Objective: To investigate the association of polymorphisms of start codon (Fok I site) and CDX2 binding site in vitamin D receptor gene (VDR) concerned with the effect of calcium supplementation on bone mineral density (BMD) and bone turnover markers of postmenopausal women.
Methods: Two hundreds unrelated postmenopausal women of Han ethnicity in Shanghai were randomly divided into 2 groups of 100 women: high calcium group (1000 mg element calcium and 400 units of vitamin D were given daily for 12 months) and low calcium group (300 mg element calcium and 300 units of vitamin D were given daily for 12 months). BMD and bone turnover markers were measured at baseline and 12 months after calcium supplementation. VDR gene Fok I and CDX2 polymorphisms were analyzed using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and allele-specific multiplex PCR, respectively.
Results: One hundred and seventy-one women completed 12-month study period. The frequency of VDR Fok I genotypes was 48.0 % for Ff, 31.0 % for FF, and 21.0 % for ff, and the frequency of CDX2 genotypes was 56.7 % for AG, 25.7% for GG, and 17.6% for AA. The frequencies distribution of Fok I and CDX2 alleles in the entire population or in two subgroups all followed the Hardy-Weinberg equilibrium. No significant difference of baseline BMD and bone turnover markers in Fok I genotypes or CDX2 genotypes was observed in the entire population or in two subgroups. Moreover, regardless of calcium supplementation given for 12 months, no significant association was found between Fok I or CDX2 polymorphisms and the endpoint values or percentage changes of any BMD and bone turnover markers in either high calcium group or low calcium group.
Conclusion: There is no significant relationship between VDR gene Fok I or CDX2 polymorphisms and the effect of high or low doses calcium supplementation on BMD and bone turnover markers in Shanghai postmenopausal women of Han ethnicity.