Harvard Mental Health Letter

Infectious health behaviors

A theory about how health and emotions may spread.

People are social by nature, spending about 80% of their waking hours with family, friends, or co-workers. A spate of studies about the health impact of this web of personal relationships — or "social networks," in research parlance — suggests that friends, family members, and even friends-of-friends can "spread" particular health behaviors and emotions, just as they can spread a cold or flu virus.

Dr. Nicholas Christakis, a social scientist at Harvard University and a physician specializing in palliative care, became interested in social networks while helping patients and families make end-of-life decisions. He has collaborated frequently with Dr. James Fowler, a political scientist at the University of California, San Diego.

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