Higher 1,25-dihydroxyvitamin D₃ concentrations associated with lower fall rates in older community-dwelling women

Introduction: The purpose of this study was to examine the relationships of vitamin D supplementation and serum concentrations of vitamin D metabolites and parathyroid hormone (PTH) with neuromuscular function and falls in older community-dwelling women. Methods: We examined these relationships using a 4-year prospective multi-center study among 9,526 community-dwelling women enrolled in the Study of Osteoporotic Fractures (median age: 70 years; interquartile range: 67-75) and a subset of 389 women (97%) out of 400 who were randomly selected from the entire cohort for serum measures. Measurements included: vitamin D supplementation, serum 25-hydroxyvitamin D₃ [25(OH)D₃], serum 1,25-dihydroxyvitamin D₃ [1,25(OH) ₂D₃], and serum intact parathyroid hormone (iPTH); grip and quadriceps strength, chair-stand time, walking speed, reaction time, and balance-walk time (including changes in grip strength, chair-stand time, walking speed and balance-walk time over approximately 3.7 years); and incident fall rates (number of falls/woman-years). Results: In 9,526 women, vitamin D supplementation was not associated with any measures of neuromuscular function, change in neuromuscular function, or fall rates (p>0.01 for all). In a subgroup of 389 women, there was a trend of higher 25(OH)D₃ concentration with slightly weaker grip strength (p=0.007), and women in the fourth quartile of 1,25(OH)₂D₃ had a faster chair-stand time (p=0.017) than women in the first quartile; still, in general, concentrations of 25(OH)D₃, 1,25(OH)₂D₃, and iPTH were not associated with either neuromuscular function or changes in neuromuscular function (p>0.05 for all). However, higher 1,25(OH) ₂D₃ concentration was associated with lower fall rates (p=0.039). Conclusions: Higher 1,25(OH)₂D₃ concentration is associated with a lower fall risk in older community-dwelling women, but vitamin D supplementation, and 25(OH)D₃ and iPTH concentrations are not associated with either neuromuscular function or falls.