More humans are alive today than ever before, and yet around the world, people are still feeling alone a lot of the time.
Past studies in the industrialized world have suggested loneliness is on the rise, but without historical data on the issue, it's hard to say how present-day numbers compare over time or across geographical regions.
"It's a commonly held belief that around 1 in 12 people experience loneliness at a level that can lead to serious health problems, however, the source of such data are unclear and researchers have never established how widespread loneliness is on a global scale," says epidemiologist Melody Ding from the University of Sydney.
"That is why we were interested in conducting the review."
Ding and her colleagues have therefore pulled together 57 observational studies on loneliness from 113 countries or territories between 2000 and 2019.
The authors hope to use the findings as a pre-pandemic baseline to monitor feelings of lonesomeness going forward.
Because loneliness is associated with mental, emotional, and physical well-being, the findings could help reveal emerging issues in public health that must be better addressed.
Global loneliness estimates were mostly available for adolescents, and findings among 77 nations suggest the issue can range from 9.2 percent in South-East Asia to 14.4 percent in the Eastern Mediterranean region.
Unfortunately, for adults, there was only enough data for the meta analysis to hone in on the European region.
In this corner of the world, the authors once again found geographical differences. Northern European nations had the lowest rates of loneliness, with only 2.9 percent of young adults experiencing the negative emotion and 2.7 percent of middle-aged adults feeling the same. Older adults, over the age of 60, experienced lonesomeness at a higher rate of 5.3 percent.
Eastern European countries, on the other hand, showed more signs of loneliness than anywhere else in Europe. Young adults in Eastern Europe reported feelings of loneliness at a rate of 7.5 percent, while middle aged adults reported feelings of loneliness at a rate of 9.6 percent. Older adults in this part of Europe, meanwhile, were the loneliest of the lot, coming in at a worrisome 21.3 percent.
The data can't tell us why Eastern Europe appears to have a more lonely populace overall, but one study included in the review suggests the effect is due to worse health outcomes, healthcare services, and social support.
Welfare systems and social security schemes are commonly put forward as explanations for reduced loneliness, and northern European countries tend to excel in these areas. Further research will be needed to confirm the hypothesis.
"Understanding loneliness as a global health issue requires data from most countries – however, data are lacking for most regions outside of Europe," the authors write.
"Meanwhile, the lack of repeated measurements limited our conclusions about temporal trends."
Meaning we have no idea how these numbers compare to decades gone by. If the problem of loneliness is worsening, it's important public health experts and policymakers know so they can take appropriate action.
Never has that been more important than now. The World Health Organization has warned that the social isolation measures keeping the dangerous SARS-CoV-2 virus at bay will also probably lead to increased levels of loneliness, depression, harmful alcohol and drug use, and self-harm or suicidal behavior.
The current review could find no low-income countries with nationally representative data on loneliness in adults, due to limited resources and competing priorities.
These major data gaps are leaving us blind to a common and global issue, which can have impacts on mental health and physical health at all ages. Social isolation and loneliness have actually been associated with a rise in the risk of early death, on a scale equivalent to smoking cigarettes. Yet it's unclear what mechanism is driving that fatal relationship.
Census data in the United States has found more young and middle-aged people today are living alone than in previous years. But in the European review it seems older adults, over the age of 60, are those most likely to suffer feelings of severe loneliness.
The differing results among nations suggest the age pattern of loneliness might be context specific, but we need more data to say for certain.
When our lives literally depend on connecting with others, it's shocking that more research on loneliness and isolation hasn't been done.
Now, the global pandemic has made us aware of the issue like never before, and researchers like Ding are scrambling to make sense of the little information we have so we can make informed decisions about the future.
"A public health approach to loneliness means confronting the social and structural factors that influence risk of loneliness across the life course, including poverty, education, transport, inequalities, and housing, and implementing policies to address them," a team of Irish and UK public health experts writes in an editorial linked to the new research.
"It is important to facilitate healthy social choices, making it easier to connect with others in the community, change work environments, and increase opportunities for building trust and social capital."
The study was published in BMJ.