Loneliness at a problematic level is widespread in many countries, finds an analysis of evidence from 113 countries and territories during 2000-19 published by The BMJ today.

The findings identify important data gaps, particularly in low and middle-income countries, and substantial geographical variation in loneliness, with northern European countries consistently showing lower levels compared with other regions.

Existing evidence shows that loneliness not only affects mental health and wellbeing, it is also linked to a range of physical health problems and early death.

A recent estimate by US researchers suggests that one-third of the population in industrialized countries experience loneliness, and one in 12 people experiences loneliness at a level that can lead to serious health problems. But it's still unclear how widespread loneliness is on a global scale.

So a team of Australian researchers led by the University of Sydney set out to summarise the prevalence of loneliness globally to help decision makers gauge the scope and severity of the problem.

They trawled research databases and found 57 observational studies reporting national estimates of loneliness from 113 countries or territories during 2000-19.

Data were available for adolescents (12-17 years) in 77 countries or territories, young adults (18-29 years) in 30 countries, middle-aged adults (30-59 years) in 32 countries, and older adults (60 years or older) in 40 countries.

Data coverage was notably higher in high-income countries (particularly Europe) compared with low and middle-income countries.

Overall, 212 estimates for 106 countries from 24 studies were included in the meta-analysis. For adolescents, pooled prevalence of loneliness ranged from 9.2% in South-East Asia to 14.4% in the Eastern Mediterranean region.

For adults, meta-analysis was conducted for the European region only, and a consistent geographical pattern was found for all age groups.

For example, the lowest prevalence of loneliness was consistently seen in northern European countries (2.9% for young adults; 2.7% for middle-aged adults; and 5.2%, for older adults) and the highest in eastern European countries (7.5% for young adults; 9.6% for middle-aged adults; and 21.3% for older adults).

Data were insufficient to make conclusions about trends of loneliness overtime on a global scale, but the researchers point out that even if the problem of loneliness had not worsened during their search period (2000-19), covid-19 might have had a profound impact on loneliness. In this context, they say "our review provides an important pre-pandemic baseline for future surveillance."

They acknowledge their review was subject to limitations, such as different sampling procedures and measures adopted by studies. And they note that the data gaps in low and middle-income countries raise an important issue of equity.

However, considering the negative effects of loneliness on health and longevity, the authors say their findings reinforce the urgency of approaching loneliness as an important public health issue.

"Public health efforts to prevent and reduce loneliness require well-coordinated ongoing surveillance across different life stages and broad geographical areas," they write.

"Sizeable differences in prevalence of loneliness across countries and regions call for in-depth investigation to unpack the drivers of loneliness at systemic levels and to develop interventions to deal with them," they conclude.

Loneliness is costly to individuals and society and should be a political priority, argue Roger O'Sullivan at the Institute of Public Health in Ireland and colleagues, in a linked editorial.

They point out that the pandemic has dispelled the myth that loneliness is just an older person's problem and say public health interventions must now take this into account and take a life course approach.

This means addressing the social and structural factors that influence risk of loneliness, including poverty, education, transport, inequalities, and housing – as well as increasing protective measures, such as public awareness campaigns that deal with stigma and stereotypes around loneliness, valuing community involvement and participation.