OBJECTIVETo investigate the association between the polymorphism of vitamin D receptor (VDR) gene start codon (Fok I) and bone mass accrual, and assessing if such an association could be modified by physical activity in Chinese adolescent girls.

METHODSA total of 228 premenrche Chinese girls (9-11.5-years-old) were recruited for 2-year study. Bone mineral densities (BMD) at the total body, total left hip (including femoral neck, trochanter, intertrochanteric and Ward's triangle area) and lumbar spine (L1-L4) were measured by dual energy X-ray absorptiometry. The Fok I polymorphism of VDR gene was detected with PCR-RFLP.

RESULTSThere remained 176 available subjects in our cohort when 2-year study was completed. No significant association was observed between Fok I polymorphism of VDR gene and percentage change in BMD at all sites. Girls with FF genotype had lower percentage change in total left hip BMD (THBMD) and femoral neck BMD (FNBMD) than girls with Ff + ff genotype only in low physical activity(< 1197 kJ/d), and physical activity was associated with percentage change in THBMD and FNBMD only in FF genotype group.

CONCLUSIONThe Fok I polymorphism of VDR gene should have significant interaction effect with physical activity on bone mass accrual in Chinese adolescent girls. Girls with FF genotype in low physical activity would be the potential risk population for low bone mass accrual, and high physical activity would be of benefit to gain higher bone mass accrual for girls with FF genotype.