Loneliness and social isolation have long been seen as vexing personal problems but have seldom risen to the top of anyone’s list of pressing public policy concerns.

Now, as populations age across the developed world, prominent researchers and public health officials are calling on nations to pay more attention to health risks, especially depression and cognitive decline, facing the growing ranks of chronically lonely older adults.

In a recent letter published in the Lancet, a leading medical journal, 15 experts on aging from the United States and other countries called for a unified approach to addressing loneliness and expanding social ties. They proposed more public research funding, standardized measures of loneliness and isolation, and better education about their dangers.

“We have solid evidence that social isolation is a health hazard,’’ said Boston College professor emeritus James Lubben, the founding director of its Institute on Aging and one of those who signed the letter. “It’s time for us to move this field forward with more rigorous studies that identify types of social isolation and develop different kinds of interventions.’’

Members of the group, which first convened at a summit in Belfast at the end of 2018, have taken their message to medical and public health associations over the past year and plan to step up their efforts in 2020 to bring attention to the issue.

While the terms are often used interchangeably, researchers define loneliness as a subjective negative experience stemming from lack of meaningful connections, and social isolation as a condition of those without regular contact with relatives, friends, neighbors, and outside groups.

Older people, who sometimes live far from family members or have health conditions limiting their mobility, are a primary focus of the anti-loneliness campaigners. But they’re quick to point out that not all older adults are lonely or isolated, and many younger folks are.

Government officials have begun to address the problem in recent years. The United Kingdom named the world’s first “minister for loneliness’’ in 2018. And a range of public and private efforts to help people disconnected from others are underway in the United States. In Massachusetts, for example, Middlesex District Attorney Marian Ryan is working to raise awareness of loneliness and the importance of interaction for people of all ages.

Linda P. Fried, the dean of Columbia’s Mailman School of Public Health, who chairs the International Loneliness Research Network, said a confluence of trends — including the rise of social media and increasing age segregation — are pushing seniors to society’s periphery. “We designed so much in the 20th century to create independence and autonomy,’’ Fried said. “But human beings are social animals who really need intimate personal connections and meaningful connections with family and friends, and religious and civic organizations.’’

Robert Weisman can be reached at robert.weisman@globe.com. Follow him on Twitter @GlobeRobW.