Knocking back a glass of wine each day has long been linked to good health. That is, of course, as long as it's one glass and not the entire bottle.

Wine protects against diseases of the heart and the brain, including coronary artery disease, stroke, Alzheimer's disease and other forms of dementia. Wine drinkers even have lower rates of certain cancers compared to folks who don't partake. In general, those who drink wine live longer than those who drink beer or other kinds of booze.

Yet scientists have wondered: is wine really such a powerful elixir? Red wine contains antioxidants that have powerful health-protecting properties, but the relationship may not be simple cause and effect. Perhaps wine drinkers also take better care of themselves—they may also eat more healthfully and exercise more regularly than beer drinkers or teetotalers. In other words, perhaps wine is a marker for a certain lifestyle?

A study suggests the benefits of wine are at least in part due to the smart dietary choices of wine connoisseurs. Danish researchers analyzed 3.5 million supermarket receipts and found that wine drinkers (people who bought wine as their only form of alcohol) tended to buy more fruits, vegetables, low-fat meats and cheeses than do other shoppers.

Beer drinkers, on the other hand, filled their carts with ready-to-eat dishes, cold cuts, sausages, sugary items and soft drinks, the researchers report online in the British Medical Journal.

These divergent shopping lists suggest that lifestyle choices may be more important than the type of alcohol a person drinks when it comes to determining mortality risk.

Other demographic patterns emerged among the Danish wine drinkers that could also influence their lower mortality rates. They tend to be more highly educated, wealthier and in better physical shape than beer drinkers. Similar results have been found in a Californian population, suggesting this isn't just a quirk of the Danish study.

It seems that no matter where they live, wine drinkers tend to subscribe to the so-called Mediterranean diet—chock full of fresh produce and healthy, unsaturated fats like those in olive oil and fish, with a minimum of artery-clogging fat from meats and processed foods.

Another wrinkle: scientists note that wine usually accompanies a meal, which means that the alcohol may be better tolerated by the body. In contrast, beer or other spirits tend to be enjoyed on a fairly empty stomach—say, while watching the game on TV or sidled up to a bar.

Still, even with all the evidence that wine may not be a cure-all, let's not discount the power of a glass of Chilean Shiraz.

Scientists have identified some 6,000 antioxidants in wine, especially wines made with grape skins, which turn the wines red in color. In general, foods that have dark pigments—such as blueberries, cherries, spinach or kale—are also packed with cell-protecting chemicals.

These antioxidants do their work by disarming rogue molecules known as free radicals, which damage cell membranes and oxidize "bad" cholesterol, leading to hardened arteries.

A daily tipple of alcohol—any alcohol—also thins the blood and prevents blood clots.

So go ahead, uncork that bottle. Just put down that wurst.