In another study, published in The New England Journal of Medicine in 1984, researchers at the Health Insurance Plan of Greater New York found that among 2,320 men who had survived a heart attack, those with strong connections with other people had only a quarter the risk of death within the following three years as those who lacked social connectedness.

Researchers at Duke University Medical Center also found that social ties can reduce deaths among people with serious medical conditions. Beverly H. Brummett and colleagues reported in 2001 that among adults with coronary artery disease, the mortality rate was 2.4 times higher among those who were socially isolated.

In a column I wrote in 2013 called “Shaking Off Loneliness,” I cited a review of research published in 1988 indicating that “social isolation is on a par with high blood pressure, obesity, lack of exercise or smoking as a risk factor for illness and early death.”

People who are chronically lacking in social contacts are more likely to experience elevated levels of stress and inflammation. These, in turn, can undermine the well-being of nearly every bodily system, including the brain.

Absent social interactions, blood flow to vital organs is likely to be reduced and immune function may be undermined. Even how genes are expressed can be adversely affected, impairing the body’s ability to turn off inflammation. Chronic inflammation has been linked to heart disease, arthritis, Type 2 diabetes and even suicide attempts.

In a 2010 report in The Journal of Health and Social Behavior, Debra Umberson and Jennifer Karas Montez, sociology researchers at the University of Texas at Austin, cited “consistent and compelling evidence linking a low quantity or quality of social ties with a host of conditions,” including the development and worsening of cardiovascular disease, repeat heart attacks, autoimmune disorders, high blood pressure, cancer and slowed wound healing.

The Texas researchers pointed out that social interactions can enhance good health through a positive influence on people’s living habits. For example, if none of your friends smoke, you’ll be less likely to smoke. According to the researchers, the practice of health behaviors like getting regular exercise, consuming a balanced diet and avoiding smoking, excessive weight gain and abuse of alcohol and drugs “explains about 40 percent of premature mortality as well as substantial morbidity and disability in the United States.”