The first study, by scientists in Denmark, found that large children, especially boys, are at an increased risk of coronary disease as adults.
The second, based on a computer model, found that overweight adolescents are at increased risk of heart disease and premature death.
Both studies are published in the New England Journal of Medicine.
Obesity is reaching epidemic proportions around the world. In the U.S.A. scientists suggest that 9 million adolescents (17 per cent of the population) are overweight and 80 percent of overweight adolescents grow up to be obese adults. Childhood obesity rates have tripled since 1970.
Worldwide, children are becoming heavier at younger ages. In the United States, 19 percent of children between the ages of 6 and 11 are overweight in the U.K this figure is already at 30 per cent.
Being overweight or obese puts you at increased risk of heart disease, diabetes and cancer.
The first study looked at a group of almost 277,000 Danish children -- all schoolchildren in Copenhagen -- from 1930 to 1976Out of that initial group, more than 10,200 men and 4,300 women were identified whose childhood body-mass index was measured who had received a diagnosis of coronary heart disease (CHD) or died of CHD as adults.
Boys with a high BMI at 7 to 13 years of age and girls with a high BMI from 10 to 13 years of age had a higher risk of a heart disease in adulthood, the researchers found, suggesting that overweight and obese children have an increased risk of cardiovascular events at as early as 25 years of age."
The second study projected the number of overweight adults based on the number of overweight adolescents in 2000. Using a computer model, it predicted that up to 37 percent of men and 44 percent of women will be obese when these people -- now teenagers -- turn 35 in 2020. This could result in up to 5,000 additional deaths from heart disease and 45,000 heart attacks, cardiac arrests and related events by 2035 among this group of young adults. It would raise the death toll from obesity-related coronary heart disease by 19 percent.