Vitamin D and muscle in chronic kidney disease

Abstract

Skeletal muscle is frequently impacted in uraemic patients with both mechanical and metabolic consequences. Muscle wasting, weakness and structural changes, fundamentally as atrophy of type II muscle fibers, but also insulin resistance are common and however readily overlooked. Beyond a negative effect on physical activity and quality of life, skeletal muscle loss was reported to be also a powerful and independent predictor of survival, at least partly in relation with insulin resistance. Muscle loss in uraemic patients appears to be multifactorial. Among the different mechanisms liable to contribute to muscle wasting vitamin D defi- ciency, which is present in 50-80 % of incident dialysis patients, is a well-known factor of reduction of muscle mass, strength, physical performance and of increased risk of falls. In these circumstances, vitamin D supplementation appears to be a reasonable, simple and potentially adequate therapy. Vitamin D supplementation seems to be an effective strategy to replenish vitamin D stores and to control PTH and more scarcely other biochemical endpoints. As only few observational studies have been performed, there are not enough data to draw definitive conclusions about the effects of natural vitamin D supplementation on patients’ outcomes, including mortality, and a fortiori on muscle disorders and their mechanical and metabolic consequences. Large, well-designed, randomized controlled trials are still requested to assess the possible benefits of natural vitamin D supplementation on skeletal muscle in CKD patients.