Drinking just one alcoholic beverage a week during pregnancy can reduce a child’s IQ by almost eight points by the age of eight, a major study revealed yesterday.
Research found that mothers who consume less than one to six units of alcohol a week can affect the development of their baby’s brain in the womb.
One standard glass of wine, which is 175ml, contains around 2.1 units – more than double the amount found to affect IQ in the study.
Current NHS Guidelines advise women to drink “no more than one to two units of alcohol once or twice a week”.
Scientists from the University of Bristol and Oxford University quizzed 4,000 mothers about their drinking habits when they were 18 weeks pregnant.
They found that the mother’s alcohol consumption during pregnancy caused up to four differences in the genes of their children.
Each of these genetic changes led to an average drop in IQ of nearly two points by the age of eight.
Children whose mothers completely abstained from alcohol did not experience any modifications. Heavy drinkers were not included in the study.
Dr Sarah Lewis, main author of the findings which were published in the journal PLOS ONE, said even small amounts of alcohol affected brain development.
She said: “Our results suggest that even at levels of alcohol consumption which are normally considered to be harmless, we can detect differences in childhood IQ, which are dependent on the ability of the foetus to clear this alcohol.
“This is evidence that even at these moderate levels, alcohol is influencing foetal brain development.”
The data of 4,167 children and their mothers was taken from the Children of the 90s Study, carried out by Bristol University.
Scientists in the study – believed to be the first substantial one of its kind – used genetic variation to investigate the effects of drinking less than one to six units of alcohol per week.
Previous research has been “conflicting” on whether drinking in pregnancy is safe and official guidelines vary.
This is because it is difficult to separate the effects of moderate alcohol consumption from other lifestyle and social factors such as diet, smoking and affluence.
Some studies have even suggested that moderate drinking is beneficial compared to abstention.
But this is because mothers who only drink a little are likely to be well educated, with a good diet and non-smokers – all factors linked to a higher IQ in children.
Results from the latest study are not affected by these factors – as individual variations in DNA are not connected to lifestyle and social factors.
Dr Ron Gray from the University of Oxford, who led the research, added: “This is a complex study but the message is simple: even moderate amounts of alcohol during pregnancy can have an effect on future child intelligence.
“So women have good reason to choose to avoid alcohol when pregnant.”
When a person drinks alcohol, ethanol is converted to acetaldehyde by a group of enzymes.
Variations in the genes that ‘encode’ the enzymes lead to differences in their ability to metabolise ethanol – with peak alcohol levels remaining higher and lasting longer in ‘slow metabolisers’ than ‘fast metabolisers’.
It is believed that ‘fast’ metabolism of ethanol protects against abnormal brain development in babies because less alcohol is delivered to the foetus.
Alcohol – like carbon monoxide from cigarettes – passes easily through the placenta from the mother’s bloodstream into her baby’s blood.
The blood alcohol level of the foetus becomes equal or greater than the blood alcohol level of the mother and remains high for a long period of time.
This is because a foetus cannot break down alcohol in the way an adult can.
In the study, the mothers’ alcohol intake was based on a questionnaire completed when they were 18 weeks pregnant.
They completed another questionnaire at 32 weeks gestation which asked about average weekday and weekend alcohol consumption, from which weekly intake was worked out.
Women who reported drinking – even if it was less than one unit per week – were classed as drinking during pregnancy.
Any women who reported drinking two pints of beer – of the equivalent number of units – on at least one occasion was classed as a binge drinker and excluded from the study.
The children’s IQ was tested when they were aged eight using a shortened version of the Wechsler Intelligence Scale for Children.
An overall age adjusted total score was derived from their result.
Foetal alcohol exposure and IQ at age 8: evidence from a population based birth-cohort study was published in PLOS ONE yesterday.