Men who smoked before hitting puberty are more likely to have fat granddaughters or even great-granddaughters, a study suggests.

University of Bristol researchers have previously shown that fathers who quit smoking early in life are more likely to have overweight children.

They believe that they have now found evidence of the fact that the adverse effects of smoking can be seen in four generations.

Experts reviewed the data of 14,000 women who had signed up for the Children of the Nineties Study, which was established to monitor their health and that of their grandchildren.

These records were lined with information about whether the great-grandfathers of their grandchildren had started smoking at 13 years old or later. 

Academics uncovered a link with increased body fat in granddaughters and great-granddaughters, but not in their male counterparts.

Granddaughters whose paternal grandfathers — on their father’s side — smoked as a child carried, on average, 11.8lbs (5.35kg) more fat when they turned 17 than if their ancestors picked up the habit later in their teens. Their average weight was 13.4lbs (6.9kg) when they turned 24. 

If their paternal grandparents were smoking from young ages, the increases in weight and body mass would be 7.8 lb (3.54 kg) and 12.1 lb (5.49kg), respective.  

These men found the relationship to be specific to sex. They suggested smoking might alter your DNA and pass it on to your descendants.

University of Bristol researchers found girls carry 13.4lb (6.1kg) more bodyfat at the age of 24 if their maternal great-grandfathers' smoked before the age of 13 than if they didn't. And they were likely to be 12.1lb (5.49kg) heavier if their paternal grandfathers did so. The effects were the opposite in male descendants for great-grandfathers and they only saw a 4.7lb increase for great-grandfathers

University of Bristol research found that girls have 13.4lb (6.9kg) more body fat at 24 years old if their maternal great grandfathers smoked earlier than 13-years-old. Their paternal grandfathers were more likely to have smoked, and they would be 12.1lb (5.49kg heavier). For male great-grandfathers, the effects were opposite. They only experienced a 4.7lb weight increase.

Graphic shows: Fathers who smoke regularly before they turn 13 produce sons (squares) who are more likely to have excess bodyfat, whereas grandfathers and great-grandfathers who do so are more likely to see the effect in girls (circles)

Graphic: Men who smoke frequently before the age of 13 have more bodyfat than their sons (squares). However, men who smoke more often (great-grandfathers) are less likely to notice any effect on girls (circles).

E-cigarettes can ‘damage men’s fertility’ 

Vaping could damage men’s fertility, a British public health campaign has warned for the first time. 

E-cigarettes are listed alongside smoking, using steroids and drinking too much as factors affecting men’s testicular health and fertility.

British Fertility Society cautioned men to avoid using their laptops on their laps and taking long hot baths. Sperm must be kept cool, so it is best not to. 

Lifestyle changes are partly responsible for the dramatic decline in sperm count in recent years.

A Danish study in 2020 found that vaping men had lower sperm count, while a University College London earlier study showed chemicals found in e-cig flavorings can make swimmers’ sperm slow.

Kevin McEleny, a University of Newcastle male fertility specialist who helped to develop the BFS campaign, said: ‘We know e-cigarette flavourings can be toxic to sperm. 

‘There are real concerns about these devices’ effect on male fertility because they do not go through the same kinds of rigorous checks as drugs do. 

‘I certainly tell men going through IVF that they should not be vaping if possible, although cigarette smoking is likely to be worse.’

However, they didn’t give any clear reasons for it and stated that further studies were needed to prove the connection. 

Previous research by the University of Bergen, Norway, suggested smoking regularly before turning 15 can lead to lower lung function in children and grandchildren — suggesting a similar link of smoking having an effect on genes later down the generations.

Scientific Reports has published the Bristol study. This study used data taken from the Children of the Nineties Study, which was started in 1930 and had its initial intake of 14,000 children join it in September 2012. 

Researchers were unable look at great grandparents and grandmothers, as very few of them smoked during their youth. Because they are more likely to discuss smoking, it made it easier for them to collect data on young male smokers. 

The participants were required to remember their parents and grandparents smoking histories. 

They used that data to determine if previous generations had smoked.

Research showed that the greatest weight differences were observed in those girls whose paternal grandparents and maternal great-grandfathers had smoked, compared with those who hadn’t. 

The findings, which suggest that environmental factors could alter genes in four generations over time, were deemed to be revolutionary by researchers.

Jean Golding (lead author and university epidemiologist) said that the research provided two significant results. 

The first is that a boy’s exposure to certain substances before puberty might have an affect on the generations following him. 

“Second: One reason children are overweight could not be due to their diet or exercise habits, but rather the lifestyles of their ancestors and the persistent effects of these factors throughout the years.

However, the authors acknowledged that their information on prepubescent smoking was not available for men.

It was often claimed that they had done no harm. 

“Nevertheless, even though the rate at which men smoked cigarettes was high in the early part of the 20th century, few people claimed that they started to smoke before age 13. 

“This produced very small numbers to analyze.”

Researchers stated that more research is needed in order to verify the effect of smoking on great-granddaughters and granddaughters before it can be ruled out as a cause.