Serum vitamin D is low and inversely associated with LDL cholesterol in the Kazak ethnic population: a cross-sectional study.

Background: Accumulating evidence suggests that low concentrations of serum 25(OH)D is coupled with increased risks of hypertension, obesity, and cardiovascular disease. However, this relationship has not been established in populations with very low levels of 25(OH)D. Therefore, the aim of our study was to clarify the associations between 25(OH)D and blood pressure, obesity, sex, and lipid profiles in the Kazak ethnic population, who have an extremely low level of 25(OH)D.

Material/methods: A multistage-cluster sampling survey was carried out for residents with Kazak ethnicity in Xinjiang, China. Anthropometric measurements of each participant were taken and the concentrations of 25(OH)D, calcium, alkaline phosphatase, and lipid profiles were measured. Individuals were classified into different groups in terms of vitamin D status, degree of adiposity, presence of hypertension, and other comorbidities.

Results: The madian concentration of 25(OH)D was 16.2 (11.8-20.5) ng/mL and the prevalence of vitamin D deficiency was 72.4% in this Kazak population (n=928, 59.0% women). Females had a lower 25(OH)D concentration than males - 14.6 (10.5-19.4) ng/mL vs. 17.7 (14.8-22.5) ng/mL, P<0.001. The subjects were classified into 3 groups according to their vitamin D status. There were significant differences in BMI (P=0.046), waist circumference (P=0.037), hip circumference (P=0.003), systolic BP (P=0.035), and LDL cholesterol (P=0.008) among the groups after adjustment for sex and age. On the other hand, there was no significant difference in vitamin D levels between groups with or without hypertension (P=0.586), and groups with or without obesity (P=0.639). A multifactor-regression analysis revealed that every increment of 1mg/dL in LDL cholesterol was associated with a 1.0 ng/mL decline in serum 25(OH)D.

Conclusions: The insufficiency of vitamin D is highly prevalent in Kazaks. Sex, LDL cholesterol, and hip circumference are 3 variables strongly associated with serum 25(OH)D concentration. In a population with low levels of 25(OH)D, the negative relationship between obesity and serum 25(OH)D, a common finding from most previous studies, could not be established.