Research suggests that more than 11 million Americans age 50 and over often feel isolated, left out, or lonely.

A new study by scientists at the University of Chicago shows that people who were lonely had blood pressure readings as much as 30 points higher than those who weren't. The effect was as great as being overweight or sedentary.

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.

Harvard doctors linked loneliness in men with increased blood levels of inflammatory markers associated with heart disease. And a Duke University study found increased risk of death in isolated patients with heart disease.

The magnitude of the association in people age 50 and over is "stunning," according to Louise Hawkle, the Chicago study's lead author.

The study says something important about social connection in our everyday lives. The researchers say part of living a healthy life is paying attention to friends and family.

The doctors recommend joining a club or doing volunteer work to increase contact with people.