High‐dose vitamin D repletion‐related falls and fractures: An uncontrolled mobility gain?

To the Editor: Recently, Sanders et al. [1] reported the results of a placebo-controlled trial on the efficacy of a single annual oral dose of 500,000 IU of cholecalciferol in the prevention of falls and fractures among older women at high risk of fracture. The findings showed a transient increase in serum vitamin D concentrations among the treated group accompanied by a significant and transient increase in falls and fractures compared to the placebo group. These elements of accountability seem to contradict previous literature in favor of an efficacy of vitamin D repletion against falls and fallrelated fractures [2–4]. The authors thus suggested that ‘‘high serum levels of vitamin D or metabolites resulting from the large annual dose [. . .] might be cause’’ of falls and fractures [1], which was subsequently explained by DawsonHughes and Harris by a greater statistical probability of falls due to vitamin D repletion-induced increase in mobility [5]. It should yet be noted that more mobility does not necessarily expose to more falls since most of active older adults with high mobility and normal vitamin D status do not fall [2,6]. Based on this observation, we propose that the authors were only partly right. We suggest that the steroid action of a large dose of vitamin D given at once, although suddenly improving muscles function [2,3] and mobility level such as gait speed or acceleration capability [6], takes longer to develop in the central nervous system [7]. Such a delay between the improvement of muscles function and the optimization of motor control could be source of transient unsteadiness and explain the increased number of falls during the 3-month period immediately following the high-dose vitamin D repletion. For illustration, it could be compared to driving a city car usually and then suddenly being given a sports car: you would obviously go faster but, unless receiving specific training, you would also drive less safely and be more exposed to car accidents. In other words, if a loading dose of vitamin D improves the quantitative dimension of gait, it could not immediately affect the qualitative one unless being coupled to reeducation and motor learning [8], which was not the case in the study reported by Sanders et al. [1]. In conclusion, the increase in relative risks of falls and fractures observed early after the loading dose of vitamin D compared to placebo group could be explained by the inability to control the new acquired mobility gain, leading to unsafe gait and higher risks of falls and fall-related fractures.