They predict alarming increases in the rates of heart disease and premature death by the time today's teenagers reach young adulthood.
They say as a consequence of this obesity, these young adults can expect to have more heart attacks, more chronic chest pain and more deaths before they reach age 50.
For the Danish study more than one quarter of a million school children in Copenhagen were tracked from 1930 to 1976, and it was found that overweight children grew up to have more heart problems; this was particularly true for boys.
The research revealed that the heavier people were as youngsters, particularly entering their teens, the greater was the risk.
Lead author Jennifer Baker from the Center for Health and Society in Copenhagen says the findings suggest that more children than ever before are facing increased risks of coronary heart disease (CHD) in adulthood.
According to the Centers for Disease Control and Prevention more than 9 million youngsters in the U.S. are now overweight.
The researchers from the University of California, San Francisco (UCSF) say 25 percent the boys in that number are obese, and that is expected to increase to 30 to 37 percent by 2020, when they reach 35; while for females 32 percent of that number are now obese and that ratio will rise to 34 to 44 percent.
The researchers used a computer-based statistical modeling system to estimate the potential impact of an increasingly overweight U.S. adolescent population on future adult health nationwide.
According to the researchers more heart disease, diabetes and high blood pressure will be seen at a younger age and even aggressive treatment will not be able to stem the trend.
The research team, led by Dr. Kirsten Bibbins-Domingo, an assistant professor in medicine, epidemiology and biostatistics at UCSF, say unless something is done, current adolescent overweight will have a substantial effect on public health far into the future.
The model estimated more than 100,000 extra cases of heart disease by 2035, which is a 16 percent increase over today ™s figures, and a rise in obesity-related CHD deaths by as much as 19 percent.
Dr. Bibbins-Domingo says one of the major health risks for an obese person is becoming diabetic; diabetes increases the risk of heart disease and many other health complications and it is very difficult to lower the likelihood of getting diabetes once a person is obese.
Experts agree and say childhood obesity may shorten life expectancy in the United States by 2 to 5 years by 2050 which equates to the effect of all cancers combined, with catastrophic effects in terms of costs, diminished productivity and physical and psychological disabilities.
The studies are published in the New England Journal of Medicine.