Low circulating vitamin D levels are associated with increased arterial stiffness in prediabetic subjects identified according to HbA1c.

Background and Aims: We investigated serum -hydroxyvitamin D levels [25(OH)D] and their correlation with early markers of cardiovascular disease in subjects with pre-diabetes. We particularly focused on individuals identified only by glycated hemoglobin A1c (HbA1c 5.7-6.4%) according to the American Diabetes Association criteria but who were normotolerant (NT) after oral glucose tolerance test (OGTT) and had normal fasting glucose (NFG).
Methods: 25(OH)D levels, HbA1c, OGTT, arterial stiffness and intima-media thickness (IMT) were evaluated in 286 subjects without history of diabetes. Subjects were stratified into four groups: controls with HbA1c <5.7%, NFG and NT; prediabetic patients with pre-diabetes according to only HbA1c (HbA1c 5.7-6.4% and NFG/NT); subjects with impaired fasting glucose and impaired glucose tolerance (IFG/IGT); new onset type 2 diabetes (HbA1c ≥ 6.5%).
Results: Subjects with NFG/NT and HbA1c 5.7-6.4% (n = 83) showed lower 25(OH)D levels compared with controls (n = 80) (21.7 [15.8-31.1] vs 23.1 [17.1-29.7] ng/mL, P = 0.009); these values were similar to those of the IFG/IGT group and were higher but not significantly different from subjects with new onset type 2 diabetes. After multiple regression analyses, only HbA1c and BMI were independently associated with 25(OH)D levels. Age, HbA1c and 25(OH)D were the major determinants of Augmentation Index. No independent association between 25(OH)D and IMT was found.
Conclusions: Subjects with pre-diabetes (HbA1c 5.7-6.4% and NFG/NT) had significantly reduced 25(OH)D levels compared with controls. Reduction of 25(OH)D levels is inversely associated with arterial stiffness independently of classical risk factors and inflammatory markers. Based on these data, subjects with NFG and NT are not a homogeneous population of patients, and they present different cardiovascular and glycometabolic risks. Our data suggest considering HbA1c as a reliable marker of cardiovascular and metabolic risk independent of fasting and post-load glycemia.
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