I now know why I gained more than 13 kilograms in my early 20s: I was lonely. I had left for school and a job in the Upper Midwest and I knew no one. I filled my lonely nights and days with food, especially candy, cookies and ice cream. I could not rein in my eating until I returned to New York and my family, and began dating my future husband.

Loneliness, says John T. Cacioppo, an award-winning psychologist at the University of Chicago, undermines people's ability to self-regulate. In one experiment he cites, participants made to feel socially disconnected ate many more cookies than those made to feel socially accepted.

In a real-life study of middle-aged and older adults in the Chicago area, Dr. Cacioppo and colleagues found that those who scored high on the University of California, Los Angeles, Loneliness Scale, a widely used assessment, ate more fatty foods than those who scored low.

"Is it any wonder that we turn to ice cream or other fatty foods when we're sitting at home feeling all alone in the world?" Dr. Cacioppo said in his well-documented book, "Loneliness," written with William Patrick.

He said lonely individuals tend to do whatever they can to make themselves feel better, if only for the moment. They may overeat, drink too much, smoke, speed or engage in indiscriminate sex.

A review of research published in 1988 found 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," Dr. Cacioppo wrote.

Even without the presence of unwholesome behaviors, Dr. Cacioppo and others have shown that loneliness can impair health by raising levels of stress hormones and increasing inflammation. The damage can be widespread, affecting every bodily system and brain function.

Lisa Jaremka of Ohio State University reported in January that people who are lonely have higher levels of antibodies to certain herpes viruses, indicating more activated viruses in their systems. In another study, she found higher levels of inflammation-inducing substances in the blood of lonely people.

Chronic inflammation has been linked to heart disease, arthritis, Type 2 diabetes, and even suicide attempts, Dr. Jaremka noted.

Loneliness has also been linked to cognitive decline. A Dutch study published last year in The Journal of Neurology, Neurosurgery & Psychiatry found that participants who reported feeling lonely were more likely to develop dementia than those who lived on their own but were not lonely.

The Dutch study suggests that how people perceive their situation may have a stronger impact on health than whether they live alone and lack social connections. Divorced people have reported feeling lonelier in a bad marriage than they do being single. And people who live alone may still have a large network of friends and family that helps to keep loneliness at bay.

People are fundamentally social beings who require meaningful connections with others to maximize health and well-being. Dr. Cacioppo suggests reaching out to others with "random acts of kindness": doing something that helps them physically or emotionally, maybe something as simple as complimenting a stranger's outfit or helping an old person cross the street.

"What's required," he wrote, "is to step outside the pain of our own situation long enough to 'feed' others. Real change begins with doing."

(China Daily 06/02/2013 page11)