is the impact of a health problem as measured by financial cost, mortality
, morbidity, or other indicators. It is often quantified in terms of quality-adjusted life years (QALYs) or disability-adjusted life years (DALYs), both of which quantify the number of years lost due to disease (YLDs). One DALY can be thought of as one year of healthy
life lost, and the overall disease burden can be thought of as a measure of the gap
between current health status and the ideal health status (where the individual lives to old age
free from disease and disability
). According to an article published in The Lancet
in June 2015 low back pain and major depressive disorder
were among the top ten causes of YLDs and were the cause of more health loss than diabetes, chronic obstructive pulmonary disease, and asthma combined. The study based on data from 188 countries, considered to be the largest and most detailed analysis to quantify levels, patterns, and trends in ill health and disability, concluded
that "the proportion of disability-adjusted life years due to YLDs increased globally from 21.1% in 1990 to 31.2% in 2013." The environmental burden of disease
is defined as the number of DALYs that can be attributed to environmental factors
. These measures allow for comparison of disease burdens, and have also been used to forecast the possible impacts of health interventions. By 2014 DALYs per head were "40% higher in low-income and middle-income regions."
The World Health Organization (WHO) has provided a set of detailed guidelines for measuring disease burden at the local or national level. In 2004, the health issue leading to the highest YLD for both men and women was unipolar depression
; in 2010, it was lower back pain. According to an article in The Lancet published in November 2014, disorders in those aged
60 years and older represent "23% of the total global burden of disease" and leading contributors to disease burden in this group in 2014 were "cardiovascular diseases (30.3%), malignant neoplasms (15.1%), chronic respiratory diseases (9.5%), musculoskeletal diseases (7.5%), and neurological and mental disorders (6.6%)."