Over the years, countless studies have documented the harmful effects that smoking can have on one’s health. But new research suggests that the threats posed by smoking can have consequences which are more far-reaching and long-term than one could have ever imagined, with the health hazards likely to be passed on to the next few generations.

In other words, people’s smoking habits can have harmful effects not just on themselves, but also on their grandchildren and great-grandchildren.

These are the findings of a study called ‘Children of the 90s’, which was carried out at the University of Bristol in the UK. The results of the recent study were published in the journal Scientific Reports last week.

The ‘Children of the 90s’ project

As a part of the project, researchers have over a period of about 30 years collected 1.5 million samples, including participants’ blood, urine, placenta, teeth, hair and nails. The aim was to assess the environment and genetic factors that affect an individual’s health and development.

About 2,200 papers have been published using data collected due to the project. Some insights have been fascinating, such as the finding that the lines on a baby’s teeth can help determine their risk of developing depression, or how watching TV is linked to an increased risk of asthma.

Some of the findings are intriguing to say the least—for instance, the study states, what you eat as a three-year-old can affect school performance many years later, and anxious pregnant women are more likely to have asthmatic children among a variety of other linkages.

Even so, not everything is connected in a cause-and-effect manner all the time. For instance, a 2013 study of 4,000 pairs of mothers and children showed that maternal Vitamin D deficiency during pregnancy was not associated with the child’s bone health.

The crux of the recent study

The results of this recent study show that the ill-effects of smoking are not limited to an individual’s personal health, but can show up in their offspring as well. Only grandfathers and great-grandfathers were involved since very few grandmothers and great-grandmothers claimed to smoke before puberty.

A crucial finding of this study is that those women, whose paternal grandfathers and great-grandfathers began smoking before puberty, reported the presence of increased body fat.

Specifically, higher body fat was noticed in women whose grandfathers and great-grandfathers had started smoking before the age of 13 years compared to those whose ancestors started smoking later (between 13-16 years of age).

What’s baffling about these observations is that the increased body fat was found only in granddaughters and great-granddaughters. No effects were seen in the grandsons or great-grandsons.

Explaining the findings

A possible explanation is that the pre-puberty smokers had some other features, such as hereditary predisposition to obesity, that might explain why their offspring had excess amounts of body fat. But this does not offer a complete picture as the authors have themselves noted that those who smoke regularly tend to have a lower risk of obesity.

Only further research and investigation into the transgenerational effects of ancestral exposure can throw more light.

For now, there are many unanswered questions, including the linkages between effects of the habits of a person’s paternal side of the ancestors. Another question is why a similar outcome was not seen in the male offspring.

If these observations hold up in other cohorts of participants, perhaps the ubiquitous advisory “Smoking is injurious to health” will be inadequate—a possible addendum that can follow is: “Smoking is also injurious to your offspring’s health”.

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Findings of other smoking-related studies under the project

A study from 2013 showed that children as young as seven years old had elevated levels of cotinine—which is a by-product of nicotine—in their blood if their mother smoked. This was seen particularly in those children whose mothers smoked 10 cigarettes a day.

One study from 2014 shows that men who started smoking before the age of 11 had sons who on an average had about 5-10 kg more body fat than their peers.

A 2017 study showed that if a woman’s maternal grandmother smoked during pregnancy, she was 67 per cent more likely to display certain traits linked to autism, such as poor social communication skills and repetitive behaviours.

A study from May 2021 had a more obvious result associating smoking during pregnancy to a child’s risk of developing congenital heart disease.