This common characteristic may be as big a risk to your health as smoking

Being isolated from others isn't just lonely - it may increase your chances of an early death.

Social interactions play an important role in health. In fact, studies have found that a lack of social connections can increase the risk of death by at least 50%, and in some circumstances, by more than 90%.

That's similar to the risk caused by smoking, and higher than that from obesity or lack of exercise.

But we still don't know exactly how social isolation affects the body, when the effects occur, and how long they last.

Tracking social relationships and health

In a new study, scientists looked at four studies that tracked thousands of people from adolescence to old age, to determine how social interactions impacted health.

The aim was "to examine how social relationships 'get under the skin' to affect physiological well-being as individuals age," the researchers wrote in the study, which was published Monday in the journal Proceedings of the National Academy of Sciences.

To measure how socially connected a person was, researchers asked people about the structure and quantity of their relationships, which they referred to as "social integration," as well as the quality of their relationships, as measured by the amount of "social support" (e.g. how well your friends or family understand and care about you) or "social strain" (e.g. how much they criticize you or get you down).

The studies also took several physical measurements, including levels of C-reactive protein - a marker of inflammation - blood pressure, waist circumference, and body mass index.

The researchers compared these social and physical measures at several stages of people's lives, including adolescence, young adulthood, middle adulthood, and late adulthood.

The dangers of isolation

The results revealed a clear connection between the amount of social connections a person had in early and late life and their physical health.

Specifically, social isolation increased the risk of inflammation in adolescence by the same amount as not exercising, the researchers found. A poor social life also increased the risk of high blood pressure in old age even more than risk factors like diabetes.

The results point to the fact that social relationships start having an impact on health early in life, and those effects extend to later in life.

The findings are in line with those of another major longitudinal study known as the Harvard Study of Adult Development. That study, which followed two groups of men in Boston for 75 years, found that men who reported having more close, healthy relationships tended to be happier and healthier than their lonelier comrades.

And a wealth of other research suggests that loneliness can interfere with mental functioning, sleep, and well-being, which in turn increases the risk of illness and death.

Of course, many other factors are involved in health and longevity, such as diet, physical activity, and genetics.

But intervening and boosting social relationships could be one way to ward off some chronic diseases and lead to longer lives, the researchers suggest.

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