Background: Studies of couples, who tend to share an environment but are genetically dissimilar, can shed light on the contribution of environmental factors to hypertension. There has been renewed interest in these environmental factors following the re-analysis of the INTERSALT study.
Aim: To determine whether patients whose spouses have hypertension are at increased risk of hypertension, using a population-based case-control study.
Method: The total study population consisted of all 3923 patients over 30 years old registered with one general practice. Male cases with hypertension were matched to male controls without hypertension. Female cases with hypertension were matched to female controls without hypertension. The variables were: diagnosed hypertension; having a spouse with diagnosed hypertension; age; sex; weight; height; body-mass index; couple status; diabetes; and systolic and diastolic blood pressure readings.
Results: On multivariate analysis, when age, body-mass index, diabetes, couple status, and having a blood pressure reading were included, men whose spouses had hypertension had a two-fold increased risk of hypertension (adjusted odds ratio (OR) 2.24; 95% CI 1.77-2.72; P = 0.001). Similarly, on multivariate analysis, women whose spouses had hypertension had a two-fold increased risk of hypertension (adjusted OR = 2.23; 95% CI 1.75-2.72; P = 0.001). The risk for both male and female subjects persisted after adjustment for other variables. There was a significant correlation between systolic (r = 0.41; P < 0.0001) and diastolic (r = 0.25; P < 0.0001) blood pressures between spouse pairs.
Conclusion: The independent association between having a spouse with hypertension and increased risk of hypertension supports the view that there are significant environmental factors in the aetiology of hypertension. The finding has implications for the screening and treatment of hypertension in primary care.