the environment and certain genes leads to diseases like asthma. The National Institute of Allergy and Infectious Diseases (NIAID) and NIEHS are extending the Inner City Asthma Study, a study of children with asthma in seven U.S. cities that is examining the effects of interventions to reduce children's exposure to indoor allergens and improve communication with their primary care physicians. This investigation also involves collaboration with the Environmental Protection Agency to evaluate the effects of exposure to indoor and outdoor pollutants. Integrating findings from these studies into a unified multilevel explanation of how asthma comes about, together with an assessment of preventive and curative interventions is an important future priority that will require integrative analyses of the sort described throughout this report.

HEALTH AND THE MACROECONOMY

The health status of the population may have macroeconomic effects in addition to affecting individual behavior. Empirically, countries that are less healthy are poorer than countries that are more healthy, and their incomes grow less rapidly. Thus, the income gap between more and less healthy countries is increasing over time. Recent research indicates that life expectancy is a powerful predictor of national income levels and subsequent economic growth (Fogel, 1999). Studies consistently find a strong effect of health on growth rates. Economic historians have concluded that perhaps 30 percent of the estimated per capita growth rate in Britain between 1780 and 1979 was a result of improvements in health and nutritional status (Fogel and Costa, 1997). That lies within the range of estimates produced by cross-country studies using data from the last 30-40 years (Jamison et al., 1998).

Health improvements also influence economic growth through their impact on demography. For example, in the 1940s rapid health improvements in East Asia provided a catalyst for demographic transition. An initial decline in infant and child mortality first dramatically increased the number of young people and then somewhat later prompted a fall in fertility rates. These asynchronous changes in mortality and fertility, which comprise the first phase of what is called the “demographic transition,” substantially altered East Asia's age distribution. After a time lag the working-age population began growing much faster than young dependents, temporarily creating a disproportionately high percentage of working-age adults. This bulge in the age structure of the population created an opportunity for increased economic growth (Bloom, 1999).

Over the past several years, the Pan American Health Organization/Inter-American Development Bank and the United Nations Economic Commission for Latin America and the Caribbean carried out a study to eluci-



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