Vitamin D status and relationship between vitamin D and risk factors of metabolic syndrome : a study in Taiyuan City in China : a thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Human Nutrition at Massey University, Manawatu, Palmerston North, New Zealand

Abstract

Background Vitamin D deficiency is widespread, and the residents in Taiyuan City in China seem to be at high risk of vitamin D deficiency. The situation might be because the city is located in north China and air pollution in the city is heavy. Meanwhile, emerging evidence suggests that vitamin D deficiency may be associated with prevalence of metabolic syndrome (MetS), which usually progress to diabetes and increases the risk of cardiovascular disease. MetS has been becoming much more common in China, and even affects younger people. Objectives This study investigated the vitamin D status of non-manual workers living in Taiyuan City; and explored the relationship between vitamin D status and markers of MetS in 200 participants attending the Health 100 Check-up Center in Taiyuan City for their usual health check. Methods In this cross-sectional study; 200 non-manual workers aged 20-80 years old, living in Taiyuan City were recruited. The participants had their serum vitamin D levels measured and were asked questions about their lifestyle, including daily exercise, alcohol use and smoking. The Check-up Center provided data relating to MetS of the participants. These data included anthropometrics (height, weight and body circumferences), biochemical data (lipid profiles and fasting glucose from blood samples taken for the check-up) and blood pressure. Results Seventy eight percent of participants had vitamin D values less than 50 nmol/L. The women’s serum 25-hydroxyvitamin D (25(OH)D) status (median; 32.70 nmol/L (upper and lower quartile; 25.80, 43.80)) was significantly lower than that of the men (44.00 nmol/L (32.30, 55.40)) (p<0.01). In females aged younger than 40 years vitamin D status (29.25 nmol/L (24.05, 40.85)) was significantly lower than older participants (age>65). In the present study, multiple linear regressions showed the determinants of the vitamin D status were female gender, smoking, and increased fasting glucose (p<0.05). The prevalence of MetS, or abdominal obesity between the groups with and without vitamin D insufficiency were not significantly different (p=0.08; p=0.07). Multiple logistic regression analysis showed that vitamin D status was not associated with MetS. Conclusions Vitamin D insufficiency was highly prevalent in non-manual workers in Taiyuan City in China during the winter season. Vitamin D status in the women was lower than the men. Among the females, younger women had worse vitamin D status than the older women. So, in the present study, female gender, increased fasting glucose, and smoking were significant determinants for vitamin D insufficiency. Vitamin D insufficiency was not associated with the risk factors for MetS in the present study. However, female gender, increased waist circumference (WC), and raised serum triglycerides were associated with higher risk of MetS.