Nearly half of young adults across eight countries report feeling lonely - and those who do face much higher likelihood of depression and anxiety, according to a new international study led by researchers at the Washington University in St. Louis School of Public Health.
Across all eight countries, nearly four in 10 adults reported feeling lonely. Among those ages 18-24, that figure rose to nearly one in two, compared with about 30% of adults 55 or older.
Women, individuals with lower income or education, unmarried people and urban residents also reported higher levels of loneliness. People who reported loneliness had almost three times the odds of meeting screening criteria for depression and nearly four times the odds of meeting screening criteria for generalized anxiety.
Prevalence of depression and anxiety varied substantially across countries, ranging from 3.4% in India to 15.8% in Brazil. However, the association between loneliness and both conditions was consistent across national contexts.
The study, "Loneliness, Depression and Generalized Anxiety Across Eight Countries," published Feb. 5 in Social Psychiatry and Psychiatric Epidemiology, was led by Salma Abdalla, MBBS, DrPH, an assistant professor at the WashU School of Public Health. Sandro Galea, MD, DrPH, the school's Margaret C. Ryan Dean, served as senior author. Galea also is the Eugene S. and Constance Kahn Distinguished Professor in Public Health and vice provost for interdisciplinary initiatives at WashU.
Depression and anxiety are among the leading causes of disability worldwide, affecting hundreds of millions of people and limiting their ability to work, study, care for family or fully participate in daily life. Between 2010 and 2023, anxiety disorders increased by about 60% and depressive disorders by about 26%, the authors noted.
By 2023, depression and anxiety accounted for more than 110 million combined years of healthy life lost worldwide. The new study underscores loneliness as a powerful correlate of mental health risk across diverse national contexts.
The team analyzed nationally representative survey data from 7,997 adults in Brazil, France, India, Indonesia, Nigeria, the Philippines, Turkey and the United States. The survey was conducted between November 2023 and February 2024 in multiple languages and underwent rigorous translation review to ensure accuracy across countries. Researchers collected roughly 1,000 responses per country.
Researchers examined how loneliness and mental health varied by age, gender, education, income, marital status, urban or rural residence and country. They also accounted for whether participants had received a clinical diagnosis of depression, anxiety or post-traumatic stress disorder in the past year.
"This study shows that loneliness is not a marginal issue - it is common across countries and strongly linked to serious mental health outcomes," Abdalla said. "Even after accounting for demographic differences and prior diagnoses, the association between loneliness and depression and anxiety remained strong."
About 9% of respondents met screening criteria for depression and roughly 6% for generalized anxiety.
In 2023, the World Health Organization declared loneliness a global public health concern and launched a commission focused on strengthening social connection. That same year, the U.S. surgeon general warned that loneliness carries serious health risks, comparing its mortality impact to smoking 15 cigarettes a day. Research increasingly links loneliness not only to mental health challenges but also to physical health risks, including heart disease, stroke and early death.
The findings add new cross-national evidence about how loneliness relates to depression and anxiety. Prior international surveys have examined loneliness in specific regions, but fewer studies have evaluated its relationship to depression and anxiety across multiple countries using standardized measures. Much of the existing research has focused on single countries, relied on data collected before 2020 or centered primarily on adults over age 50.
A growing body of research suggests the relationship may be reinforcing. Loneliness can heighten stress, reduce social support and disrupt sleep and other protective behaviors, increasing vulnerability to depression and anxiety. In turn, symptoms of depression and anxiety may lead to social withdrawal and negative expectations about relationships, further deepening loneliness.
"These findings suggest that strengthening social connection should be central to mental health policy and treatment efforts," Galea said. "While this study cannot determine cause and effect, the consistency of the evidence underscores loneliness as a serious public health concern."
The authors noted that further longitudinal and intervention research is needed to clarify how loneliness and mental health influence one another and to identify strategies that effectively reduce risk.
