Mysterious Effects of Smoking May Surface Even 3 Generations Later, Study Finds - ScienceAlert

The 2014 analysis of questionnaire data from the Children of the 90s study revealed that the sons of fathers who started smoking before they were 11 years old were more likely to have a higher body mass index (BMI) in adolescence, with increased average waist circumference and whole-body fat mass.

The researchers say a similar effect can be seen even when the intervening generations don't smoke regularly while under 13 years of age, evidencing a transgenerational effect across four generations.

It's possible this is just a correlation somehow, not an effect caused by exposure to tobacco smoke; the researchers acknowledge it's loosely possible that the pre-puberty smokers in the study may have had a hereditary predisposition to obesity that only surfaced a few generations downstream.