Over the decades, study after study showed how much heavy alcohol drinking is bad for your health – liver disease, of course, heart and kidney disease, mental deterioration, and even cancer.
Certainly, the warnings about alcohol intake and pregnancy, sometimes resulting in fetal alcohol syndrome, were obvious enough on general observation. What is not obvious, until a study by Bristol and Oxford universities (U.K.) of 4,000 mothers and their children, is that relatively small levels of exposure to alcohol while in the womb can harmfully influence a child’s IQ.
Published in November in the online journal PLoS One, the new study takes to task the common advice given to pregnant women that moderate alcohol consumption is not harmful to the fetus. At best, the guidelines are contradictory – some countries saying that all alcohol consumption should be ended during pregnancy (total abstinence) and others saying that some drinking is safe.
According to the new study, it is not safe. This is the first study to use genetic variation to investigate the effects of moderate alcohol consumption (1-6 units of alcohol per week) during pregnancy. By comparing women based on their genetic variations, rather than on their lifestyle and social factors, the study simplifies the comparison.
The researchers identified four genetic variants in alcohol-metabolizing genes among 4,167 children in the study, each strongly related to lower IQ by age eight. The child’s IQ was, on average, almost two points lower per each genetic modification they possessed. This effect appeared only in children whose mothers were moderate drinkers and not at all in children whose mothers abstained from drinking. (Heavy drinkers were not included in the study.)
At the heart of the study was the use of Mendelian randomization, where the women in the study were categorized by their gene variations rather than by age, lifestyle or other factors. This bypassed the problem encountered in other studies where the women most likely to observe moderation or abstinence in drinking while pregnant were also women who were well-educated, had a good diet, were unlikely to smoke andhade some training in nativity – that is, women whose factors might mask the effect of alcohol.
In this study, these observational conditions did not matter. The researchers considered relevant only the women’s genetic variations on the four key genes. The genes’ role is to produce the enzymes that convert alcohol (ethanol) into acetaldehyde, which is not as toxic as ethanol. Variations in these genes account for why some people are ‘fast metabolizers,’ converting alcohol to acetaldehyde very quickly or ‘slow metabolizers.’ With slow metabolizers, the alcohol level of the blood remains high for a longer time, which means it has a greater probability of reaching the blood flow to the fetus.
The mothers in the study filled-out a questionnaire when they were 18 weeks pregnant, detailing their alcohol consumption before and during pregnancy. They completed another questionnaire after 32 weeks of gestation. The children’s IQ was tested when they were eight years old using a shortened version of the Wechsler Intelligence Scale for Children.
The researchers found that even drinking roughly one beer a week (or its equivalent) was enough to affect a child’s IQ by a measurable amount. It could be said that a few percentage points of IQ – even assuming the accuracy of the IQ test – is hardly enough to condemn all alcohol consumption. But the point of the study was that even minor amounts of alcohol were potentially harmful and that binge drinking or even a week or two of more than average drinking could seriously affect a child’s IQ.
Of course, a key piece of the study was the identification of children whose genes for blood alcohol conversion are deficient. Whether this was a parental inheritance or another effect of the alcohol was not determined. Nevertheless, the researchers concluded their study with the advice that even moderate drinking of alcohol while pregnant is a risk for lowering the IQ of the child. It’s not a good risk, at any level of cause and effect.
