A Disability Adjusted Life Year (DALY) is a measure of burden of disease that takes into account years of life lost due to premature death as well as years of productive life lost to poor health or disability. For a given population, DALYs are calculated by summing the Years of Life Lost (YLL) prematurely and the Years Lived with Disability (YLD, which are weighted). Improvements in the U.S.’s age-standardized disease burden (DALY) rate since 1990 have largely come from improvements in premature death (years of life lost), as opposed to improvements in the years lived with disability.
Though DALYs have declined in the U.S. and comparable countries since 2000, the U.S. continues to have higher age-adjusted rates of years of life lost to disability and premature death than comparable countries.
Since 1990, the age-adjusted burden of disease (DALY) rate has dropped by 14%, while comparable countries have seen an average decrease of 18% (ranging from a 15% decline in Canada to a 23% drop in Germany).
In the U.S. in 2013, the leading causes of death were circulatory diseases and cancers. When analyzing health outcomes, we often look at mortality rates. However, as a measure of the health of the population, mortality statistics only tell us about diseases that can lead to death and do not show the burden of disease that arises from disabilities that may not ultimately cause death. Mortality rates also do not account for age at the time of death.
When the burden of disease is defined more broadly to include disability as well as mortality, mental health and substance use disorders emerge as the leading causes of DALYs in the U.S., in addition to circulatory conditions and cancer.
In the U.S. in 2013, the leading causes of years lived with disability (YLD) were mental health conditions, musculoskeletal disorders, and endocrine disorders (including diabetes). This represents one part of the DALY calculation, and is a product of the number of cases of illnesses and the duration of the illness before it resolves or leads to death. YLDs account for the severity of the disability, and are typically weighted so that young adult ages are valued higher than infants or the very elderly.
The leading causes of years of life lost (YLL) in the U.S. are cancers, circulatory conditions, and injuries. In addition to years lived with disability (YLD), the calculation of DALYs also involves calculating years of life lost (YLL), a measure of premature death. YLL is a product of the number of deaths and life expectancy at age of death.
Over time, the diseases that cause the most DALYs in the U.S. have changed. In 1990, circulatory illnesses were the leading cause, but have since declined significantly, particularly driven by a reduction in the years of life lost from coronary heart disease (which includes angina and heart attack). DALYs caused by injuries – particularly from car accidents – have also decreased significantly since 1990, as have DALYs from cancers.
For each of the disease categories with improvements in age-standardized DALYs, the improvement has come primarily from a reduction in the years of life lost (as opposed to a reduction in the year lived with disability).
Although not a leading cause of DALYs in the U.S. (and not shown in the chart above), there has also been a significant decrease in the number of DALYs resulting from HIV/AIDS since 1990.
Since 1990, the age-adjusted burden of disease (DALY) rate caused by circulatory conditions has dropped by 36% in the U.S., while the rate in comparable countries has dropped by 47% on average. Circulatory diseases are the leading cause of death and the second-leading cause of DALYs in the U.S., so improvements in these conditions can have a significant effect on the overall disease burden and death rates. However, the U.S. saw the slowest improvement of any comparable country relative to 1990, and as of 2013 has the highest rate of disease burden caused by circulatory conditions among these countries.
Disease burden rates caused by cancer, though, have dropped at similar rates in the U.S. (down 19%) relative to other comparable countries (which ranged from a decrease of 13% in Sweden to a decrease of 27% in Germany).
For males, disease burden most caused by circulatory diseases; for females, mental health is leading cause
Although mental health and substance abuse conditions are a leading contributor to DALYs for both sexes, males have higher rates of disease burden caused by circulatory diseases, cancers and tumors, and injuries.