oa Vitamin D Deficiency and the Risk of Metabolic Syndrome within the Qatar Biobank: A Cross-Sectional Study

Background

Despite the long hours of sunlight in Qatar and other regions of the Middle East, vitamin D deficiency ( < 20 ng/mL) has been rising. There are many factors that affect the synthesis of vitamin D including age, ethnicity, skin pigmentation, anthropometric measures, diet, smoking, physical activity, cholesterol levels, and sunscreen usage. In parallel, the prevalence of obesity and metabolic syndrome has also been increasing in Qatar. Vitamin D deficiency has been associated with adiposity and metabolic syndrome but data are inconsistent. Individual factors of metabolic syndrome including abdominal obesity, lipid profiles, blood glucose, and blood pressure have also shown inconsistent associations with low vitamin D levels. To date, none of these relationships have been explored in a Middle Eastern population characterised by high prevalence of obesity and metabolic syndrome. Objectives The aim of this study is to investigate the interrelationship of anthropometric measures (height, waist circumference, waist-to-hip ratio, body mass index (BMI), and weight), metabolic syndrome, metabolic factors, and vitamin D in the Qatar Biobank. Methods A cross-sectional study of 1,205 participants (702 women and 503 men) from the Qatar Biobank comprising Qataris and non-Qataris (residents of greater than 15 years), was used to perform multivariate logistic regression analyses for anthropometric measures and vitamin D deficiency. The relationship between vitamin D and the risk of metabolic syndrome, metabolic factors and diabetes were also investigated. Odds ratios (OR), 95% confidence intervals (CI) and p-values were calculated for all analyses. Results Approximately 56% of the participants in this dataset were vitamin D deficient ( < 20 ng/mL) with more men (63%) being vitamin D deficient compared to women (51%). Severe vitamin D deficiency ( < 10 ng/mL) was found in 6% of men and 11% of women. Approximately 10% of the participants were sufficient in vitamin D (>30 ng/mL). Weight, BMI and waist circumference were positively associated with vitamin D deficiency. For example, compared to individuals in the lowest category of waist circumference, those in the highest category were at greater than 2-fold higher risk of being vitamin D deficient (OR =  2.29; 95%CI: 1.73 – 3.36; P-trend =  0.001). However, there was no significant association between 25(OH)D levels and metabolic syndrome (OR =  0.75, 95%CI: 0.49 – 1.15; P-trend 0.18) or diabetes (self-reported diabetes: OR =  0.99, 95%CI: 0.59 – 1.68; P-trend 0.85 and diabetes defined by HbA1c levels: OR =  1.09, 95%CI: 0.61 – 1.95; P-trend 0.82) in this study. However, 25(OH)D was associated with higher levels of circulating triglycerides after multivariate adjustments (OR =  0.49, 95%CI: 0.32 – 0.76; P-trend 0.002).

Conclusion

Obesity was associated with vitamin D deficiency in this Qatari dataset. However, 25(OH)D was not associated with diabetes, metabolic syndrome or metabolic factors. Greater adiposity may lead to low vitamin D levels but lower vitamin D levels do not seem to predispose to poor metabolic health. Further causal investigations need to be conducted on the associations between serum vitamin D and obesity, metabolic syndrome and diabetes.