When studies first suggested that alcohol, in moderation, may improve health, many of us were delighted at the news. But a new, in-depth review of these studies suggests that believing the health benefits of alcohol may be wishful thinking.

Previous research has indicated that a moderate amount of alcohol can protect against heart disease.

More than 100 prospective studies have shown an inverse correlation between moderate alcohol intake - defined as no more than one daily drink for women, and no more than two drinks per day for men - and the risk of heart attack, blood clots, stroke, and other adverse cardiovascular events.

Some researchers suggest that the connection is not just observational, but that it can also be backed up scientifically and biologically. Moderate amounts of ethanol seem to raise levels of the "good" kind of cholesterol, which has, in turn, been linked to a lower risk of heart disease.

But a new research review contests these findings. The extensive meta-analysis of existing studies was published in the Journal of Studies on Alcohol and Drugs.

The new review examined 45 cohort studies that showed people who drink moderately to be in better health than those who abstain from alcohol, therefore inferring that a moderate intake of alcohol may have positive health effects.

'Non-drinkers' may have stopped drinking because of poor health

Although the review confirmed that overall, those who drank moderately at the time they were included in the studies did have a lower risk of heart disease mortality, the results changed when the meta-review looked at people's drinking habits at a younger age.

Studies of participants aged 55 or younger who were clinically followed into older age found no correlation with alcohol. Additionally, studies that evaluated participants' heart health at baseline showed no benefits from alcohol.

The researchers point to a major misconception that may have misled the results of these studies: older "non-drinkers" included in the studies were, in fact, former drinkers who quit because of poor health.

In other words, rather than abstaining leading to poorer health, non-drinkers may have chosen to abstain because their health was already poor.

By contrast, "healthy" seniors who enjoy a glass of wine with dinner, the review suggests, are not healthy because they drink, but rather older people who are already in good health are simply more likely to enjoy a glass of wine with dinner because they have no reason not to.

Study researcher Tim Stockwell, Ph.D., director of the Centre for Addictions Research at the University of Victoria in British Columbia, Canada, explains further:

"We know that people generally cut down on drinking as they age, especially if they have health problems. People who continue to be moderate drinkers later in life are healthier. They're not sick, or taking medications that can interact with alcohol."

Another study reviewed by the analysis monitored more than 9,100 adults in the United Kingdom between the ages of 23 and 55 and found very few lifelong alcohol abstainers, thus supporting the idea that non-drinkers had, in fact, chosen to stop drinking because they already were in poor health.

An additional factor that the review brought to light is education. Non-drinkers were found to be less educated overall - and education is known to correlate with a longer lifespan and better health.

Stockwell notes, however, that their review does not prove causality and does not intend to dissuade moderate drinkers from drinking.

"We can't 'prove' it one way or the other. But we can say there are grounds for a healthy skepticism around the idea that moderate drinking is good for you [...] The risks of low-level drinking are small, [but] the notion that one or two drinks a day is doing us good may just be wishful thinking."