Clinical utility of serum 25-hydroxyvitamin D in the diagnosis of insulin resistance and estimation of optimal 25-hydroxyvitamin D in U.S. adults.

AIMS

To assess the clinical utility of measuring serum 25-hydroxyvitamin-D [25(OH)D] along with traditional risk factors in the diagnosis of insulin resistance (IR) and to estimate the optimal 25(OH)D level associated with normal glucose and insulin homeostasis.

METHODS

A cross-sectional analysis of 6868 adults aged≥20years without diagnosed diabetes in the National Health and Nutrition Examination Survey, with available standardized 25(OH)D data (2001-2010). IR was defined by the homeostatic-model-assessment of insulin resistance (HOMA-IR; ≥75th percentile, sex-specific: 3.9 in men or 3.6 in women). Using logistic regression, two risk models were developed to estimate the risk of IR: Model 1 included established risk factors, and Model 2 additionally included serum 25(OH)D. Predictiveness curves and decision-curve analysis were used to assess differences in IR detection among models. Receiver-operating-characteristic curves were used to estimate the lower threshold for 25(OH)D. Results were validated in a testing sample.

RESULTS

Model 2 marginally improved detection of IR: at a risk threshold of 0.2, adding 25(OH)D would identify an additional 2 to 4 cases per 1000 people. Overall, the lower 25(OH)D threshold was estimated at 60nmol/L, however, the threshold differed by ethnicity (Mexican-Americans: 54nmo/L, non-Hispanic whites: 68nmol/L, and non-Hispanic blacks: 41nmol/L).

CONCLUSION

Addition of serum 25(OH)D to traditional risk factors provided small incremental improvement in detection of IR in asymptomatic adults. The optimal 25(OH)D threshold was estimated to be at least 60nmol/L, however, the threshold may differ by ethnic-background. Further research is needed to validate these results in other populations.