Nonetheless, sufficient data sets and research results exist to cautiously assess global health conditions. The first such assessment was The Global Burden of Disease (GBD) study, which began in 1992. This was the first comprehensive effort to provide comparable regional and global estimates and projections of disease and injury burden based on a common methodology and denominated in a common measure (see box).

By contrast, the established market economies and the former socialist economies of Europe, with about a fifth of the world's population, together bore less than 12 percent of the total disease burden. China emerged as the healthiest developing region, with 15 percent of the global disease burden and a fifth of the world's population. In summary, the poor in developing countries share a disproportionately large burden of ill health.

The traditional causes of disease burden in developing societies are communicable infections, maternal and perinatal conditions, and nutritional deficiencies, labeled Group I. They accounted for only 7 percent of the burden in the established market economies and less than 9 percent in the former socialist economies, but they represented more than 40 percent of the total global burden of disease in 1990 and almost half the burden (49 percent) in developing regions. In Sub-Saharan Africa, two out of three years of healthy life lost were due to these causes. Even in China, where the epidemiological transition (the transition from high prevalence of infectious diseases, primarily at younger ages, to a high prevalence and mortality from chronic diseases, especially at older ages) is far advanced, a quarter of the healthy years of life were lost. Worldwide, 5 out of 10 leading causes of disease burden (measured by DALYs) are Group I conditions: lower respiratory infections (pneumonia), diarrheal disease, perinatal conditions, tuberculosis, and measles.

The burden of injury in 1990 was highest in the former socialist economies, relative to their total disease and injury burden. China had the second-largest injury burden, followed by Latin America and the Caribbean with the third largest. Even in the established market economies, the burden of injuries--dominated by traffic accidents--was almost 12 percent of the total disease and injury burden for this group.

Six of these risk factors--malnutrition; poor water, sanitation, and hygiene; unsafe sex; alcohol; tobacco; and occupation--accounted for more than one-third of total disease burden worldwide in 1990 (see table). Malnutrition and poor sanitation were the dominant hazards, responsible for almost a quarter of the global burden.

As might be expected, major inequalities exist between regions and between men and women in the burden of most risk factors. For example, the consequences of unsafe sex--including infections and the complications of unwanted pregnancy--are borne disproportionately by women. In young adult women in Sub-Saharan Africa, unsafe sex accounts for almost one-third of the total disease burden.

The tobacco and alcohol burden was heaviest in men in the developed regions, where the two risk factors together accounted for more than one-fifth of the total burden in 1990. In Asia and other developing regions, the rapid increase in tobacco use over the past few decades is expected to kill many more people in the coming decades than so far have died in the developed regions.

Deaths from communicable infections, maternal and perinatal conditions, and nutritional deficiencies are expected to fall from 17.3 million in 1990 to 10.3 million in 2020. As a percentage of total deaths, these Group I conditions are expected to drop by more than half, from 34 percent in 1990 to 15 percent in 2020. This is due, in part, to the relative contraction of the world's young population, those under 15 years. The projection also reflects the overall decline in Group I conditions over the past four decades, due to increased income, education, and progress in developing antimicrobials and vaccines.

Deaths from noncommunicable diseases (Group II) are expected to climb from 28.1 million deaths in 1990 to almost 50 million in 2020, an increase of 77 percent in absolute numbers. In proportionate terms, the share of Group II deaths is expected to increase from 55 percent in 1990 to 73 percent in 2020.

It should not be assumed that the progress of the past four decades against infectious diseases will necessarily be maintained. Antibiotic development and other control technologies might not keep pace with the emergence of drug-resistant strains of important microbes such as Mycobacterium tuberculosis. But current evidence suggests that, as long as current efforts continue, Group I causes are likely to continue declining. The exception is HIV/AIDS global mortality, which is rising rapidly--from 300,000 deaths in 1990 to 2.7 million deaths in 1999.

For further reading see C. J. L. Murray and A. D. Lopez, The Global Burden of Disease (Cambridge, Mass., U.S.A.: Harvard University Press for the World Bank, World Health Organization, and the Harvard School of Public Health, 1996); R. Peto and A. D. Lopez, "The Future Worldwide Health Effects of Current Smoking Patterns," in Global Health in the 21st Century, ed. C. Everett Koop, C. E. Pearson, and M. R. Schway (New York: Jossey-Bass, 2000).

Alan D. Lopez (lopeza@who.ch) is coordinator of the Epidemiology and Burden of Disease Team at the World Health Organization in Switzerland.