Plasma 25-hydroxyvitamin d is associated with markers of the insulin resistant phenotype in nondiabetic adults

We examined the cross-sectional association between plasma 25-hydroxyvitamin D {[25(OH)D]} and markers of the insulin resistant phenotype. Plasma {25(OH)D} concentrations were measured in 808 nondiabetic participants of the Framingham Offspring Study. Outcome measures included fasting and 2-h post 75-g oral glucose tolerance test {(OGTT)} glucose and insulin; these were used to calculate the homeostatic model assessment-insulin resistance {(HOMA-IR)} and insulin sensitivity index {(ISI(0,120)).} We also measured plasma adiponectin, triacylglycerol, and {HDL} cholesterol concentrations as markers of the insulin-resistant phenotype. After adjusting for age, sex, {BMI,} waist circumference, and current smoking status, plasma {25(OH)D} concentration was inversely associated with fasting plasma glucose and insulin concentrations, and {HOMA-IR.} Compared with the participants in the lowest tertile category of plasma {25(OH)D,} those in the highest tertile category had a 1.6% lower concentration of fasting plasma glucose {(P-trend} = 0.007), 9.8% lower concentration of fasting plasma insulin {(P-trend} = 0.001), and 12.7% lower {HOMA-IR} score {(P-trend} {\textless} 0.001). After adjusting for age and sex, plasma {25(OH)D} was positively associated with {ISI(0,120),} plasma adiponectin, and {HDL} cholesterol and inversely associated with plasma triacylglycerol, but these associations were no longer significant after further adjustment for {BMI,} waist circumference, and current smoking status. {25(OH)D} and 2-h {post-OGTT} glucose were not associated. Among adults without diabetes, vitamin D status was inversely associated with surrogate fasting measures of insulin resistance. These results suggest that vitamin D status may be an important determinant for type 2 diabetes mellitus.