Teenager boys who were obese at the age of 18 are one-third more likely to die prematurely compared to their normal weight peers announced Swedish researchers on Wednesday.

A study of more than 45,000 men underlines the dangers of being overweight and the need to tackle the growing problem of childhood obesity. The study also found that teens (both boys and girls) who were obese at the age of 18 are twice as likely to die prematurely.

Currently, the World Health Organization classifies more than 400 million people worldwide as obese, including 20 million children under the age of five.

"Obesity and overweight were as hazardous as heavy and light smoking," Martin Neovius of the Karolinska Institute in Sweden and his colleagues wrote in the British Medical Journal. "The obesity pandemic seems to affect children and adolescents more than adults."