Abstract
Recent evidence indicates that mildly increased fasting and post-oral load blood glucose concentrations contribute to development of organ damage in nondiabetic patients with hypertension. In previous studies, vitamin D deficiency was associated with decreased glucose tolerance. The aim of this study was to examine the relationships between serum 25(OH)D levels and glucose tolerance and insulin sensitivity in hypertension. In 187 nondiabetic essential hypertensive patients free of cardiovascular or renal complications, we measured serum 25-hydroxyvitamin D (25(OH)D) and parathyroid hormone (PTH) and performed a standard oral glucose tolerance test (OGTT). Patients with 25(OH)D deficiency/insufficiency were older and had significantly higher blood pressure, fasting and post-OGTT (G-AUC) glucose levels, post-OGTT insulin (I-AUC), PTH levels, and prevalence of metabolic syndrome than patients with normal serum 25(OH)D. 25(OH)D levels were inversely correlated with age, blood pressure, fasting glucose, G-AUC, triglycerides, and serum calcium and PTH, while no significant relationships were found with body mass index (BMI), fasting insulin, I-AUC, HOMA index, and renal function. In a multivariate regression model, greater G-AUC was associated with lower 25(OH)D levels independently of BMI and seasonal vitamin D variations. Thus, in nondiabetic hypertensive patients, 25(OH)D deficiency/insufficiency could contribute to impaired glucose tolerance without directly affecting insulin sensitivity.
Highlights
Type 2 diabetes mellitus, impaired fasting glucose, and the associated insulin resistance are well known risk factors for cardiovascular diseases both in the general population and hypertensive patients [1,2]
No differences among groups were found in sex, body mass index (BMI), duration of hypertension, use of antihypertensive drugs, renal function, fasting plasma insulin and C-peptide, homeostatic model assessment (HOMA) index, plasma levels of cholesterol, triglycerides, and serum calcium and magnesium
Serum 25(OH)D levels are inversely and independently correlated with post-load blood glucose concentration, but not with fasting and post-load insulin levels or the HOMA index. These findings suggest that in nondiabetic hypertensive patients, low vitamin D levels could contribute to impaired glucose tolerance without directly affecting insulin sensitivity
Summary
Type 2 diabetes mellitus, impaired fasting glucose, and the associated insulin resistance are well known risk factors for cardiovascular diseases both in the general population and hypertensive patients [1,2]. Due to the possible relevance of blood glucose spikes even in normoglycemic subjects, timely identification of factors that might impair glucose metabolism in nondiabetic hypertensive patients could be important for the prevention or reversal of cardiovascular damage. In addition to the well-known conditions that predispose to glycometabolic changes such as ethnicity, family history of diabetes, overweight-obesity, inappropriate diets, and physical inactivity, new factors have been recently called into play as possible contributors to glucose metabolism impairment. These factors include inflammatory states [7], circulating levels of adipocytokines [8], the host-microbiota composition [9], and the vitamin D status [10]. An inverse relationship between serum 25(OH)D levels and both fasting and 2-h blood glucose after an oral glucose load was reported in predominantly vitamin D-deficient overweight/obese subjects [11], supporting the hypothesis of an association between vitamin D deficiency and decreased glucose tolerance
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