NEW YORK (Reuters Health) - Obese teenagers are more likely than their thinner peers to die of heart disease or certain other ills by the time they are middle-aged, a large study suggests.

Researchers found that among more than 200,000 Norwegians followed from adolescence to middle-age, those who were obese or overweight as teens were three to four times as likely to have died of heart disease.

Similarly, their risks of death from colon cancer or respiratory diseases, such as asthma and emphysema, were two to three times that of adults who had been thinner as teenagers. They were also more likely to have died suddenly.

It's not clear how much of the mortality risk stems from early obesity, per se, according to lead researcher Dr. Tone Bjorge, of the Norwegian Institute of Public Health and the University of Bergen.

Study participants who were obese as teenagers, she told Reuters Health, tended to remain obese into adulthood. Obesity later in life has long been implicated as a risk factor for type 2 diabetes, heart disease and certain cancers, Bjorge noted, whereas the long-term effects of childhood obesity are uncertain.

Regardless, she said, "we believe that our results underscore the importance of preventing adolescent obesity.

The findings, published in the American Journal of Epidemiology, are based on data from 227,000 Norwegian men and women who had their height and weight measured sometime between 1963 and 1975, when they were between the ages of 14 and 19.

They were then followed through 2004, when they were 52 years old, on average. During that time, 9,650 died.

In general, the risks of dying from heart disease, colon cancer or respiratory diseases were elevated among participants who had been the heaviest as teens -- those whose body mass index (BMI) was above the 85th percentile for their age and sex. BMI is the ratio of weight to height. The researchers lacked information on lifestyle factors, such as exercise, diet and smoking habits, so the extent to which unhealthy lifestyle contributed to these findings is unclear.

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