It's enough to make a person sick—and loneliness does. In the 1980s and '90s, Janice Kiecolt- Glaser, PhD, professor at Ohio State University College of Medicine, demonstrated that lonely individuals had poorer immune function than the nonlonely. In 1995 Cacioppo and his team started examining the effects of social isolation on an individual's circulatory system. Among the college students, both the lonely and nonlonely had similar blood pressure levels. But when Cacioppo and his researchers looked closer, they discovered that the measure of the constriction of the blood vessels, the total peripheral resistance (TPR), differed in the two groups. Whenever Cacioppo tested them, the lonely college students had higher TPR, a sign of stress.

Both groups were young, which means their physiological resilience tended to be pretty high—the heart is working fine and the body's many systems are compensating for the increased TPR in the lonely. But in older adults, increased TPR contributes to high blood pressure. "That led us to hypothesize that as the students grew older, we'd see higher blood pressure," says Cacioppo.

Cacioppo has not done a longitudinal study with those 20-somethings, but his older group, currently in the last year of a five-year Chicago Health, Aging, and Social Relations Study (CHASRS), has reached the typical age for arterial stiffening. He and his team have discovered an association between loneliness and high blood pressure. Normal systolic blood pressure is less than 120 mmHg (millimeters of mercury, the standard unit of measurement). Looking at the CHASRS participants, Cacioppo says, "we found that as they get older, there's approximately a .7 mmHg increase a year per what's called standard deviation of loneliness." That doesn't sound like much, but let's assume at age 20 you have normal blood pressure. If you're chronically lonely, by the time you're 50, using Cacioppo's rate of increase, you could be hypertensive. And by the time you're 65, you could be seriously hypertensive, with an even greater risk of heart attack and stroke.

Cacioppo's team thinks one of the reasons for increased TPR might have to do with something they'd noticed while studying the restorative process of sleep among college students in the '90s. "We found that lonely people sleep less efficiently and complain about more daytime dysfunction and sleepiness," says Cacioppo. "We found it in the young adults and in the older adults. So this process that detoxifies isn't there."

As in the other studies, his team has taken into account age, gender, ethnicity, income, education, marital status, family history, level of physical activity, depressive symptomatology, social support—and this association of poor restorative process and increased TPR appears only in the lonely. In the older adults, Cacioppo found a link between poor restorative process and high blood pressure. It will take more years of study to prove that loneliness is the cause, but the association is compelling. Richard Suzman, PhD, of the National Institute on Aging, a government agency that has helped fund Cacioppo's research, wrote in an e-mail that the findings "suggest that we will pay more attention to the experience in the future, including testing whether interventions to reduce the experience of loneliness also reduce blood pressure in a cost-effective manner."

Cacioppo, Russell, Weiss, and Suzman are not aware of anyone specifically looking into how to lower blood pressure by reducing loneliness. Part of the difficulty, Cacioppo notes, is that since the increase in blood pressure is so incredibly subtle, it takes decades to see the results of chronic loneliness in hypertensive blood pressure. Another complication is accounting for the 50 percent of people who are lonely one year but not the next (though many become so again). Researchers are still trying to identify more definitively what the predictors of loneliness are—and what possible interventions might be helpful.

Teasing out answers would be an enormously tricky undertaking, but there are significant reasons why it might be important to try: Census information suggests that by 2010, 31 million people will be living alone, up from 18 million 25 years ago. And remember Daniel Russell's older generation of Iowans—those over 65 who were less lonely than younger people? Researchers thought that could be the result of wisdom or lowered expectations or desire for the peace and quiet of retirement, but Russell is finding that as boomers move into their retirement years, they are reporting higher levels of loneliness than the group measured in the 1980s. Maybe those who weathered the Great Depression were more grateful for what they had—a house, grandchildren, Social Security—than today's soon-to-be seniors? If the Greatest Generation was indeed a one-off, an aberration, followed by the boomers, and since people are marrying later and an increasing number of households are being headed by single parents, the number of lonely could shoot up.


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