CHANGES IN GLUCOSE METABOLISM PLAY A ROLE IN THE ASSOCIATION BETWEEN VITAMIN D INSUFFICIENCY AND SUBCLINICAL ORGAN DAMAGE IN HYPERTENSION

Abstract

Objective: Recent studies have shown that low vitamin D levels are associated with greater subclinical target organ damage (TOD) in hypertension, but the mechanism has not been clarified. We previously reported that vitamin D (25OH-D) insufficiency is associated with a greater blood glucose response to an oral glucose load in non-diabetic patients with essential hypertension (EH). We therefore sought to investigate whether changes in glucose metabolism could play a role in the relationship between 25OH-D insufficiency and hypertensive TOD. Design and method: In 203 non-diabetic EH patients (age 50 ± 13 yr, 113 males, 85 never treated) we measured plasma levels of 25OH-D, fasting and post-glucose load (OGTT) glucose and insulin and calculated the HOMA index, and assessed renal function by measuring 24-h creatinine clearance (GFR) and urinary albumin excretion (UAE). We also performed conventional and tissue-Doppler echocardiography (TDI), carotid echo-Doppler ultrasound and renal ultrasound with measurement of intrarenal resistance indexes (IRI). Results: On univariate analysis, 25OH-D levels were inversely related with the area under the curve (G-AUC) of glucose response to OGTT (r = −0.244, P < 0.001) and also with age, left ventricular mass index (LVMI), E/A, E/e′ ratio, carotid intima-media thickness (IMT), and IRI. G-AUC was directly related with age, systolic blood pressure, body mass index, duration of hypertension, LVMI, E/A, E/e′, IMT, IRI, and inversely related to e′ velocity at TDI. Neither 25OH-D nor G-AUC were related to GFR or UAE. In multivariate models, we examined the relationship of different types of TOD that were included as dependent variables with 25OH-D levels and G-AUC that were included as independent variables together with other confounders identified in the univariate analysis. In these analyses, LVMI (B = 0.197, P = 0.008), E/A (B = −0.188, P = 0.005), and E/e′ ratio were independently related with G-AUC but not 25OH-D levels. Conversely, the IMT was independently related with 25OH-D levels (B = −0.177, P = 0.023) but not with G-AUC, and only IRI was independently related with both 25OH-D levels and G-AUC. Conclusions: These results suggest that the interaction between vitamin D and glucose metabolism might have a role in the development of subclinical organ damage in nondiabetic hypertensive patients