Loneliness was strongly linked to high blood pressure even when conventional risk factors such as weight, smoking and alcohol consumption were also considered.

The loneliest people studied had blood pressure readings as much as 30 points higher than those who weren't lonely, suggesting that loneliness can be as bad for the heart as being overweight or inactive, the researchers said.

"The magnitude of this association is quite stunning," said University of Chicago scientist Louise Hawkley, the study's lead author.

With earlier research suggesting that more than 11 million Americans over 50 often feel isolated, left out or lacking companionship, the study could have substantial public health implications if it can be shown that reducing loneliness can lower people's blood pressure, said Richard Suzman, director of a behavioral research program at the National Institute on Aging, which helped fund the study.

Increased Risk of Death

Hawkley said the findings hint that one strategy for treating high blood pressure might be to get more involved, "do volunteer work, make yourself useful."

The study of 229 Chicago-area men and women ages 50 to 68 appears in the March issue of the journal Psychology and Aging.

The results build on earlier research by co-author John Cacioppo, who found that in younger adults loneliness was linked with blood vessel problems that could lead to high blood pressure.

Last year, Harvard research linked loneliness in men with increased blood levels of inflammatory markers associated with heart disease. And a study at Duke University found an increased risk of death in socially isolated patients with heart disease.

Importance of Social Connection

The research "says something about the importance of social connection in our everyday lives," said Cacioppo, a psychology professor who works with Hawkley at the university's cognitive and social neuroscience center. "Part of living a healthy life is paying attention to friends and family."

As people grow old, friends and family move away, retire, fall ill and die, "so there has to be a replenishment of social relationships," Suzman said.

Study participants were asked on a 20-item questionnaire to rate the degree to which they lacked companionship. Slightly more than half the study participants were considered at least moderately lonely and had higher blood pressure than those who felt less lonely.

The strongest link was in the 15 percent of participants who were highly lonely. Their systolic blood pressure -- the upper number in a blood pressure reading -- was 10 to 30 points higher than in non- lonely people.

Loneliness was strongly linked to high blood pressure even when conventional risk factors such as weight, smoking and alcohol consumption were also considered.