Men who started smoking regularly before the age of 11 had sons who, on average, had 5-10kg more body fat than their peers by the time they were in their teens, according to new research from Children of the 90s.

Men who started smoking regularly before the age of 11 had sons who, on average, had 5-10kg more body fat than their peers by the time they were in their teens, according to new research from Children of the 90s. The researchers say this could indicate that exposure to tobacco smoke before the start of puberty may lead to metabolic changes in the next generation.

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.

The effect was not seen in the sons of men who started smoking after the age of 11, suggesting that the period before the start of puberty is a particularly sensitive period for environmental exposures. This is in line with a prior hypothesis by the authors based on earlier Swedish studies that linked paternal ancestor’s food supply in mid childhood with mortality rates in grandchildren.

Of the 9,886 fathers enrolled in the study, 5,376 (54 per cent) were smokers at some time and, of these, 166 (3 per cent) reported smoking regularly before the age of 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 (recorded using whole-body scans), ranging from an extra 5kg to 10kg between ages 13 and 17.

The research was funded by the UK Medical Research Council (MRC) and is published today [2 April 2014] in the European Journal of Human Genetics.

Speaking about the findings, senior author, Professor Marcus Pembrey said:

‘This discovery of trans-generational effects has big implications for research into the current rise in obesity and the evaluation of preventative measures. It is no longer acceptable to just study lifestyle factors in one generation. We are probably missing a trick with respect to understanding several common diseases of public health concern by ignoring the possible effects of previous generations.’

Professor Tim Spector, Professor of Genetic Epidemiology at King's College London commented:

'Transgenerational effects of environment have been clearly shown in rodents but not in humans. This is a rare study showing transgenerational effects in humans. The data are persuasive but not yet definitive as we need to confirm the same smoking-related epigenetic changes in the kids' DNA. We urgently need more studies like this.'

Professor David Lomas, Chair of the MRC’s Population and Systems Medicine Board, added: