Genetic and environmental influences on blood pressure in elderly twins.

We used 289 pairs of Swedish twins reared apart or together to evaluate the importance of genetic and environmental influences on blood pressure. Unlike other twin and family studies, the adoption/twin design allows a distinction between estimates of the importance of shared rearing environments and genetic effects. Genetic factors were observed to play an important role for individual differences in blood pressure. Model-fitting analyses suggested upper limits of heritability for systolic and diastolic blood pressures in the entire sample of 0.44 and 0.34, respectively. More interestingly, substantial influences of shared family effects accounting for up to 27% of the variation were also revealed. Effects of correlated environment, which might reflect, for example, the intrauterine environment, existed to some extent later in life. The influence of genetic factors tended to decrease across age groups for systolic blood pressure (0.62 in individuals less than 65 years old; 0.12 in those 65 years and older) but not for diastolic blood pressure (0.22 for the middle-aged group; 0.26 for the older group). However, this declining trend for systolic blood pressure did not reach significance (chi 2 = 8.07, df = 4, P = .09).