Researchers identified an increase in the number of years lived with a disability among the global population, which they attribute to population growth and aging.
The results of the Global Burden of Disease Study 2013 (GBD 2013) were recently published in The Lancet.
Lead study author Prof. Theo Vos, of the Institute of Health Metrics and Evaluation at the University of Washington in Seattle, and colleagues set out to calculate up-to-date estimates of disease and injury incidence and prevalence among 188 countries between 1990 and 2013, using data from more than 35,000 sources.
The team also sought to estimate the number of disability-adjusted life years (DALYS) - that is, the number of healthy years lost due to illness - over the 23-year period.
In total, the researchers were able to provide global estimates of incidence and prevalence for 301 acute and chronic diseases, and they were able to assess the effects of 2,337 health consequences that result from at least one of these disorders.
Prof. Vos and colleagues found that in 2013, only 1 in 20 people (4.3%) around the globe had no health problems, meaning more than 95% of us had one or more illnesses.
The researchers found that 2.3 billion people worldwide - more than a third of us - had at least five health conditions in 2013. Over the 23-year study period, the number of people with 10 or more health conditions rose by 52%.
The number of people with multiple illnesses increased with age. In 2013, 36% of children in developed countries aged 0-4 years had no illnesses, compared with only 0.03% of adults aged 80 and older.
The number of healthy years lost due to illness increased from 21% in 1990 to 31% in 2013, and the number of years lived with disability (YLD) rose from 537.6 million in 1990 to 764.8 million in 2013.
The researchers attribute the increase in YLD over the 23-year period to population growth and aging. They found that the main drivers for YLD were musculoskeletal disorders, mental illnesses, substance abuse disorders, neurological conditions and chronic respiratory disorders.
Disability rates not declining as fast as death rates
The leading causes of health loss did not change much between 1990 and 2013, according to the researchers.
They found that in 2013, musculoskeletal disorders, such as low back pain and arthritis, and mental and substance use disorders - particularly anxiety, depression and drug and alcohol use disorders - accounted for almost 50% of all health loss globally.
Low back pain and major depression were ranked as two of the top 10 disability contributors in 2013 among every country. These conditions caused more health loss than chronic obstructive pulmonary disease (COPD), diabetes and asthma combined, according to the results.
The team found the leading causes of disability and health loss varied by regions. Falls, for example, were found to be the second leading cause of disability in 11 of 13 countries in central Europe, while anxiety disorders were more prominent causes of disability in Caribbean regions.
Past war conflict was identified as the main contributor to health loss in Cambodia, Nicaragua, Rwanda, while ranking as the second leading cause of health loss in Vietnam.
Perhaps one of the most important findings was that rates of disability as a result of health problems are not declining as rapidly as death rates from such conditions. The team points to diabetes as an example; while diabetes rates rose by 43% between 1990 and 2013, death rates from the condition only increased by 9%.
"The fact that mortality is declining faster than non-fatal disease and injury prevalence is further evidence of the importance of paying attention to the rising health loss from these leading causes of disability, and not simply focusing on reducing mortality," says Prof. Vos, adding:
"Large, preventable causes of health loss, particularly serious musculoskeletal disorders and mental and behavioral disorders, have not received the attention that they deserve. Addressing these issues will require a shift in health priorities around the world, not just to keep people alive into old age, but also to keep them healthy."
The Bill and Melinda Gates Foundation funded the study.