Discussion
Despite inherent uncertainties in population health risk assessment, described in chapter 5 and in chapters devoted to individual risk factors elsewhere (Ezzati and others 2004), the quantification of the burden of disease attributable to the individual and joint hazards of selected risk factors illustrates that those risk factors that affect the poorest regions and populations, such as undernutrition; unsafe water, sanitation, and hygiene; and indoor smoke from household use of solid fuels, continue to dominate the loss of health worldwide. These are coupled with hazards such as alcohol use, smoking, high blood pressure, high cholesterol, and overweight and obesity that are globally widespread and have large health effects.
The large remaining burden due to childhood mortality risks such as undernutrition; unsafe water, sanitation, and hygiene; and indoor smoke from household use of solid fuels indicates the persistent need for developing and delivering effective interventions, including lowering the costs of pertinent technological interventions. At the same time, four of the five leading causes of lost healthy life affect adults: high blood pressure, unsafe sex, smoking, and alcohol use (figure 4.1). Risk factors for both adult communicable and noncommunicable diseases already make substantial contributions to the disease burden even in regions with low income and high infant mortality. Therefore, the public health community should continually reassess the need for interventions addressing both childhood disease risk factors and those that affect adult health. Dynamic and systematic policy responses can, to a large extent, mitigate the spread of such risk factors and their more distal causes throughout the development process, for example, through cleaner environmental or healthier nutritional transitions (Arrow and others 1995; Lee, Popkin, and Kim 2000). In addition, as illustrated by the persistence of diseases such as malaria or the large increase in the disease burden due to HIV/AIDS and its risk factors since 1990, as well as the potential for generalized HIV/AIDS epidemics in some Eastern European countries (MacLehose, McKee, and Weinberg 2002) and China (Kaufman and Jing 2002), risk factors for important communicable diseases also require dynamic monitoring and policy responses.
Risk factors that were not among the leading global causes of the disease burden should not be neglected for a number of reasons. First, the analysis could be expanded with other risk factors that are both prevalent and hazardous. Second, although smaller than other risk factors, many make non-negligible contributions to the burden of disease in various populations. For example, in the low- and middle-income countries of East Asia and the Pacific, which is dominated by China in terms of population, urban air pollution from transportation and industrial and household energy use based on coal has health effects comparable to those of micronutrient deficiencies. Similarly, non-use and use of ineffective methods of contraception was associated with a larger disease burden than most chronic disease risk factors among females in South Asia and Sub-Saharan Africa. Third, for other risk factors, such as child sexual abuse, ethical considerations may outweigh direct contributions to the disease burden in policy debate. Finally, while the burden of disease due to a risk factor may be comparatively small, effective or cost-effective interventions may be known. Examples include reducing the number of unnecessary injections at health facilities coupled with the use of sterile syringes and the reduction in exposure to urban air pollution in industrial countries in the second half of the 20th century, which often also led to benefits such as energy savings.
A small number of risks account for large contributions to the global loss of healthy life. Furthermore, several are relatively prominent in regions at all stages of development. While reducing all the risks discussed to their theoretical minimums may not be possible using current interventions, the results illustrate that preventing disease by addressing known distal and proximal risk factors can provide substantial and underutilized public health gains. Treating established disease will always have a role in public health, especially in the case of diseases such as tuberculosis, where treatment contributes to prevention. At the same time, the current devotion of a disproportionately small share of resources to prevention by reducing major known risk factors through personal and nonpersonal interventions should be reconsidered in a more systematic way in light of the evidence presented here.
The estimates of the joint contributions of 19 selected global risk factors showed that these risks together contributed to a considerable loss of healthy life in different regions of the world. In particular, for some of the leading global diseases, such as lower respiratory infections, diarrhea, HIV/AIDS, lung cancer, ischemic heart disease, and stroke, substantial proportions were attributable to these selected risk factors. This concentration of the disease burden further emphasizes the contribution of leading risks such as undernutrition, unsafe sex, high blood pressure, and smoking and alcohol use to the loss of healthy life globally. The results further emphasize that for more effective and affordable implementation of a prevention paradigm, policies, programs, and scientific research should acknowledge and take advantage of the interactive and correlated role of major risks to health, across and within causality layers.
