Serum 25-hydroxyvitamin D and physical performance in postmenopausal women.

Background: Impairments in physical performance increase sharply with age. Low serum 25-hydroxyvitamin D (25-OHD) levels may be a modifiable risk factor for physical performance decline.
Methods: Five hundred thirty-two participants in the Women's Health Initiative Clinical Trial (WHI CT) were among a 25% randomly selected subsample of women who participated in performance-based measures of physical performance at baseline, year 1, year 3, and year 6. A physical performance summary score was derived from three tests: timed walk, chair-stand, and grip strength. Levels of 25-OHD were measured at baseline. We used the generalized estimating equations (GEE) method to examine repeated measures of physical performance as a function of follow-up time since baseline according to 25-OHD concentration.
Results: In 6 years of follow-up, participants with serum 25OHD ≥75 nmol/L had significantly higher scores for physical performance (β=2.64, 95% confidence interval [CI] 0.90-4.39) compared with the reference category (<35 nmol/L) after adjustment for age, chronic conditions, body mass index (BMI), race/ethnicity, time spent walking outside, trial arm, clinic latitude, and season of blood draw. However, the rate of decline in physical performance did not differ by level of 25OHD.
Conclusions: Higher baseline serum 25-OHD was associated with better physical performance but did not reduce decline in physical performance over the 6-year period.