The potentially harmful effects of loneliness and social isolation on health and longevity, especially among older adults, are well established. For example, in 2013 I reported on research finding that loneliness can impair health by raising levels of stress hormones and inflammation, which in turn can increase the risk of heart disease, arthritis, Type 2 diabetes, dementia and even suicide attempts.

Among older people who reported they felt left out, isolated or lacked companionship, the ability to perform daily activities like bathing, grooming and preparing meals declined and deaths increased over a six-year study period relative to people who reported none of these feelings. Writing for The New York Times’s department The Upshot last December, Dr. Dhruv Khullar, a physician and researcher at Weill Cornell Medicine in New York, cited evidence for disrupted sleep, abnormal immune responses and accelerated cognitive decline among socially isolated individuals, which he called “a growing epidemic.”

As research moves forward on these topics, scientists are gaining a more refined understanding of the effects of loneliness and isolation on health. They are also looking into factors such as who is likely to be most seriously affected, and what kinds of interventions may reduce the associated risks.

There are some surprising findings. First, though equivalent in risk, loneliness and social isolation don’t necessarily go hand-in-hand, Julianne Holt-Lunstad and Timothy B. Smith, psychologist-researchers at Brigham Young University, have pointed out.