Introduction

Those who like their daily drink (or two, or three) have received further encouragement from a recent report in Lancet. The investigators analyzing data from the Rotterdam study have examined the effect of drinking alcohol on the likelihood of developing dementias, such as Alzheimer's disease. Here's a summary of their findings.

How the study was done

Everyone over 55 living in a suburb of Rotterdam, Netherlands, between 1990 and 1993 were invited to take part. Out of 8,000 who accepted, over 7,000 that were free of dementia (but therefore at risk of developing it) were enrolled. They completed questionnaires about their eating and drinking habits at the start of the study period, which ran for an average of 6 years.

They were asked if they ever drank alcohol, and if so, how often. Those that took at least two drinks a month were asked to give a breakdown of the average amounts of different drinks they had - wine, beer, liquor, or fortified wine. There were questions on changes in the pattern of alcohol intake, as well as on binge drinking (more than 6 drinks on one day).

Based on their drinking habits, participants were assigned to one of 5 classes: non-drinkers, less than one drink a week, between one a week and one a day, one to three drinks a day, and more than 4 a day.

Participants were followed by their family practitioners, and attended at intervals during the study, which ran until December 1999. They underwent screening tests for dementia. First, simple tests of thinking processes and memory screening were done, and then, if any problems were detected, full testing for dementia, including an interview with a family member or close friend. Finally, those with suspected dementia were examined by a neurologist and had neuropsychological tests. The type of dementia -- Alzheimer's or vascular dementia -- was determined.

What was found

During the 6-year follow-up period, 197 people developed dementia. Alzheimer's disease was diagnosed in 146, vascular dementia in 29, and another type (e.g. a complication of Parkinson's disease) in 22.

On average, this group of people took about 1 drink every 3½ days. Men drank more than women, consuming chiefly beer and liquor; women drank more fortified wine (e.g. sherry).

Those people who took 1-3 drinks a day were found to have a significantly reduced risk of developing any sort of dementia -- in fact, they had about a 60% chance, compared with non-drinkers. When it came to different types of dementia, those taking 1-3 drinks a day had roughly a 70% chance of developing Alzheimer's, and only a 30% chance of developing vascular dementia, compared with non-drinkers.

These effects were more obvious in men; the chances for any dementia in men taking 1-3 drinks a day being 40%, compared with 80% in women.

There was an important additional finding; taking 4 or more drinks a day seemed to have a 'negative' effect. In other words, these participants had a slight, though not significant, increased likelihood of developing vascular dementia, or, to a lesser degree, Alzheimer's. Clearly, the 'dose' is very important.

Interestingly, there were no real differences in the risk of dementias according to the type of alcoholic drink consumed.

What does it mean?

This is not the first report of a beneficial effect of alcohol on the chances of developing dementia. An earlier study showed that drinking wine decreased the likelihood of dementia in a sample of citizens of Bordeaux¹. This time, there was no evidence that any one type of beverage was superior in it's effect.

The authors of the study suggest two possible explanations for their findings. First, alcohol might act by lowering cardiovascular risk factors, either by hindering platelets from clumping together, or by lowering serum cholesterol and triglycerides. The fact that vascular dementias were benefited more than Alzheimer's fits with this theory.

Second, alcohol might have a direct action on thought processes by releasing acetylcholine in a particular part of the brain, the hippocampus. In lab animals, low alcohol concentrations stimulate, while high concentrations inhibit, acetylcholine release in the brain.

Although these results suggest strongly that mild-to-moderate alcohol drinking helps prevent dementias (especially vascular dementia), they should not be taken as a reason for non-drinkers to start drinking, or for infrequent drinkers to increase their consumption. However, the findings should remove any guilt that moderate drinkers may feel as they enjoy their daily glass (or two). And, they clearly emphasize that any possible benefits are clearly lost if the drinker exceeds 4-a-day. Once again, "moderation in all things".