Vitamin D and parathyroid hormone are associated with gait instability and poor balance performance in mid-age to older aged women

Context: Vitamin D status and parathyroid hormone (PTH) levels influence the risk of accidental falls in older people, but the mechanisms underlying this effect remain unclear. Objective: Investigate the relationship between circulating PTH and 25 hydroxyvitamin D (25-OHD) levels and clinical tests of gait stability and balance as physical fall risk factors. We hypothesized that high levels of PTH and low 25-OHD levels would be significantly associated with gait stability and decreased balance performance. Design: Observational cohort study. Setting: Australian community. Participants: 119 healthy, ambulatory female twin adults aged 47-80 years residing in Victoria, Australia. Outcome measures: Serum PTH and 25-OHD levels with clinical tests of gait stability [double support duration (DSD)] and dynamic balance (Step Test). Associations were investigated by regression analysis and by comparing groups divided by tertiles of PTH (< 3.5, 3.5-4.9,> 4.9 pmol/L) and 25-OHD (< 53, 53-75,> 75 nmol/L) using analysis of variance. Results: Serum PTH was associated positively with DSD, with an increase of 10.6-15.7% when the mid and highest PTH tertiles were compared to the lowest tertile (p < 0.025) when 25-OHD was included in the regression analysis. 25-OHD was significantly associated with DSD (greater by 10.6-11.1% when lowest and midtertiles compared with the highest 25-OHD tertile) (p < 0.025) and dynamic balance (better performance by 12.6% in the highest compared with the lowest 25OHD tertile) (p < 0.025). Conclusion: These findings reveal an important new relationship between parathyroid hormone and gait stability parameters and add to understanding of the role of 25-OHD in motor control of gait and dynamic balance in community-dwelling women across a wide age span.