Burden of Disease Attributable to Individual Risk Factors
Detailed results by risk factor, disease outcome, age, sex, and region are provided in annex 4A. Figure 4.1 shows the contributions of the leading global risk factors to all-cause mortality and burden of disease. The different ordering of risk factors in their contributions to mortality and to the disease burden expressed in DALYs reflects the age profile of mortality, such as the higher contribution to the disease burden from mortality among children as a result of underweight, and of nonfatal outcomes, such as neuropsychiatric diseases caused by alcohol use.
[Figure
4.1]
The leading causes of mortality and the disease burden include risk factors for communicable, maternal, perinatal, and nutritional conditions (Group I as defined in chapter 3), such as undernutrition; indoor smoke from household use of solid fuels; unsafe water, sanitation, and hygiene, whose burden is primarily concentrated in low-income regions of South Asia and Sub-Saharan Africa; and unsafe sex. They also include risk factors for noncommunicable diseases and injuries (Groups II and III as defined in chapter 3), such as high blood pressure and cholesterol, smoking, alcohol use, and overweight and obesity, which affect most regions.
Undernutrition is the single leading global cause of health loss, as it was in 1990 (the 2001 results disaggregate undernutrition into underweight and micronutrient deficiencies). Even though the prevalence of underweight has decreased in most regions in the past decade, it has increased in Sub-Saharan Africa (de Onis, Frongilla, and Blossner 2000; de Onis and others 2004), where its effects are disproportionately large because of simultaneous exposure to other risk factors for childhood disease. Three-quarters of the burden of disease attributable to unsafe sex is also in Sub-Saharan Africa, primarily as a result of HIV/AIDS, followed by South Asia (13 percent). The burden of disease attributable to unsafe water, sanitation, and hygiene has declined since 1990, mostly because of a worldwide decline in mortality from diarrheal disease, which is partly a result of improved case management interventions, particularly oral rehydration therapy. The increase in the global burden of disease attributable to smoking since 1990 mostly reflects the increased accumulated hazards of this risk, which is most noticeable in developing countries, but the increase is also partially due to methodological changes based on new evidence on the magnitude of the hazard after correction for confounding (Ezzati, Henley, Lopez, and others 2005; Ezzati, Henley, Thun, and others 2005; Ezzati and Lopez 2003; Thun, Apicella, and Henley 2000). The large increase in the burden of disease due to high blood pressure is likely to be an outcome of major methodological improvements, that is, relative risks that account for regression dilution bias and choice of theoretical-minimum-risk exposure distribution based on epidemiological evidence versus clinical definitions.
Table 4.2 shows the distributions of mortality and the disease burden attributable to the risk factors by age and sex. The disease burden attributable to underweight and micronutrient deficiencies in children was equally distributed among males and females, but the total all-age disease burden from iron and vitamin A deficiencies was slightly greater among females because of the effects on maternal mortality and morbidity conditions. Other diet-related risks, physical inactivity, environmental risks, and unsafe sex contributed almost equally to the disease burden in males and females. Approximately 77 to 86 percent of the disease burden from addictive substances occured among men, reflecting the social and economic forces that have so far made addictive substances more widely used by men, especially in developing countries. Women suffered an estimated two-thirds of the disease burden from child sexual abuse and all of the burden caused by non-use and use of ineffective methods of contraception.
[Table .]
The estimated disease burdens from childhood undernutrition and unsafe water, sanitation, and hygiene were almost exclusively among children under five years of age. For these risks, more than 90 percent of the total attributable burden occurred in this age group, with the exception of iron deficiency, where adults bore more than 40 percent of burden, especially women of childbearing age. The disease burdens attributable to overweight and obesity and smoking were almost equally distributed among adults below and above the age of 60 years. The disease burdens attributable to other diet-related risks and physical inactivity were higher among those older than 60 (see also chapter 5).
More than 90 percent of the disease burden attributable to non-use and use of ineffective methods of contraception, illicit drug use, and child sexual abuse and more than 75 percent of the disease burden attributable to alcohol use and unsafe sex occurred in adults younger than 60. Most of the risks whose burden is concentrated among younger adults are those with outcomes that include HIV/AIDS, maternal conditions, neuropsychiatric diseases, and injuries. This illustrates the large, and at times neglected, disease burden from risks that affect young adults, especially in low-and-middle-income countries, with important consequences for economic development.
Only a small fraction of the disease burden from the risk factors considered was among those aged 5 to 14 years. This was because some of the leading conditions that affect this age group, such as motor vehicle accidents and other injuries and depression, have complex and heterogeneous causes that could not easily be included in the risk-based framework used. For other leading diseases of this group, such as diarrhea and lower respiratory infections, most epidemiological studies have focused on children younger than five and do not provide estimates of hazardous effects for older children.
Figure 4.2 presents the burden of disease due to the 10 leading risk factors for low- and middle-income countries and for high-income countries by disease or disease group. Leading causes of the burden of disease in low- and middle-income countries include the risk factors affecting the poor and associated with communicable, maternal, perinatal, and nutritional conditions (Group I)—such as childhood underweight (8.7 percent); unsafe water, sanitation, and hygiene (3.7 percent); indoor smoke from household use of solid fuels (3.0 percent); and unsafe sex (5.8 percent)—along with risk factors for noncommunicable diseases (Group II), including addictive substances, nutrition related risks, and physical inactivity.
[Figure
4.2]
The relative contribution of unsafe sex was disproportionately larger in Sub-Saharan Africa (17.8 percent) than in all other regions, because HIV/AIDS prevalence and mortality are higher in Sub-Saharan Africa than anywhere else. This makes unsafe sex a leading cause of the burden of disease in this region together with childhood underweight (17.1 percent). The outcomes of these two risk factors were mostly communicable, maternal, perinatal, and nutritional conditions, which dominate the disease burden in high-mortality developing regions.
In addition to their relative magnitude, the absolute loss of healthy life years attributed to risk factors in low- and middle-income regions is enormous. In these regions, which account for 85 percent of the global population, childhood underweight and unsafe sex alone contributed more to the loss of healthy life (200 million DALYs[3,0]) than all diseases and injuries in high-income countries (149 million DALYs[3,0]). In high-income countries, smoking (12.9 percent), high blood pressure (9.3 percent), overweight and obesity (7.2 percent), high cholesterol (6.3 percent), and alcohol use (4.4 percent) were the leading causes of loss of healthy life, contributing mainly to noncommunicable diseases and injuries (groups II and III).
