Friday October 26 2012
Even so-called social drinking can lead to health problems
“Just two glasses of wine a day could be harmful to the brain”, the Daily Mail warns, while the Daily Express, reporting on the same study, advises “even a small tipple everyday can have a huge impact, decreasing the production of adult brain cells by a massive 40%”.
The sobering headlines are based on a study that examined the effect of alcohol on the production of brain cells in rats.
The researchers found that rats exposed to moderate levels of alcohol each day produced 40% fewer new brain cells in a region of the brain associated with memory, compared to the teetotal group of rats. However, the drinking and non-drinking groups showed no differences in terms of motor functioning or learning ability.
It is also unclear whether the observed reduction in brain cell production has long-term effects.
Therefore, it should not be assumed that these results translate into longer-term brain damage and memory loss in humans.
Still, the research does highlight the fact that even moderate levels of drinking, if you drink on a daily basis, can be potentially harmful. It is recommended that you have at least one or two ‘booze free’ days each week.
Where did the story come from?
The study was carried out by researchers from Rutgers University in the US and the University of Jyvaskyla in Finland. The researchers were funded by the US National Institutes of Health and the National Science Foundation.
The study was published in the peer-reviewed journal Neuroscience.
The results and implications of this study were exaggerated in the media. The Daily Mail headline claimed that “two glasses of wine a day can nearly HALVE the number of brain cells we produce” and that “long term effects included impaired memory”.
In fact, this study did not examine:
- the entire brain
- the impact of drinking on memory
- the long term effects on cognitive function
Also, both papers could have made it clearer from the start that the study involved rats. The Mail does not do so until the sixth paragraph, while the Express waits until the tenth to provide this key piece of information.
An arguably more accurate, if less sensational headline, would have been ‘Daily alcohol consumption decreased brain cell volume in rats – long-term effects remain unknown’.
What kind of research was this?
This was an animal study that investigated how drinking alcohol everyday impacts the development of new brain cells, motor skill learning, and associative learning in adult rats. To do this, the researchers examined an area of the brain common to all mammals, called the hippocampus, which is thought to play a key role in memory formation.
A specific portion of the hippocampus, called the dentate gyrus, is known to produce new brain cells in adult rats, and studies suggest that humans also generate new brain cells in this region. This is the small area of the brain that the researchers examined.
Researchers often create animal models of human behaviours in order to glean information and form hypotheses on how an experimental situation would impact people.
In this study, the researchers attempted to model moderate human drinking (resulting in a blood alcohol concentration (BAC) of 0.08%, similar to the legal drink-driving limit in the UK) using adult rats. Such models can only attempt to approximate the target behaviour, and their results should not be generalised to people without the support of further studies in humans.
What did the research involve?
The researchers took two groups of rats, one that drank alcohol everyday, and the other that drank no alcohol. The rats were put on a liquid-only diet and were allowed to consume as much, or as little, of the liquid as they wanted. The researchers left a bottle of a mixture containing alcohol, water and a powdered diet in the cages of the exposed animals, and a bottle of water, maltodextrin (an additive) and a powdered diet for the non-exposed group. Thus, the alcohol group had exposure to alcohol every time they drank throughout the day for two weeks. The researchers assessed blood alcohol concentration (BAC) at one point in time: at the end of the two-week exposure period, three hours after the end of the rats’ active time of day.
To assess the impact of continuous alcohol exposure on brain cell production, the researchers examined the brains of 37 rats after two weeks of this liquid diet, and compared the number of new brain cells produced in the dentate gyrus in the alcohol-exposed rats versus the teetotal rats.
To assess the effect of moderate drinking on motor function, the researchers conducted a test known as a rotarod test. A rotarod test involves placing the animal on a rod that rotates eight times per minute for up to five minutes, and then measuring the amount of time it takes the animal to fall off the rod.
In total, 12 female rats (half from the drinking group and half from the non-drinking group) were tested on the sixth day of alcohol exposure. The researchers conducted three rounds of this experiment (with 20 minutes between each round).
To assess the impact of alcohol on associative learning (the ability to learn from experience, such as avoiding pressing a button that then gives you an electric shock), the researchers also carried out a test called trace eyeblink conditioning. During this test, the animal learns over multiple trials to blink in response to a stimulus. The researchers compared the number of conditioned responses (blinks) between the two groups.
The study authors used statistical methods to analyse differences between the alcohol-exposed and non-exposed groups.
What were the basic results?
The researchers found that the alcohol-exposed rats had an average BAC of 0.0864% for males and 0.0876% for females, similar to the 0.08% legal drink-driving limit in the UK. The range of BAC across the animals, however, was from 0.052% to 0.1476% (meaning that some rats were bigger drinkers than others).
The researchers found that rats in the alcohol group produced significantly fewer new cells in the dentate gyrus compared to the non-alcohol-exposed rats.
When assessing the impact of alcohol on motor functioning (in the middle of the two-week consumption period), the researchers report that statistical tests resulted in no significant difference between alcohol-exposed and non-exposed female rats in the time taken to fall off the rotating rod (p-value >0.05). However, examining the published figure associated with this experiment indicates that alcohol-exposed rats may have actually taken longer to fall of the rod in the second and third trial.
Finally, when examining the effect of two weeks of continuous drinking on associative learning (two days after the end of the bender), the researchers found no difference in learning ability between the two groups of mice.
How did the researchers interpret the results?
The researchers concluded that “even socially acceptable levels of alcohol consumption can have long-lasting and detrimental consequences for brain health and its structural integrity”.
This study suggests that rats that continuously drink alcohol at a ‘moderate’ level, produce fewer new cells in a specific region of the brain called the dentate gyrus, but in the short-term, this drinking has no significant impact on motor function or associative learning. Whether these results hold in the long-term for rats, or at all in humans, is unknown based on this study.
The researchers report that rats are most active at night, and that it is presumed that they drank the most at night, thus the peak BAC may have been higher than those detected during the day. They say that similar studies found a peak BAC in rats of approximately 0.145% at night, and 0.085% during the day. Thus, it is unclear if this model represents moderate alcohol consumption. The authors also say that “lower levels of alcohol more consistent with one to two drinks a day may not produce a deficit, or alternatively, may produce less of a deficit” in terms of new brain cell development.
As noted by the study’s author “it is not clear whether moderate drinking is beneficial or harmful to overall brain health and function”. Studies with seemingly conflicting results are published on a regular basis. This study adds to the literature on the impact of alcohol on the brain, but given that it was conducted in rats, and did not include any long term follow up, it is not sufficient on its own to sound alarm bells that moderate drinking ‘can cause brain damage’.
While the authors suggest that this behaviour may reflect a similar pattern of behaviour in humans who drink a few drinks every day during the working week and more on the weekends or holidays, this is certainly open to debate. The rats used in this study were on a liquid-only diet, and were exposed to alcohol every time they took a drink of water. While this was intended to reflect human moderate alcohol consumption, it is unlikely that many moderate drinkers consume as continuously as the rats in this study.
While the results of this study should only be generalised to humans with great caution, it is probably advisable to avoid a pint with your Weetabix in the mornings, and you should spend some days of the week not drinking at all.
For more information on current recommendations for safe drinking, including what constitutes a unit of alcohol, see Live Well: drinking and alcohol.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on twitter.