Young people between the ages of 10 and 24 years bear more than 15% of the world’s global disease burden because of nonfatal mental health disorders, according to a new study by World Health Organization scientists.

These mental health disorders include substance abuse and account for nearly half of the disabilities in this age group. The findings, published online June 7 in the Lancet, suggest that public health strategies need to be better targeted to young people and the risks specific to them – which differ from those of the population at large (Lancet 2001 June 7 [doi:10.1016/S0140-6736(11)60512-6]).

Fiona M. Gore of WHO’s department of health statistics and informatics, and her colleagues, pointed to the mental health findings as particularly important. Mental health has been "mostly overlooked" in low- and middle-income countries despite the fact that "poor mental health in adolescence is associated with a high prevalence of adult emotional, behavioral, and severe psychiatric problems."

Worldwide, risk factors such as underweight, unsafe sex, alcohol use, unclean water, poor sanitation, and poor hygiene contribute most to disease burden among people aged 0-80 and older, according to the most recent WHO global disease burden study which used data from 2004.

However, the main risk factors for disability-adjusted life years in 10- to 24-year-olds – a group now representing 27% of the world’s population – were found to be alcohol use, unsafe sex (increasing the risk of disease transmission), iron deficiency, lack of contraception (leading to pregnancy), and illicit drug use, Ms. Gore and her colleagues found using data from the same study.

As in the broader global study, Ms. Gore and her colleagues used the disability-adjusted life-year (DALY), a combined measure of years of life lost due to premature death (YLL) or nonfatal disability (YLD). One DALY represents the loss of the equivalent of 1 year of full health. Ms. Gore and colleagues’ study, using data from WHO’s 2004 study, looked at DALYs by cause for 10- to 24-year-olds as a whole, broken down by geographic region, high- and low- and middle-income countries, and finally by age bracket of 10-14 years, 15-19 years, and 20-24 years. It also looked at disabilities separately from deaths.

Although leading causes of nonfatal disability among young people varied widely by geographic region, Ms. Gore and her colleagues found 10- to-24-year-olds to contribute 15.5% of the world’s total disease burden, with neuropsychiatric disorders (including alcohol-related disorders, depression, and schizophrenia) responsible for 45% of disabilities (YLDs) in this age group, according to a written statement by the authors. Accidental injuries accounted for an additional 12% of YLDs, and infectious and parasitic diseases 10% overall (although this was much higher – 22% – in Africa).

Intentional injuries, from self-inflicted injuries or violence, were a second leading cause of disability among young people in some regions, including the Americas and the eastern Mediterranean.

Ms. Gore and colleagues said in the written statement that Africa had the highest rate of DALYs for 10- to 24-year-olds, one 2.5 times greater than in high-income countries. Worldwide, DALY rates were 12% higher in girls than in boys between 15 and 19 years, a rate largely attributable, the researchers said, to maternal morbidity and mortality in Africa and Southeast Asia in that age bracket.

"Our findings suggest that one consequence of this transition is the need to increase focus on noncommunicable and nonfatal causes of disease burden both in adolescence and in later adult life. In turn, this focus is likely to shift attention to lifestyle risk factors and their social and environmental determinants," Ms. Gore and her colleagues wrote in their analysis.

The authors noted as a limitation of their study "large ranges of uncertainty for some causes and regions" in the 2004 global disease burden estimates from WHO, and added that because of these inconsistencies, small differences should not be considered important.

In an accompanying editorial, Dr. John S. Santelli and Dr. Sandro Galea of the Mailman School of Public Health at Columbia University in New York, praised the researchers for "obtaining a substantial amount of data to generate these new estimates," and called the work "important in generating data for health status by region and national income and by age of young people, and for identifying leading risk factors for incident DALYs such as alcohol and drug misuse, neuropsychiatric disorders, unsafe sex, and iron deficiency" (Lancet 2011 June 7 [doi:10.1016/S0140- 6736(11)60618-1]).

Although they cautioned that DALYs don’t tell the complete disease story in young people, the WHO study provides a strong case that targeted public health interventions, such as enforcement of seat belt laws, redesign of cars, tobacco taxes, and distribution of condoms, "are essential for reducing morbidity and mortality. Failure to act today will assuredly result in failure tomorrow," Dr. Santelli and Dr. Galea wrote.

Ms. Gore and her colleagues’ study had no outside funding, and its authors declared that they had no relevant financial disclosures. Dr. Santelli and Dr. Galea declared that they had no relevant financial disclosures.

Mental Illness Causes Most Disability in Young People Worldwide