London, Did you start smoking real early, say even before age 11? Get ready to have fatter sons.

Men who started smoking regularly before age 11 had sons who on average had 5-10 kg more body fat than their peers by the time they were in their teenage, according to research.

This could indicate that exposure to tobacco smoke before the start of puberty may lead to metabolic changes in the next generation.

“The effect was not seen in the sons of men who started smoking after age 11, suggesting that the period before the start of puberty is a particularly sensitive period for environmental exposures,” explained professor Marcus Pembrey from University of Bristol.

The effect, although present, was not seen to the same degree in daughters.

Many other factors, including genetic factors and the father's weight, were taken into account but none could explain the change.

In fact, the fathers who started smoking before 11 tended to have lower BMIs (body mass index) on average.

Of the 9,886 fathers enrolled in the study, 5,376 (54 percent) were smokers at some time and, of these, 166 (3 percent) reported smoking regularly before age 11.

When measured at age 13, 15 and 17, the sons of the men in the latter category had the highest BMIs at each time point compared with the sons of men who had started smoking later or who had never smoked.

More precisely, these boys had markedly higher levels of fat mass ranging from an extra 5 kg to 10 kg between ages 13 and 17, said the research published in the European Journal of Human Genetics.