Even relatively small levels of exposure to alcohol while in the womb can adversely affect a child’s IQ, according to a new study.
Researchers from the universities of Bristol and Oxford in England, using data from more than 4,000 mothers and their children in the Children of the 90s study (ALSPAC), analyzed genetic variations to investigate the effects of moderate drinking — defined as six or less alcoholic drinks a week — during pregnancy.
They discovered that four genetic variants in alcohol-metabolizing genes among the 4,167 children were strongly related to lower IQ at age 8. The child’s IQ was on average almost two points lower per genetic modification they possessed, according to the study.
The researchers note that this effect was only seen in the children of women who were moderate drinkers. There was no effect evident among children whose mothers did not drink during pregnancy, suggesting that it was the exposure to alcohol in the womb that was leading to the difference in IQ, according to the researchers. Heavy drinkers were not included in the study.
When a person drinks alcohol, ethanol is converted to acetaldehyde by a group of enzymes. Variations in the genes that “encode” these enzymes lead to differences in the ability to metabolize ethanol, the researchers explained. In people who are slow metabolizers, peak alcohol levels may be higher and persist for longer than in those who are fast metabolizers.
The researchers note that it is believed that the fast metabolism of ethanol protects against abnormal brain development in infants because less alcohol is delivered to the fetus, although they note that the exact mechanisms are still unclear.
Previous studies relied on observational evidence, but this is problematic, according to the researchers. Observational studies often find that moderate drinking is beneficial compared to abstention, but this is because mothers who drink in moderation during pregnancy are typically well-educated, have a good diet and are unlikely to smoke — all factors linked to higher IQ in the child, and which mask any negative effect that exposure to alcohol may have, the researchers explain.
This study, on the other hand, used a technique known as Mendelian randomization, which is “a scientifically robust way” of investigating the links between exposures and later diseases, using genetic variants that modify exposure levels and are not influenced by lifestyle or other factors, the researchers said.
The mothers’ alcohol intake was based on a questionnaire completed when they were 18 weeks pregnant. It included questions about the average amount and frequency of alcohol consumption before the current pregnancy, during the first trimester, and in the previous two weeks or at the time when they first felt the baby move.
Around 32 weeks the mother completed another questionnaire in which she was asked about her average weekday and weekend alcohol consumption, from which weekly intake was derived. Any woman who reported drinking, even if it was less than one drink per week either in the first trimester or when she felt the baby first move, was classified as drinking during pregnancy.
The children’s IQs were tested when they were 8 using a shortened version of the Wechsler Intelligence Scale for Children from which an overall age adjusted total score was derived.
“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 fetus to clear this alcohol,” said Sarah Lewis, Ph.D., the study’s main author. “This is evidence that even at these moderate levels, alcohol is influencing fetal brain development.”
Dr. Ron Gray from the University of Oxford, who led the research, noted that while the study was complex, its message was 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,” he said.
The study was published in PLOS ONE.
Source: University of Bristol