Type 2 Diabetes and Hypertension A Study on Bidirectional Causality

Rationale: In observational studies, type 2 diabetes mellitus (T2D) has been associated with an increased risk of hypertension, and vice versa; however, the causality between these conditions remains to be determined. Objectives: This population-based prospective cohort study sought to investigate the bidirectional causal relations of T2D with hypertension, systolic and diastolic blood pressure (BP) using Mendelian randomization (MR) analysis. Methods and Results: After exclusion of participants free of a history of heart failure, cardiovascular disease, cardiac procedures, and non-T2D diabetes mellitus, a total of 318 664 unrelated individuals with qualified genotyping data of European descent aged 37 to 73 from UK Biobank were included. The genetically instrumented T2D and hypertension were constructed using 134 and 233 single nucleotide polymorphisms, respectively. Seven complementary MR methods were applied, including inverse-variance weighted method, 2 median-based methods (simple and weighted), MR-Egger, MR-robust adjusted profile scores, MR-Pleiotropy Residual Sum and Outlier, and multivariate MR. The genetically instrumented T2D was associated with risk of hypertension (odds ratio, 1.07 [95% CI, 1.04-1.10], P=3.4x10(-7)), whereas the genetically determined hypertension showed no relationship with T2D (odds ratio, 0.96 [0.88-1.04], P=0.34). Our MR estimates from T2D to BP showed that the genetically instrumented T2D was associated with a 0.67 mm Hg higher systolic BP (95% CI, 0.41-0.93, P=5.75x10-7) but not with a higher diastolic BP. There was no clear evidence showing a causal effect of elevated systolic BP or diastolic BP on T2D risk. Positive pleiotropic bias was indicated in the hypertension. T2D relation (odds ratio, of MREgger intercept 1.010 [1.004-1.016], P=0.001) but not from T2D to hypertension (1.001 [0.998-1.004], P=0.556). Conclusions: T2D may causally affect hypertension, whereas the relationship from hypertension to T2D is unlikely to be causal. These findings suggest the importance of keeping an optimal glycemic profile in general populations, and BP screening and monitoring, especially systolic BP, in patients with T2D.