Smoking in pregnancy damages an unborn baby’s DNA – increasing its risk of a premature death, according to new research.
It alters chemicals that turn genes on or off – making the infant prone to illnesses seen in adult smokers.
Known as ‘epigenetic tags’ these changes can lead to obesity, cardiovascular disease, diabetes and cancer.
It should serve as a warning for women smokers – more than half of whom continue during pregnancy, say scientists.
Study leader Professor Marjo-Riitta Jarvelin, of Imperial College London’s School of Public Health, said: “Our study shows compelling evidence that changes in epigenetic markers may persist over the lifetime of an individual.”
It was based on data from more than 18,000 people across the world – including the UK, US and Australia.
The findings published in EBioMedicine show for the first time how smoking during pregnancy harms the baby’s DNA in the womb without changing the genetic ‘code’ itself.
Instead, it adds or removes the exterior epigenetic chemicals that regulate genes “like chemical sticky notes,” said the researchers.
The process, called DNA methylation, adjust how certain regions of DNA are read and copied – affecting the activity of key genes.
These changes are found in people whose mothers smoked while they were in the womb – and in current smokers.
They are strongly linked to smoking-related diseases – including adult obesity, said the researchers.
Smoking during pregnancy can lead to premature birth and low birth weight, as well as predisposing the child to higher risk of heart disease and diabetes in later life,
But the exact mechanisms underlying these longer-term effects were unclear.
Yet despite the danger, an estimated 53 per cent of women who smoke daily continue during pregnancy.
Added Prof Jarvelin added: “These findings are important for health policy makers to further draw attention towards increasing awareness on smoking cessation programmes and for better prevention strategies in maternity clinics and health centres.”
Her team focused on methylation of a gene called GFI1, known to be linked with smoking.
Using data from 22 population-based studies from Europe, the US and Australia, the they looked at the link between maternal smoking and epigenetic changes in a number of regions of the gene.
They identified lower DNA methylation of GFI1 in those who smoked or whose mother smoked while they were pregnant.
These changes are associated with increased BMI (body mass index) and higher levels of blood pressure and blood lipids in adulthood.
This means exposure to cigarette smoking in the womb ultimately increases a person’s risk for a range of health conditions in adulthood including diabetes, heart disease and stroke.
Co author Priyanka Parmar, from the University of Oulu, Finland, said: “Such epigenetic loci might serve as objective biomarkers of past environmental exposures that could be used for preventive health measures.
“This discovery provides a strong foundation for further work to unravel emerging smoking epigenetic markers with downstream detrimental health outcomes.”
Cigarette smoking accounts for an estimated six million deaths each year and even former smokers are at long-term risk of cardiovascular diseases, lung cancer and stroke.
The work highlights an underlying epigenetic component for maternal smoking exposure and disease risk. But the size of the effect is unclear.
The team now hopes to explore more genetic regions linked with maternal smoking exposure and disease risk, highlighting that their work focused on just six genetic markers out of a potential 6,000.
Previous research has shown smoking during pregnancy chemically alters the DNA of unborn babies that mirror patterns seen in adult tobacco users.
Scientists in the US analysed the DNA of more than 6,000 mothers across the world and found children of those who smoked while pregnant had DNA modified in ways that could affect the functioning of genes.
Nearly half of those genes play a role in lung and nervous system development, smoking-related cancers and birth defects – including cleft lip and palate.
By Ben Gelblum and Mark Waghorn