It is not uncommon to believe that one generation’s exposure to a toxic substance might affect the next generation. You might even say it’s Biblical with stories of sons being punished for the sins of the father. In a recent exploration of transmission down the male line, researchers from the University of Bristol discovered that men who started smoking regularly before the age of 11 had sons who, on average, had 5 to 10 kilograms (about 11 to 22 lbs.) or more body fat than their peers by the time they were in their teens. Oddly, the same trend was not seen in their daughters. “This discovery of trans-generational effects has big implications for research into the current rise in obesity and the evaluation of preventative measures,” said Dr. Marcus Pembrey, professor, School of Social and Community Medicine, and author of the study. “It is no longer acceptable to just study lifestyle factors in one generation.”

In a famous Swedish study, researchers discovered that the paternal grandfather’s food supply in mid-childhood was linked to the mortality rate in his grandsons; surprisingly if the grandfather experienced an overabundance of food during their slow growth period (before puberty), this affected his grandchild’s longevity negatively and worked the other way around when food availability was poor. Considering this Swedish study, the researchers hypothesized that there might be a trans-generational effect from paternal smoking. Specifically, if the father began to smoke during mid-childhood before puberty — the researchers determined this would be before the age of 11 — some health effects would be apparent in their children.

For the current study, the researchers used data from the Avon Longitudinal Study of Parents and Children’s questionnaire, in particular focusing on smoking and age of beginning the habit for fathers as compared to the growth of their children between the ages of 7 and 17. The researchers looked at body mass index (BMI), waist circumference, total fat mass, and lean mass, and compared that to the age at which the father began to smoke regularly.

Of the 9,886 fathers participating in the study, a total of 5,376 (or 54 percent) had been smokers at some time in their life and, of these, 166 (or three percent) reported smoking regularly before age 11. When measured at ages 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. In fact, measuring the boys with whole body scans, they were found to have markedly higher levels of fat mass, ranging from an extra 5 kilograms (11 lbs.) to 10 kilograms (22 lbs.) between ages 13 and 17. Yet the researchers found no significant link between BMI increases and daughters, though the girls were found to have a reduction in total lean mass.

“Our results highlight the importance of the developmental timing of the paternal exposure as well as gender differences in offspring outcomes,” wrote the authors at the conclusion of their study. “Smoking by boys in mid-childhood may contribute to obesity in adolescent boys of the next generation.”

Source: Northstone K, Golding J, Smith GD, Miller LL, Pembrey M. Prepubertal start of father's smoking and increased body fat in his sons: further characterisation of paternal transgenerational responses. European Journal of Human Genetics. 2014.