Read on for the truth behind the health benefits of that glass of wine.

The theory that moderate drinking can be beneficial to your health is good news for many. Unfortunately, it's not as simple as, A glass of wine a day keeps the doctor away.

While it has been shown that small amounts of alcohol protect against heart disease, people should take other factors into consideration before they tip their glasses, according to Samir Zakhari, director of the division of metabolism and health effects at the U.S.-based National Institute on Alcohol Abuse and Alcoholism (NIAAA).

The NIAAA conducted a review that weighed the risks of alcohol consumption against the benefits of moderate drinking; namely a reduced risk of heart disease. According to Zakhari, alcohol's protection against heart disease is relatively small, and is even smaller for those under the age of 40. Zakhari also warns that there are drawbacks to moderate drinking; for example, alcohol has calories, and drinking over long periods of time can lead to liver disease as well as tissue damage, including fatty liver or fibrosis. For people who have a family history of alcoholism, moderate drinking can easily lead to heavy drinking, and moderate drinking is also unsafe for pregnant women.

"The degree of potential benefit from moderate drinking varies among people based on their susceptibility, genetic makeup, lifestyle and so on, so we cannot make a blank statement saying that alcohol is good for the heart or that alcohol is bad for the liver," Zakhari says. The amount of alcohol the NIAAA deems "moderate" is also elusive and, depending on age, weight and gender, varies from a few drinks a day to two drinks a week.