Background Both type 2 diabetes mellitus (T2DM) and hypertension aggregate in families. It is a common thought that diabetic patients with parental diabetes and/or parental hypertension are more likely to develop hypertension. This study evaluated the separate and joint effects of parental hypertension and parental diabetes on the prevalence of hypertension in patients with T2DM. Materials and methods A total of 89 956 patients from a national cohort were interviewed by telephone. Information about age, sex, onset age of diabetes, body height, body weight, systolic (SBP) and diastolic blood pressure (DBP), smoking, hypertension, and paternal and maternal history of diabetes and hypertension were obtained. Hypertension was defined in two ways: (1) a positive history; or (2) a positive history or a reported SBP >= 140 mmHg and/or DBP >= 90 mmHg in patients without a hypertension history. Results While analysed separately in logistic models, both parental diabetes and parental hypertension were positively associated with hypertension. However, when both were analysed together, only parental hypertension was positively associated with hypertension, with paternal and maternal hypertension exerting a similar effect of an approximately 2.5-fold higher risk. While considering the effect of parental hypertension, both paternal and maternal diabetes was significantly associated with a lower risk of hypertension with odds ratios of approximately 0.8. Parental hypertension was also significantly associated with increased SBP and DBP; and parental diabetes with lower values in multiple linear regression. Conclusions Parental hypertension is strongly associated with hypertension. However, parental diabetes may be protective if the effect of parental hypertension is considered.
