The results come from an observational study in which, every few years, researchers asked people to report their drinking habits. It went on for 30 years, and when it ended, the analysis provided some information about what influences how much a person's drinks.
If you think about what is contagious, you might think a cold. But there is also social contagion, and drinking habits fall in this category. Genetics or family history may influence how much or if you drink, but so does, the drinking habits of your friends.
"What your friend are doing, when it comes to drinking, can be as important, if perhaps not even more important, than those other kind of biological or clinical factors we're accustomed to thinking about," said Dr. Nicholas Christakis, of Harvard University.
Dr. Christakis examined data from the Framingham Heart study of more than 12,000 people for more than 30 years.
The analysis looked at patterns of alcohol use in large social networks to see if there were clusters of heavy drinkers or abstainers.
The findings included a stronger connection amongst immediate friends.
"If your friends drink, it increases the likelihood that you'll be a drinker by about 50 percent," Dr. Christakis said.
But the effect continues as the social networks extend outwards
"If your freinds' friends drink, it increases the likelihood that you'll be a drinker by about 36 percent," Dr. Christakis said. "And if your friends' friends' friends drink, it'll increase the likelihood that you'll be a drinker by about 15 percent."
The researchers say the study could have implications for alcohol treatment. It could also be important as a warning of overuse.
"If we try to get one person to stop drinking, what we really should be doing is attending to how groups of people around them, how they're drinking," Dr. Christakis said. "And how we might get them to stop drinking."
Also, it is important to note that when one person stops drinking heavily, he or she benefits many other people, even people in outer circle he or she doesn't even know. Knowing that a lot of people in your circle are drinking, or people in their circle whom you don't even know, you can recognize that you are at risk for heavier drinking. The study is published in the Annals of Internal Medicine.