Not all elderly people benefit from vitamin D supplementation with respect to physical function: results from the Osteoporotic Fractures in Men Study, Hong Kong

Objectives: To examine vitamin D status and its association with physical performance and muscle mass in older Chinese men.

Design: Cross-sectional and prospective cohort study design.

Setting: Hong Kong, People's of Republic of China.

Participants: Nine hundred thirty-nine community-dwelling men aged 65 and older for cross-sectional analysis and 714 for longitudinal analysis.

Measurements: Baseline serum 25-hydroxyvitamin D (25OHD) was measured using a competitive radioimmunoassay kit. Baseline and 4-year physical performance measures (grip strength, 6-m walking speed, step length in a 6-m walk, time to complete five chair stands) were measured, and appendicular skeletal muscle mass (ASM) was assessed using dual-energy X-ray absorptiometry. Data were collected for confounding factors: demographic, number of diseases, smoking, alcohol use, body mass index, physical activity, diet, season of blood sampling, and serum parathyroid hormone (PTH) level. Multivariate regression analyses were performed with adjustments for confounding factors.

Results: Mean ± standard deviation serum 25OHD level of this sample of Chinese community-dwelling older men who had a high level of baseline physical function was 77.9 ± 20.5 nmol/L; 94.1% of participants had serum 25OHD levels of 50 nmol/L or greater. Median (interquartile range) serum PTH level was 4.1 pmol/L (3.1-5.5 pmol/L). After adjustment for potential confounding factors, serum 25OHD levels were not associated with baseline or 4-year change in physical performance measures and ASM.

Conclusion: In Chinese older men who are vitamin D replete and have a high level of baseline physical function, vitamin D may not have an important role in physical function and muscle mass.