Amid groups of friends, he looks for keys to health

"People are social animals," said Harvard researcher Nicholas Christakis, who believes doctors will better understand their patients when they view them as social beings. (PAT GREENHOUSE/GLOBE STAFF)

"Obesity can spread like a contagious disease," William Shatner's character says on the preview clip for tomorrow's episode of "Boston Legal."

"That's not my opinion," Shatner continues. "That's Harvard's."

For Nicholas Christakis, this is what it has come to. After an MD and a master's degree in public health from Harvard Medical School, a doctorate in sociology from the University of Pennsylvania, and a distinguished career as a physician, professor, and researcher, Christakis laughs to think that, at age 45, the first line of his obituary has already been written.

"Nicholas Christakis, a Harvard University professor who co-authored a study that said you can get fat from your friends . . . "

This is the sexy, heavily condensed, and mostly inaccurate way to look at his study; it is the favored view for the writers of blogs, catchy headlines, and Hollywood shows (on "Boston Legal," the study serves as the legal defense for firing someone for being obese).

What's often overlooked is that the study, which found clusters of obesity and statistical evidence that it appears to spread through social ties, is not primarily about obesity. It's about social networks, about how your friends and their friends and their friends can impact your health in a medical game of six degrees of separation.

"This study was about taking seriously the notion that people are social animals and bringing that into medicine," Christakis said last week at his Cambridge office. "No man is an island. What happens to me affects you, and so on and so on."

At its core, Christakis's work addresses the old question of whether those who share social behaviors become connected - the old "birds of a feather flock together" - or whether those who are connected start to share behaviors, which is the concern of parents who don't want their kids hanging out with the wrong crowd.

To explore that riddle, Christakis and his co-author, University of California-San Diego political science professor James Fowler, chose obesity as their first topic for publication solely because it had the best available data set, thanks to 32 years worth of detailed information on the body mass index and social network of over 12,000 participants in the Framingham Heart Study. It could have been the spread of happiness, smoking cessation, or the eating of bananas within social networks - they've also studied those - but they chose obesity, which just so happens to be a hot, and controversial, topic in the culture at the moment.

"Many people felt that we just added another stigma to obesity, so it's been interesting to watch how our work has been interpreted and misinterpreted," Christakis said of the flood of media coverage, which included front-page stories in major newspapers across the country and, according to Christakis's figures, a mention on 10,000 blogs. "It was a bit of a perfect storm, because we tapped into issues of contagion, issues of blame, and issues of appearance. Except we never used the words 'contagion' or 'blame,' and we never suggested you sever ties with your friends."

As he got up from the couch in his office to show off framed copies of front-page stories that ran in The New York Times, Chicago Tribune, and Washington Post, Christakis said he has been flattered by the response to his study. He's also quick to laugh at all the hubbub.

For the record, Christakis is not obese. A black belt in Shotokan karate, he is fit and boyishly good-looking beneath his salt-and-pepper hair. And, according to Fowler, he deserves credit for "thinking outside the box" in the medical sense.

"He's reintegrating all of these fields that have been spread apart over the years," Fowler said. "I'm constantly amazed at how he'll bring up something from an unrelated field, but it's relevant and new and original."

Christakis's current research in broader networks is really an extension of questions he began studying as a young hospice doctor on the South Side of Chicago. "I became interested in caregiver burden and how it affected the health of everybody else in the house," he said. "We were among the first to document that caregiving can be fatal."

Christakis thinks his research highlights the need to assess more than the patient when looking at medical care.

"Say you have an insurance company that's weighing the cost-effectiveness of treating a woman for post-partum depression," he says as an example. The patient will be healthier, yes, but Christakis argues that her health will then impact her social network. If she's healthy "she's more likely to vaccinate her children. To the list of benefits [of treating her for depression], we have to add the collateral effects to those all around her."

Being so tangled-up in cause-and-effect has influenced his life, Christakis said, and he's become much more mindful of how his own actions and emotions affect those around him.

"I see networks everywhere now. I can't not see them. And I see their impact everywhere. In my kids' school. In meetings. In mobs. On the floor of a hospital."

"I feel like the guy in 'The Matrix,' " he said of the film that presents a world that is a simulated, interconnected reality. In the film, the hero takes a pill that wipes away his blissful oblivion and reveals to him the secret of the Matrix.

"That's me," Christakis said. "I feel like Neo."

Hometown: Was born in the United States, but spent the first six years of his life in Greece. He grew up in Washington, D.C., and currently lives in Concord.

Education: Earned a bachelor's degree in biology from Yale University in 1984, an MD and a master's of public health from Harvard Medical School in 1989, and a PhD in sociology from the University of Pennsylvania in 1995.

Family: Wife, Erika, 44, is an anthropologist and elementary school teacher at the Lincoln Nursery School. They have three children, Sebastian, 15, Lysander, 12, and Eleni, 10.

Hobbies: Christakis says he's married to his work and doesn't have a television (so he won't be watching "Boston Legal") but still found time to earn a black belt in Shotokan karate. He speaks Greek, Spanish, and French and likes to travel with his family (they went to China this past summer).