(CNN) -- As the world's population continues to rise, more children are surviving into adulthood, a new study finds, but rates of disability have increased as well.
Research published Monday in the journal JAMA Pediatrics found that from 1990 to 2017, global child and adolescent deaths decreased 51.7%, while disability increased 4.7%. Additionally, there is a growing gap between young people's health outcomes between different countries.
The study was part of the Global Burden of Disease report. In 2017, the most common killers of children and adolescents were diarrhea, acute malnutrition and lower respiratory tract infections. However, deaths among children and adolescents fell from 13.77 million in 1990 to 6.64 million in 2017.
Among countries with higher socioeconomic development, some of the main contributors to disability were birth defects, neonatal disorders, headache, dermatitis and anxiety. In lower-development countries, lower respiratory infections, diarrhea and malaria, as well as birth defects and neonatal disorders contributed to disability.
When researchers looked at death and disability in people up to age 19 in 195 territories and countries, they found that the regions with the greatest decline in childhood deaths were Central, Eastern and sub-Saharan Africa, while the fastest rates of decreased death were in Andean Latin America, South Asia and East Asia. The authors attribute these improvements to practices such as more widespread vaccinations, improved sanitation and nutrition, and targeting of malaria and sexually transmitted infections.
In sub-Saharan Africa, reduced mortality due to tropical diseases, infections and nutritional deficiencies resulted in healthier children from 1990 to 2017, but other public health issues remain. "While malaria has decreased dramatically across the African continent, there are many countries, especially in sub-Saharan Africa, where parasite transmission, acute illness, and mortality from malaria remain high," the researchers noted.
There was also a 0.6% increased risk of young people dying of HIV/AIDS or sexually transmitted infections from 1990 to 2017 in southern sub-Saharan Africa. Fifty countries showed an increased risk of death due to self-harm or interpersonal violence.
The researchers also found that the greatest decrease in death was in children ages 1 to 4 -- by 61% -- while adolescents, ages 10 to 19, saw the slowest improvements.
A mother's well-being can contribute to a child's health, they noted. Countries where maternal deaths were reduced also decreased child and adolescent deaths. Poor health outcomes are more likely when there is decreased funding into education and family planning, the researchers said, and so officials should make the health of young women a priority.
The authors say that in countries with low and middle socioeconomic development, the growing number of children surviving with health problems will strain already-burdened health and educational systems. "The cost of sustaining progress on child and adolescent health and well-being is not insignificant."
The authors noted some limitations of their research, such as the results being influenced by availability of data. Some of the data may be outdated or imprecise because of lags in data reporting or in conflict zones, such as Afghanistan, Syria and Iraq.
As more children survive into adulthood, countries will have to meet the individual needs of their youngest citizens, the researchers say. "All countries must make strategic investments in education and health systems, including human resources for health, supply chains, infrastructure, governance, and increased support for children with developmental disabilities."
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