Tuesday March 10 2009
Rats exposed to alcohol in the womb grew to like its taste and smell more
Drinking during pregnancy could make your child “develop a taste for booze before birth”, reports The Sun. The newspaper suggests the practice could increase the risk of heavy teenage drinking.
This news is based on a study which found that rats that were exposed to alcohol in the womb “were more likely to ‘sniff out’ drink during adolescence”. Researchers suggest that this may be because alcohol may “taste and smell better” to those who experience it before birth. As this study was conducted in rats, it may not reflect what would happen in humans. However, regardless of whether or not drinking during pregnancy influences a child’s future alcohol consumption, it is clear that excessive drinking during pregnancy can harm both babies and mothers.
Current guidelines from the National Institute for Health and Clinical Excellence (NICE) advise that women who are pregnant or planning a pregnancy should avoid alcohol in the first three months of pregnancy as it may be associated with an increased risk of miscarriage. If women choose to drink during pregnancy, NICE advises them not to exceed one to two units once or twice per week, and to avoid getting drunk or binge drinking.
Where did the story come from?
Drs Steven L. Youngentob and John I. Glendinning from the State University of New York Upstate Medical University and Columbia University carried out this research. The study was funded by the National Institutes of Health in the US, and published in the peer-reviewed scientific journal Proceedings of the National Academy of Sciences USA.
What kind of scientific study was this?
This was an animal study looking at how foetal alcohol exposure in rats influences their preference for alcohol by affecting its perceived taste and smell.
The researchers took pregnant rats and randomly assigned them to one of three diets. One liquid diet included alcohol (35% of calorie intake from alcohol); the second liquid diet contained no alcohol but a similar calorie intake; the third diet consisted of normal rat food (chow) from the fifth day of pregnancy. The last two groups were controls.
In their first experiment, the researchers looked at whether this foetal exposure affected the taste of alcohol in offspring at 30 days of age (adolescence) or at 90 days (adulthood), and whether it achieved this by reducing its bitterness or increasing its sweetness.
To do this, they randomly selected 12 offspring (six male, six female) from each group. They gave the offspring rats different concentrations of alcohol (ethanol), another bitter-tasting substance (quinine) or sugar (sucrose), using a special “taste testing” machine. This machine recorded how often the rats licked the source of each substance during three 30-minute tests on separate days.
In each test, water was also included as an alternative drink. Each substance was tested on a separate day, with a recovery day between each test. The number of licks of the test substance was divided by the number of licks of water to standardise for differences between the individual rats.
In the second experiment, the researchers exposed twenty randomly selected 15-day-old offspring from each of the three groups to test their liking for the smell of alcohol. They placed the mice in a chamber that measured their breathing, and introduced either just air, or air containing varying amounts of ethanol odour.
The researchers then compared the characteristics of the rats’ breathing, and produced a “sniffing index”, which they used to compare the three groups. They then fed an alcohol-infused solution into these rats’ mouths and measured how much of it they swallowed.
What were the results of the study?
In the taste test, the researchers found that adolescent rats that had been exposed to alcohol in the womb liked alcohol and quinine more than the control rats, i.e. they licked these sources more. The groups did not differ in their liking for a sugar solution.
Statistical tests suggested that a reduced dislike for bitterness accounted for around 29% of the effect that foetal alcohol exposure had on fondness for alcohol in adolescence. However, once the foetal rats reached adulthood, there was no significant difference between the alcohol exposed and unexposed groups in their liking for alcohol, quinine or sugar.
At 15 days of age, rats exposed to alcohol in the womb showed a reduced sniffing response to alcohol odour compared with control rats. They also swallowed more alcohol than control rats. Statistical tests suggested that a reduced dislike for the smell of alcohol accounted for about 22% of the effect of foetal alcohol exposure on alcohol consumption.
What interpretations did the researchers draw from these results?
The researchers concluded that foetal alcohol exposure increases the rats’ liking for alcohol, in part by making it taste and smell better. They suggest that these mechanisms may also play a role in transferring the mother's consumption of other substances, such as tobacco or marijuana.
What does the NHS Knowledge Service make of this study?
This study was carried out in rats and may not reflect what would happen in humans. Whether a person drinks alcohol and how much of it they drink is likely to be affected by a number of varying influences.
Regardless of whether drinking during pregnancy alcohol affects a child’s future preference for alcohol, it is clear that excessive consumption of alcohol during pregnancy can be harmful to the baby and mother.
Recent guidelines from the National Institute for Health and Clinical Excellence (NICE) advise that pregnant women and women planning a pregnancy should avoid drinking alcohol in the first three months of pregnancy, as it may be associated with an increased risk of miscarriage.
If women choose to drink alcohol during pregnancy, NICE advises that they should drink no more than one to two UK units once or twice a week, and should avoid getting drunk or binge drinking (defined as more than five standard drinks or 7.5 UK units on a single occasion).