A crippling disorder that is difficult to treat strikes nearly everyone at various stages in life, and complications can contribute to heart disease, stress, emotional instability and even death. It is particularly ruthless when it hits elders, as well as adolescents, and in some cases it may be nearly impossible to cure.
It's called "loneliness."
A growing body of research reveals that for many people, lonely is normal, especially during the holiday season. It can be brought on by a number of causes:
Most of us are lonely from time to time, but "the prevalence of loneliness may be different for different ages," says Katherine Fiori, who is just finishing up her work toward a doctorate in developmental psychology at the University of Michigan in Ann Arbor. "It may be particularly prevalent among older adults, and among adolescents, and at certain points in the lifespan when people are going through different changes, like retirement," she says.
"But the prevalence and types of loneliness may differ by age."
Nowhere is that more apparent than among the elderly, according to Fiori's research. A close personal relationship with her grandparents led her into a field that many younger researchers shun, gerontology.
She was especially close to her grandmother, and when she died, Fiori says, the impact on her grandfather was very hard to watch.
"Watching my grandfather go through the process of grieving made me particularly interested in loneliness," she says.
That helped focus her attention on research she carried out a few years ago while spending a year at the Max Planck Institute for Human Development in Berlin. While there, she had access to a rich body of work called the Berlin Aging Study. For more than a decade now researchers there have been interviewing participants in the study, all of whom were at least 70 years old.
They began with 516 seniors, Fiori says. Fewer than 50 are still alive.
Combing through those interviews, she found some disturbing numbers.
Most of those senior citizens -- nearly 60 percent -- described themselves as lonely. Some felt socially isolated. Others felt emotionally lonely. Some felt both socially and emotionally out of the loop.
Surprisingly, those with the largest number of friends were among those who were hardest hit by loneliness. They found themselves not only alone in a crowd, but alone in an aging crowd. Furthermore, while they may have had many friends, they described themselves as more depressed and less satisfied with their lives than those with fewer friends.
The reason, Fiori concludes, is that success does not lie in numbers. Instead, it's how the relationship is perceived that matters.
"People can have large social networks and still feel really lonely," she says. "Even if they have a lot of people around them, they may not feel they have people they can turn to, or people they feel close to. It's really a perception."