Although researchers began looking at the effects of isolation on people in the late 1970s, studies on isolation have become more common in the past 15 years. Discovering how isolation contributes to the hunger, housing and income problems many seniors face — and seeking workable solutions to those problems — is the task of AARP Foundation's Isolation Impact team. Below is a sample of the research findings on isolation:

Forty percent of people age 65 and over live alone. — Photo by Dex Image/Getty Images

It's Not a Disease

1. The need for social connection is rooted in our basic urge to survive, and is wired into the neurons in our brains. As we evolved from relatively weak, small mammals, we became a dominant species because of our ability to form social connections and because our brains expanded to meet this need.

2. Isolation is not a mental disease, but a situation that can and does lead to health changes. Health studies show that older, isolated people have much higher rates of mortality from breast cancer, high blood pressure, heart disease and other chronic diseases. According to researchers, being isolated is just as bad for people as smoking and is worse than being obese.

How Isolation Develops

3. Caregiving often triggers isolation. The number of people providing unpaid care for a friend or relative rose 23 percent — to 54 million — from 2004 to 2009, and that number continues to grow. Caregivers often work by themselves, and more than half (53 percent) say they have less time for friends and family. All too often, they don't call doctors when they are sick, and they have little or no time to exercise or eat well. Studies show that up to 70 percent of caregivers have clinically significant symptoms of depression.

4. People don't have as many close friends as they used to. In 1985, researchers at the University of Arizona and Duke University asked people how many "close contacts" they had — friends who they could confide in — and their overall average was three. Nearly 20 years later, in 2004, that number had declined to two. Even worse, the number of people who had no close contacts rose from 10 percent to 24.5 percent — nearly one in every four people had no friends to confide in.

Next: Other factors, plus a bit about our research. »