The greatest apparent predictors of loneliness are the size of a person's social network and physical isolation, according to the survey of over 3,000 U.S. adults age 45 and older by the AARP Foundation, which used the UCLA Loneliness Scale that is utilized widely in scientific literature.
The survey also found that infrequent sex and inadequate sleep are associated with loneliness.
Among the most striking findings is that people who never speak to their neighbors are nearly twice as likely to be lonely than those who have talked to neighbors.
“As a society, it’s important that we recognize that social isolation and loneliness are widespread public health issues, particularly among older and low-income adults,” Lisa Marsh Ryerson, president of the AARP Foundation, told ABC News.
“Social isolation and loneliness have been found to have health risks equivalent to those of obesity or smoking up to 15 cigarettes per day,” Ryerson continued. “Yet, very few individuals have ever talked to their physicians about these issues.”
Social isolation can be measured objectively through the number of people in a person’s social network and how frequently they’re in contact. Loneliness, however, is more subjective -- how a person perceives their experience, and whether they feel a lack of connectedness or sense of belonging. The survey asked questions about both.
The authors released the study to coincide with the upcoming National Good Neighbor Day on Friday, Sept. 28, which was first proclaimed by President Jimmy Carter in 1978.
“Understanding, love, and respect build cohesive families and communities," Carter said in his proclamation. "The same bonds cement our nation, and the nations of the world.”
The AARP survey reinforces results of a large study conducted by the health insurer Cigna earlier this year, which found that loneliness is at epidemic levels among American adults. While the Cigna study found that loneliness is most common among young adults, age 18 to 22, the new survey finds that that loneliness is also a problem for older adults.
In the AARP survey, forty-six percent of respondents aged 45 to 49 reported loneliness, compared to 37 percent who are in their 50s, 36 percent in their 60s, and 24 percent in their 70s.
The authors of the survey caution that they cannot draw conclusions on the causes of loneliness, but they identified several conditions that seem linked.
Infrequent sex and inadequate sleep are among the factors that appear to be associated with loneliness.
Among people who have sex at least once per week, 25 percent report being lonely compared to 37 percent of those who have sex once a month or less, and 43 percent for those who are sexually inactive. Similarly, among people who get five to eight hours of sleep a night, 34 percent are lonely, compared to 59 percent who get four hours of sleep or less.
Perhaps surprisingly, those who drink alcohol to any extent are slightly less likely to be lonely than those who do not, 33 percent versus 38 percent.
Income is also associated with loneliness, the survey found. Among people earning less than $25,000 a year, 50 percent are lonely, compared to 31 percent of those with income over $50,000 per year.
Among people who identify as lesbian, gay, bisexual, transgender, or queer, 49 percent are lonely compared to 35 percent of those who do not identify as such.
Unsurprisingly, all forms of communication with friends and siblings are associated with decreased loneliness, but the mode of communication is important. Those who see friends in person at least once a month are less likely to be lonely than those who communicate by email, text or video.
But, the relationship between social media and loneliness is complex, according to the survey results.
Thirty-six percent of people who opt out of social media entirely said they are lonely, a similar rate to those who use social media somewhat regularly: 31 percent for those who use social media once a week or more, and 35 percent among those who use it once or twice a month. People who use social media infrequently, once or twice a year, have the highest prevalence of loneliness, 42 percent.
The AARP has suggestions on how individuals can ward off loneliness, including simply "looking out for each other,” as Ryerson put it.
Other suggestions include inviting a neighbor over for coffee or tea; checking in on elderly neighbors and offering to run errands for them; organizing a potluck for your block (or the whole neighborhood); asking a neighbor to join you for a walk; and volunteering with a meal-delivery service.
“Our goal is to raise awareness on these issues, to remind each of us that we ourselves could be at risk for loneliness, but certainly, by living in a community, we are also part of the solution,” Ryerson said.
Dr. Nicky Mehtani is an internal medicine physician at Johns Hopkins Hospital and a part of the ABC News Medical Unit.