Association Between Vitamin D and Glycaemic Parameters in a Multi-Ethnic Cohort of Postmenopausal Women with Type-2 Diabetes in Saudi Arabia
Abstract Background: The relationship between Vitamin D (VitD) with insulin sensitivity and secretion in Type-2 diabetes (T2D) has shown to be different amongst different ethnic populations. In Saudi Arabia, where both T2D and VitD deficiency are highly prevalent health concerns, little is known about the relationship between VitD, insulin sensitivity, resistance and the relative importance of ethnicity. Our aim in this study is to investigate influence of ethnicity on VitD association with glycaemic profile primarily and to measures of obesity secondarily, among multiethnic postmenopausal women with T2DM in Saudi Arabia.Methods: A cross-sectional study was conducted at King Fahad Medical Research Center, King Abdulaziz University, Jeddah, Saudi Arabia. Postmenopausal females (n = 173, age ≥ 50 years) with T2D were randomly selected in this study. Anthropometric measures and fasting blood samples were obtained for all study participants. Several biochemical parameters were measured including 25-hydroxyvitamin D (25(OH)D), glycosylated hemoglobin (HbA1c), insulin, glucose and c-peptide. Surrogate markers for insulin resistance were calculated using Homeostasis Model Assessment 2 for insulin resistance and beta cell activity (HOMA2-IR, HOMA2-β).Results: Overall, 25(OH)D was inversely associated with fasting glucose (r=-0.165, P=0.037), insulin (r=-0.184, P=0.02), C-peptide (r=-0.19, P=0.015) and HOMA2- IR C-peptide (r=-0.23,P=0.004). Additionally, serum 25 (OH)D showed an overall a negative correlation with body weight (r=-0.173 P=0.028), waist and hip circumferences (r=-0.167, P=0.033; r=-0.22, P=0.004 respectively) but not with body mass index (BMI) or waist hip ration (WHR). In the white ethnic group but not in black or Asian population groups, 25(OH)D level was associated with only serum fasting C-peptide and HOMA2-IR C-peptide and BMI (P<0.05). Conclusions: Insulin resistance and obesity are associated with VitD status in T2D in this cohort. Our findings also suggest that these VitD associations in women from white ethnic background are different than in those from black/Asian ethnic backgrounds. Whether VitD supplements are able to improve degree of obesity and insulin sensitivity should be further investigated in different ethnic population groups.