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Family, friends can influence weight and mood, from Harvard Men's Health Watch

Social interactions have ripple effects on weight and mood that extend far beyond household and family units, reports the December 2011 issue of the Harvard Men’s Health Watch.

Weight: Two of every three Americans are overweight or obese. There are many explanations for our expanding waistlines, starting with lack of exercise and excessively large portions of calorie-dense prepared and processed foods. But an interesting study suggests that social interactions may also play a role.

Researchers from Harvard and the University of California investigated 12,067 people who had been evaluated medically on multiple occasions from 1971 to 2003 as part of the Framingham Heart Study. They found that if one sibling became obese during the study, the chance that another sibling would become obese increased by 40%.

Genetics might account for some of the parallel weight gain in siblings, but not for the fact that if a spouse became obese, the likelihood that the other spouse would follow suit jumped by 37%.  That’s no surprise, since spouses share meals and may have similar exercise habits — but scientists also found that if a person had a friend who became obese, his chance of growing obese rose by 57%.

Scientists suspect a major factor is that a social network influences what its members perceive as normal and acceptable. If a man sees his friends become obese over time, he may accept weight gain as natural, even inevitable.

Mood: The Framingham Heart Study’s database also served as the foundation for a study of happiness. In this case, 4,739 people who were tracked between 1983 and 2003 served as the primary study population. Together, these subjects reported a total of 53,228 social ties to family, friends, neighbors, and coworkers. Detailed medical and psychological information was available for many of the Framingham volunteers.

The researchers used the Center for Epidemiological Studies Depression Scale to evaluate happiness at the start of the study and at subsequent follow-up examinations. Researchers looked at changes in mood over time.

The Framingham study confirmed many earlier findings about the factors that determine a person’s happiness. But it added an unexpected finding: happiness can also spread more diversely and broadly across social networks.

The scientists found that if one spouse became happy, the likelihood that the other spouse would become happy increased by 8%. Siblings who became happy increased the other sibling’s chance of becoming happy by 14%. In fact, the spread of happiness seemed to reach across at least three degrees of separation, spreading, for example, from a friend to the friend of a friend and then to the friend of that friend. However, the impact diminished with each degree of separation, and even within first-degree contacts, it began to wane after six to 12 months.

If doctors learn to harness the benefits of natural social networks to spread healthful habits, positive attitudes, and wise lifestyle choices through communities, they may be able to improve public health. This new area of research is worthy of further study, so for now, call it a network in progress.

Read the full-length article: “Social networks and health”

Also in this issue of the Harvard Men's Health Watch

  • Medical radiation: Too much of a good thing?
  • Social networks and health: Communicable but not infectious
  • On call: Acetaminophen and prostate cancer

More Harvard Health News »

About Harvard Health Publications

Harvard Health Publications publishes four monthly newsletters--Harvard Health Letter, Harvard Women's Health Watch, Harvard Men's Health Watch, and Harvard Heart Letter--as well as more than 50 special health reports and books drawing on the expertise of the 8,000 faculty physicians at Harvard Medical School and its world-famous affiliated hospitals.