The World Health Organization recommends no more than two to three hours per day of sedentary time for youth. However, adolescents worldwide are spending an average of 8 to 10 hours per day engaging in sedentary activities such as watching television, using electronic devices, playing video games and riding in motorised vehicles, according to a multinational study published in the Nov. 29, 2024 issue of the International Journal of Behavioral Nutrition and Physical Activity.

The most notable finding of the study, led by principal investigator James F. Sallis, PhD, distinguished professor at the Herbert Wertheim School of Public Health and Human Longevity Science at the University of California San Diego, and colleagues from 14 countries, found that simply having a personal social media account was linked with higher total sedentary time in both males and females. Social media was also related to more self-reported screen time.

"Although there is great concern about the negative effects of social media on youth mental health, this study documents a pathway for social media to harm physical health as well," said Sallis, who is also a professorial fellow at the Australian Catholic University.

"These findings are concerning, as excessive sedentary behaviour has been linked to a range of health problems, including obesity, diabetes and mental health issues."

Researchers analysed accelerometer data from 3,982 adolescents aged 11 to 19 and survey measures of sedentary behaviour from 6,302 participants in the International Physical Activity and the Environment Network (IPEN) Adolescent Study, which covered 15 geographically and culturally diverse countries across six continents.

The number of electronic devices within a home, how many adolescents had their own social media accounts and neighborhood walkability were significantly different across countries.

For example, adolescents from India had an average of 1.2 electronic devices in the bedroom and 0.5 personal electronic devices, while the average number of such devices in Denmark was 4.2 and 2.3, respectively. In India and Bangladesh, fewer than 30% of adolescents reported having their own social media account, compared to higher socio-economic status countries where it was over 90%.

Parents reporting on walkability identified Australia as having high access to parks, while Nigerian parents reported no access, and parents in Bangladesh and India reported poor access. Traffic was a concern among parents in Brazil, Malaysia, Bangladesh, India, and Israel, and concerns about crime were high in the first three countries.

Adolescents who reported less recreational screen time lived in walkable neighbourhoods and had better perceptions of safety from traffic and crime than others. Girls who lived in neighbourhoods designed to support physical activity were less likely to be sedentary.

Despite differences in culture, built environments and extent of sedentary time, patterns of association were generally similar across countries, said the study's lead author Ranjit Mohan Anjana, M.D., Ph.D., of Dr. Mohan's Diabetes Specialties Centre and Madras Diabetes Research Foundation in India.

"Together, parents, policymakers and technology companies can work together to reduce access to screens, limit social media engagement and promote more physical activity, thus helping adolescents develop healthier habits and reduce their risk of chronic diseases," said Anjana.

The study's findings have significant implications for public health policy and highlight the need for further research into the causes and consequences of sedentary behaviour among teenagers.