Association of Serum 25‐hydroxyvitamin D, Quantitative Insulin Sensitivity Check Index (QUICKI) and Homeostatic Model Assessment Indexes of Insulin Resistance (HOMA1‐IR and HOMA2‐IR) Among Three Ethnic Groups.

Objective The purpose of this study was to investigate the association between insulin sensitivity, insulin resistance and serum 25‐hydroxyvitamin D [25(OH)D] among African‐Americans (AA), Haitian‐Americans (HA) and Cuban‐Americans (CA) living in South Florida. Background Insulin sensitivity and its opposite, insulin resistance, reflect the efficacy of body in using insulin in response to elevated blood glucose. Insulin resistance/sensitivity is recognized as the major risk factor in development of type 2 diabetes. Vitamin D directly affects insulin sensitivity, Beta cell function, insulin secretion and hence mediates glucose homeostasis. Several studies reported an association between lower serum vitamin D levels and increased risk of developing type 2 diabetes. There are currently no studies investigating the relationship between serum vitamin D and insulin sensitivity/resistance among ethnic minorities. Methods This randomized cross‐sectional study included 316 participants; AA (n= 115), HA (n= 116) and CA (n= 85). Insulin sensitivity was calculated by QUICKI formula [1 / (log(fasting insulin) + log (fasting glucose)], insulin resistance was calculated by HOMA1‐IR [fasting insulin (μU/ml) × fasting glucose (mmol/L)] /22.5] and HOMA2‐IR (values were determined by an online calculator). Serum 25(OH)D and C‐reactive protein levels were measured by ELISA method. Multiple linear regression models were run, adjusting for age, gender, and C‐reactive protein. QUICKI, HOMA1‐IR and HOMA2‐IR were the dependent variables. Data analysis and results The mean age for AA, HA and CA was 50.7±8.6, 53.9±10.9 and 60.36±10.6 years respectively. The mean serum 25(OH)D for AA, HA and CA was 24.4±9.8, 21.9±6.8 and 43.2±18.8 ng/ml, respectively. In AA, Serum 25(OH)D was negatively correlated with HOMA1‐IR (r=−.179, P =.056) and HOMA2‐IR (r=−.201, P =.032). This correlation was positive and not statistically significant for 25(OH)D and QUICKI (r=.167, P =.075). Multi‐linear regression analyses controlling for the covariates indicated a significant negative association between serum 25(OH)D and HOMA1‐IR (B=−.191, P =0.042), HOMA2‐IR (B=−.213, P =0.021) but only marginally significant with QUICKI (B=.179, P =0.06) in AA. Conclusion Insulin resistance and insulin sensitivity are associated with serum vitamin D levels among AA; this association is negative for insulin resistance and positive for insulin sensitivity. HOMA2‐IR has the strongest correlation with 25(OH)D level, compared to HOMA1‐IR and QUICKI, among all 3 ethnic groups. The results of this study suggest that HOMA2‐IR may be a good predictor of vitamin D status among AA. Support or Funding Information Funding source: Funding for this research was provided through a grant from NIH/NIDDK (SC1DK083060).