Mothers who smoke while pregnant might be causing changes in their unborn babies that can lead them to have lower amounts of high density lipoprotein (HDL) cholesterol, scientists said.
In a study reported in the European Heart Journal, Australian researchers found that by the age of eight, children born to mothers who smoked in pregnancy had HDL cholesterol levels of around 1.3 mmol/L, compared to about 1.5 mmol/L in children whose mothers who hadn't smoked.
"Our results suggest that maternal smoking 'imprints' an unhealthy set of characteristics on children while they are developing in the womb, which may well predispose them to later heart attack and stroke," said David Celermajer at the University of Sydney.
"This imprinting seems to last for at least eight years and probably a lot longer," he said, adding that the heart disease risk for smokers' children could be 10% to 15% higher.
Smoking during and after pregnancy is already known to be linked to a wide range of childhood health problems, including behavioural and cognitive problems and sudden infant death.
Prevalence still high
Yet the prevalence of smoking while pregnant is still high, at around 15% in many Western countries, the researchers said. And until now scientists were not sure how prenatal exposure to cigarette smoke might affect future heart risks.
Celermajer's team analysed data from 405 healthy eight year olds, born between 1997 and 1999, who had been enrolled before birth into a randomised controlled trial that was investigating asthma and allergic diseases.
The researchers collected data before and after the children were born, including information on mothers' smoking habits before and after pregnancy, exposure to passive smoke, and data on height, weight, waist measurement and blood pressure.
They used ultrasound scans to measure the arterial wall thickness and, in 328 children who agreed, they took blood to measure lipoprotein levels.
Although there was no effect on the thickness of the children's arterial walls, Celermajer's team found there was an association with levels of HDL cholesterol.
He suggested that lower HDL levels at this age might have a serious health impact in later life, since the children will probably continue to have low levels as they grow up.
"Cholesterol levels tend to track from childhood to adulthood, and studies have shown that for every 0.025 mmol/L increase in HDL levels, there is an approximately 2% to 3% reduction in the risk of coronary heart disease," he said in a statement about his research.
"If we extrapolate this, we can suggest that the difference between children of smoking mothers versus non-smoking mothers might result in a 10% to 15% higher risk."
(Reuters Health, Kate Kelland, June 2011)