From an article by David Loxterkamp in the British Medical Journal:

“Our social connections also seem to have a strong influence on health. In 2007, Nicholas Christakis and James Fowler tracked the social connections of more than 12 000 residents of Framingham, Massachusetts, over three generations (1).

They found that the risk of becoming obese increased by 45% if a friend became obese, by 20% if the friend had a friend who became obese, and by 10% if a friend of that friend’s friend gained weight, thus establishing the rule of ‘three degrees of influence.’

They subsequently found that smoking cessation and the spread of happiness also followed the three degree rule (2, 3). In powerful ways, we mimic the behaviours and absorb the values of others, especially those we like.”

Reference

BMJ 2013;347:f5539

References Used in the Article

1. Chistrakis, N,A, & Fowler, J.H. (2007) The Spread of Obesity in a Large Social Network over 32 Years. New England Journal of Medicine. 357, pp.370-379.
2. Christakis, N.A. & Fowler, J.H. (2008) The Collective Dynamics of Smoking in a Large Social Network. New England Journal of Medicine. 358, pp.2249-2258.
3. Fowler, J.H. & Christakis, N.A. (2008) Dynamic Spread of Happiness in a Large Social Network: Longitudinal Analysis over 20 years in the Framingham Heart Study. British Medical Journal. 337, pp.a2338.