life, a study has found.

Every 15% increase in fitness at 18 cuts the chances of a heart attack 30 years later by almost a fifth, according to scientists who studied data on more than 743,000 national service conscripts in Sweden.

But the study also showed that fitness could not counteract the effects of being overweight or obese, which greatly increased heart attack risk.

All the participants underwent fitness tests at the age of 18 prior to entering the Swedish armed forces between 1969 and 1984, before Sweden dropped compulsory national service in 2010.