The heritability of blood pressure: an investigation of 200 pairs of twins using the cold pressor test.

Blood pressures in 200 pairs of twins having a mean age of 14.0 (S.D. equals 6.5) years were measured at basal levels and in response to the cold pressor test. Intraclass correlations were consistently larger (and intrapair variances consistently smaller) in monozygotic as compared to dizygotic pairs, substantially more so in females than in males. Sex differences in heritability were somewhate greater for systolic than for diastolic blood pressure. Indices of heritability (H) at basal levels were, in descending order: 0.78 (female systolic), 0.61 (female diastolic), 0.56 (male diastolic), and 0.41 (male systolic). The same descending order for H was found for blood pressure responses to the cold pressor test. It is concluded that in the population studied, genetic factors play an important role in the control of blood pressure over the normal range of vascular reactivity. In females, such factors may be the major determinant of the variability observed.