Smoking cigarettes before puberty has a lasting impact three generations later, a first-of-its-kind study of the transgenerational effects of smoking has concluded.
The granddaughters and great-granddaughters of men who began smoking before the age of 13 are more likely to have excess body fat, found the study, published last week in Scientific Reports.
“If these associations are confirmed in another dataset or using biomarkers, this will be one of the first human demonstrations of transgenerational effects of an environmental exposure across four generations,” the study authors write.
It's no secret that smoking during pregnancy can have a detrimental impact on future generations – it more than doubles the fetus’s risk of sudden infant death, for example. It has also been linked to autism diagnoses in children whose maternal grandmothers smoked while pregnant, and can affect the growth, strength, and fitness of grandchildren and great-grandchildren of smokers.
However, the hereditary effects of smoking outside of pregnancy are much lesser studied.
The team, from the University of Bristol, used the Children of the 90s study. This study collected data on more than 14,000 individuals born in the former county of Avon in the early 90s.
A 2014 analysis of questionnaire data from the study found that fathers who began smoking before the age of 11 were more likely to have sons, not daughters, with more body fat than expected. Their teenage sons were also more likely to have a higher body mass index and increased waist circumference. Previous studies had found similar evidence of non-genetic signals inherited across generations, but these were mostly conducted in animal models.
The present study expanded on these findings, looking across four generations of humans. While no effects were observed in male descendants this time, they were seen in females.
“We now show that if the paternal grandfather had started smoking pre-puberty, compared with later in childhood (13–16 years), his granddaughters […] had evidence of excess fat mass at two ages [17 and 24],” the authors write.
“When fathers of maternal grandfathers had started smoking pre-puberty, their great-granddaughters […] had excess body fat [at 17 and 24].”
It seems the transgenerational effect is irrespective of the intervening generations: “To determine whether these results were due to the later generations starting to smoke pre-puberty, further analyses omitted those in subsequent generations who had smoked regularly from < 13 years,” the study reads. “The results were similar.”
“This research provides us with two important results. First, that before puberty, exposure of a boy to particular substances might have an effect on generations that follow him,” Professor Jean Golding, lead author of the report, said in a statement.
“Second, one of the reasons why children become overweight may be not so much to do with their current diet and exercise, rather than the lifestyle of their ancestors or the persistence of associated factors over the years.”
The authors do note that the numbers are small and the confidence intervals are wide, so these conclusions should be taken with a pinch of salt until they can be verified in future analyses.
It is also possible, they say, that the observed associations between body fat and previous generations’ smoking habits could be clouded by other factors. Genetics, epigenetics, and other environmental factors, for example, are all linked to obesity and could be contributing here.
Still, “there is much to explore,” Golding added.
“If these associations are confirmed in other datasets, this will be one of the first human studies with data suitable to start to look at these associations and to begin to unpick the origin of potentially important cross-generation relationships.”