(Photo: Marc Kjerland/Flickr)

Social isolation is bad for your health. In fact, even living alone increases your risk of illness and death by about 20 percent, and a lack of friends or strong family ties ups your risk by half. Now, researchers have found, social isolation early in life can have substantial lasting impacts on health.

"Full social participation is such a fundamental human need that research since the 1900s has found the lack of social connections increases the odds of death by at least 50%," write Yang Claire Yang, National Academy of Sciences member Kathleen Harris, and their colleagues in Proceedings of the National Academy of Sciences. When more complicated measures of social relationships are taken into account, social isolation can nearly double the odds of ill health and death, putting it on par with smoking and a sedentary lifestyle.

Working to build new relationships and improve old ones could be an effective strategy to prevent, delay, or at least lessen the the effect of disease late in life.

Yet the details are less clear. How long do the effects of social isolation last? How does having fewer friends or fewer close relationships affect health? To find out, Yang and her team looked to four major studies—the National Longitudinal Study of Adolescent to Adult Health, Midlife in the United States (MIDUS), the Health and Retirement Survey, and the National Social Life, Health, and Aging Project—with a total of nearly 15,000 participants ranging in age from early adolescence to elderly retirees. Each of the four surveys collected information on social integration—factors like the number of friends a person has—as well as four physiological measures of health: blood pressure, body mass index, waist circumference, and C-reactive protein level, an indicator of inflammation. (Inflammation is important, the researchers point out, because chronic inflammation is now thought to be connected to a wide range of mental and physical ailments.)

Generally speaking, people with more friends, higher quality relationships, and so on had lower blood pressure and BMI measurements, smaller waists, and less inflammation than others, but with some interesting variation across age groups. For example, social isolation increased blood pressure and inflammation in adolescence and young and late adulthood. In contrast, the effect on BMI and waist circumference was only apparent in adolescence. There was no evidence social integration had an effect on middle aged people's health, though that may reflect the set of people interviewed as part of the MIDUS study—80 percent of whom had at least weekly contact with family and friends—rather than real physiological differences.

"Our findings suggest the early emergence and continuity of the physiological impacts of social relationships across the life course" the team writes. In theory, then, working to build new relationships and improve old ones could be an effective strategy to prevent, delay, or at least lessen the effect of disease late in life.

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