The study, published in the Proceedings of the National Academy of Sciences, builds on previous research that shows that aging adults live longer if they have more social connections. It not only provides new insights into the biological mechanisms that prolong life, but also shows how social relationships reduce health risk in each stage of life.

Researchers found that the sheer size of a person’s social network was important for health in early and late adulthood. In adolescence, social isolation increased risk of inflammation by the same amount as physical inactivity, while social integration protected against abdominal obesity. In old age, social isolation was actually more harmful to health than diabetes on developing and controlling hypertension.

In middle adulthood, the number of social connections didn’t matter as much as what those connections provided in terms of social support or strain.

Kathleen Mullan Harris, James Haar Distinguished Professor at UNC-Chapel Hill and faculty fellow at the Carolina Population Center (CPC), explained:

The relationship between health and the degree to which people are integrated in large social networks is strongest at the beginning and at the end of life, and not so important in middle adulthood, when the quality, not the quantity, of social relationships matters.

The researchers used data from four nationally representative surveys of the U.S. population that covered the lifespan from adolescence to old age. They evaluated three dimensions of social relationships: social integration, social support, and social strain. They then studied how social relationships were associated with four markers shown to be key markers for mortality risk: blood pressure, waist circumference, body mass index, and circulating levels of C-reactive protein (which is a measure of systemic inflammation).

One of the four nationally representative surveys was part of The National Longitudinal Study of Adolescent to Adult Health (Add Health), which is the largest, most comprehensive data used by researchers to study how social relationships, behavior, environment, and biology interact to shape health in adolescence and influence well-being throughout adulthood.

Yang Claire Yang, a professor at UNC-Chapel Hill, CPC fellow and a member of the Lineberger Comprehensive Cancer Center, said of the findings:

We studied the interplay between social relationships, behavioral factors and physiological dysregulation that, over time, lead to chronic diseases of aging — cancer being a prominent example. Our analysis makes it clear that doctors, clinicians, and other health workers should redouble their efforts to help the public understand how important strong social bonds are throughout the course of all of our lives.

Harris said of the research: