Is serum 25‐hydroxyvitamin D deficiency a risk factor for the incidence of slow gait speed in older individuals? Evidence from the English longitudinal study of ageing

Abstract Aims Cross‐sectional studies demonstrate an association between low serum levels of vitamin D and slower gait speed in older individuals. However, longitudinal studies remain inconclusive. This study investigates whether vitamin D deficiency and insufficiency are risk factors for the incidence of slowness. Materials and Methods A total of 2815 participants from the English Longitudinal Study of Ageing (ELSA), aged ≥60 years and with a baseline gait speed >0.8 m/s, were followed for six years. Baseline serum levels of vitamin D [25(OH)D] were categorized as “sufficiency” (>50 nmol/L), “insufficiency” (>30 and ≤50 nmol/L) or “deficiency” (≤30 nmol/L). Gait speed was reassessed at four and six years of follow‐up to identify incident cases of slowness (walking speed ≤0.8 m/s). A Poisson regression model, adjusted for sociodemographic, behavioural and clinical characteristics at baseline, was conducted to determine the association between serum 25(OH)D levels and the risk of slowness. Results The incidence densities of slowness per 1000 person‐years were 67.4 (95% CI: 60.93–74.64) for sufficiency, 76.7 (95% CI: 68.30–86.22) for insufficiency and 90.7 (95% CI: 78.46–104.92) for deficiency. Serum 25(OH)D deficiency was associated with a 22% increase in the risk of slowness (IRR: 1.22; 95% CI: 1.01–1.49) compared with serum 25(OH)D sufficiency. No significant association was observed for serum 25(OH)D insufficiency. Conclusions Serum 25(OH)D deficiency is a risk factor for the incidence of slowness in older individuals, suggesting that maintaining sufficient 25(OH)D levels could be a strategic approach to minimise long‐term mobility impairment.