Genetic and environmental contributions to healthcare need and utilization: a twin analysis

Health Services Research, April, 1997 by William R. True, James C. Romeis, Andrew C. Heath, Louise H. Flick, Leslee Shaw, Seth A. Eisen, Jack Goldberg, Michael J. Lyons

Sociological, economic, and social-psychological perspectives defining help-seeking and illness behavior as socially and culturally determined processes are silent on the relationship between genetic factors and seeking care, delay in seeking care, and use of health services (Mechanic 1994; Wolinsky 1988). Instead, health services utilization research has focused primarily on the relationship among demographic, social-structural, psychological, and family resources in predicting health services utilization, while largely ignoring the possibility that genetic influences may have a role as part of extant models (Marcus and Siegel 1982; Romeis, Gillespie, and Coe 1988). Reasons for this omission are beyond the scope of this article, but theoretical rationales and established familial contributions to disease and behavior suggest that genetic influences on condition status and health services utilization are likely to exist. In fact, Andersen (1995) has recently recognized the promise of investigating genetic factors as a predisposing variable in the behavior model of health services use. We believe that examining the genetic and environmental contributions to disease and treatment seeking represents a new and important line of inquiry for health services researchers. Specifically, genetic modeling may help to overcome the weakness of large residual terms common to traditional health services research by allowing for genes and common environmental influences, which typically explain a substantial amount of variance in the measurement of disease and behavior (Heath and Martin 1993; Loehlin 1992).

Genetic contributions may be considered to be of two broad types: (1) known genetic predispositional influences on the development of the disease process and (2) genetic contributions to the decision to seek care that may be mediated through personality or other constructs and affect the decision to seek care. It is plausible to investigate these contributions because genetic factors are known to influence differences in socioeconomic status (Heath et al. 1987; Taubman 1978) and personality differences (Eaves, Eysenck, and Martin 1989; Loehlin 1992), both of which influence the use of medical services. This investigation begins to examine the impact of heredity on the seeking of healthcare for four health conditions: high blood pressure, mental health, joint disorders, and hearing disorders. The genetic models we introduce in this article allow us to identify the genetic and environmental contributions to having a condition and, subsequently, to assess the varying role of heredity in seeking treatment, contingent on the presence of specific self-reported health conditions. Examining separate conditions follows the suggestions of Andersen (1995).

METHODS

The Vietnam Era Twin (VET) Registry consists of 7,375 male-male twin pairs born between 1939 and 1957, in which both members served on active military duty during the Vietnam era (May 1965-August 1975). Service may have been in Southeast Asia or elsewhere. Complete descriptions of the Registry have been previously published (Eisen et al. 1987; Eisen et al. 1989).

A 30-page mail and telephone survey of health was administered individually in 1987 to all VET Registry twins. The overall casewise response rate was 74.4 percent, and both brothers of a twin pair (i.e., pairwise) responded at a rate of 64.4 percent. Eligibility criteria for the present study are that (1) both members of the twin pair were identified from Department of Defense computer files, (2) both members of the pair completed the survey questionnaire, (3) zygosity could be successfully assigned using a questionnaire and blood group typing methodology that correctly assesses zygosity in over 95 percent of cases (Eisen et al. 1989), and (4) pairwise data were available for the pertinent variables. The final study sample contained a total of 3,602 twin pairs. Of this total, 1,789 monozygotic (MZ) and 1,483 dizygotic (DZ) twin pairs responded to all of the mental health questions, while 1,977 MZ and 1,625 DZ twin pairs responded to all of the high blood pressure, joint problem, and hearing problem questions.

Questions used for the analysis of self-reported high blood pressure, joint problems, or hearing disorders included the following items: (1) "Since 1975 or your discharge from active duty (if that was earlier), have you had any of the following health problems?" and (2) "Since 1975 or your discharge from active duty (if that was earlier), have you seen a physician for any of the following health problems?" Answers to the two questions for each of the health conditions were then recoded into a three-item scale where 0 = "do not have the condition and did not seek treatment," 1 = "have the condition but did not seek treatment," and 2 = "have the condition and did seek treatment." For the mental health measure, the question "Overall, how would you describe your adjustment to civilian life after your release from active duty?" was scored positive for the responses "considerable difficulty" or "some difficulty." The item "Have you ever consulted a healthcare professional about a mental or emotional problem?" was scored "yes" or "no." The mental health responses were compiled into a three-level mental health score in the manner parallel to that used for high blood pressure, joint disorders, and hearing disorders.