The gap in physical and mental health between rich and poor teens has widened across North America and Europe, a Canadian researcher has found.

McGill University psychologist Frank Elgar found widening differences in the body-mass index and physical symptoms such as headache or stomach ache between socioeconomic groups aged 11 to 15 in 34 countries.

"Health inequalities in youths shape future inequities in educational attainment, employment, adult health and life expectancy, and therefore should be made a focus of health policy and surveillance efforts," Elgar concluded in Wednesday’s issue of The Lancet.

A look at average levels of health in the population alone could obscure inequities. For example, a focus on increasing teens’ physical activity could fail to consider how poorer teens lack access to recreational facilities.

Generally, as national income inequality worsened, health inequalities in four of five aspects did too.

The exception was life satisfaction scores. In high-income countries, rising national wealth between 2002 and 2010 was linked to improvements.

Adolescent obesity in high-income countries is greatly affected by the availability of unhealthy and inexpensive foods, safety and availability of parks, perceived safety of neighbourhoods and the construction of bike lanes and walkways, said John Santelli, Wendy Baldwin, and Jennifer Heitel from Columbia University Mailman School of Public Health in a journal commentary published with the study.

The onus to close the gaps in social and health-care disparities will need "efforts of public health, enlightened political leadership, the economic development sector, empowered communities, and youth themselves," they concluded.

The research was supported by the Canadian Institutes for Health Research, the Social Sciences and Humanities Research Council of Canada and the Canada Research Chairs program.