forces the interrelatedness of many factors. Health outcomes are the product of complex interactions of factors rather than of individual factors operating in isolation. Indeed, these interactions are probably as important as the actions of any single factor. Currently incomplete, however, are descriptions of mechanisms underlying the linkages among the various determinants and full characterizations of the interactions among factors. The committee encourages the continued research needed to gain a better understanding of these mechanisms.

Second, not all of the determinants, viewed as causes, act simultaneously. The effects of some determinants, in fact, may be necessary antecedents to others, and some may have their primary influence by modifying the effects of others. Some may also differ in their relationship to health according to when they are present in the life cycle. Evidence suggests that there are certain times in the human life cycle that are critical for future health and well-being. During infancy and early childhood, crucial neurologic, cognitive, and psychosocial patterns are established (Carnegie Task Force on Meeting the Needs of Young Children, 1994; Entwisle, 1995). Experiences in childhood and adolescence may also have a critical influence on adult health risk factors such as weight and smoking (Dietz, 1994; IOM, 1994).

Another Perspective

Patrick and Wickizer (1995) have extended the field model framework by focusing on factors in the social and physical environments that operate at the community rather than the individual level. These two components are seen as affected by cultural, political, policy, and economic systems. In turn, they influence elements such as community response, activation, and social support, and ultimately community outcomes including social behaviors, community health, and quality of life. For example, establishing a smoke-free workplace policy exerts an influence on exposure to tobacco smoke separate from the smoking practices of individuals. This perspective points both to the influence of community-level factors and to the opportunities for community-level interventions.

INTERVENTIONS TO IMPROVE HEALTH

Many factors can influence the impact of interventions to improve health. It is possible to target various determinants of health



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