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Educational Attainment and the Heritability of Self-Reported Hypertension Among Male Vietnam-Era Twins

From the Weight Control and Diabetes Research Center (J.M.M.), Brown Medical School and The Miriam Hospital, Providence, Rhode Island; Center for Statistical Sciences (G.D.P.), Brown Medical School, Providence, Rhode Island; Department of Psychology (M.J.L.), Boston University, Boston, Massachusetts; Harvard Institute of Psychiatric Epidemiology and Genetics (M.J.L.), Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts; Harvard Medical School Department of Psychiatry (M.J.L.) at Massachusetts Mental Health Center, Boston, Massachusetts; Transdisciplinary Research Group (R.N.), Butler Hospital and Brown Medical School, Providence, Rhode Island.

Address correspondence and reprint requests to Jeanne M. McCaffery, Weight Control and Diabetes Research Center, 196 Richmond Street, Providence, RI 02903. E-mail: Jeanne_McCaffery{at}brown.edu

Objective: To investigate the potential for gene x environment interaction in hypertension by examining the extent to which educational attainment modifies the heritability of hypertension in male twins. Prior twin and family studies have established that hypertension runs in families and is heritable. In addition, epidemiological research indicates that the prevalence of hypertension differs by socioeconomic factors, such as educational attainment.

Methods: Twin structural equation modeling was used to examine educational attainment as a moderator of heritability of hypertension. Participants were 4301 monozygotic and 3414 dizygotic male Vietnam-era twins who provided data on both education (in years) and self-report of physician diagnosis of hypertension or medication usage.

Results: Heritability was 17 points lower among co-twins concordant for educational attainment of 14 years (0.46, 95% CI = 0.32–0.57) relative to co-twins concordant for >14 years of education (0.63, 95% CI = 0.54–0.71). The significant moderation of the heritability (p = .04) was confirmed in twin models examining educational attainment as a continuous moderator of hypertension.

Conclusions: These results demonstrate that the expression of genetic vulnerability to hypertension can vary as a function of environmental factors, including education level, and that nongenetic pathways may differentially contribute to risk among those with fewer years of education.

Key Words: hypertension • twins • education

Abbreviations: SES = socioeconomic status; VET = Vietnam-era twin; NHANES III = Third National Health and Nutrition Survey; MZ = monozygotic; DZ = dizygotic; A = additive genetic factor; D = dominant genetic factor; C = shared environmental factor; E = nonshared environmental factor; A² = additive genetic variance; C² = shared environmental variance; E² = nonshared environmental variance; M₁ = moderator; B = linear effects of the moderator on the mean; F = quadratic effects of the moderator on the mean; T = effects of the moderator on additive genetic variance; U = effects of the moderator on shared environmental variance; V = effects of the moderator on nonshared environmental variance; NHLBI = National Heart, Lung and Blood Institute; –2lnL = twice the log likelihood.