Effect of a single oral dose of 600,000 IU of cholecalciferol on muscle strength: A study in young women

Background: The effect of a single large oral dose of vitamin D on muscle function in young people with vitamin D deficiency has not been investigated so far. Aim: We evaluated the effect of a single oral dose of 600, 000 IU of cholecalciferol on muscle strength. Subjects and methods: Eighteen young women with vitamin D deficiency received a single oral dose of 600, 000 IU of cholecalciferol. We evaluated changes in maximal voluntary contraction (MVC) and speed of contraction (S) in response to cholecalciferol by using an hand held dynamometer at 3, 15, 30, 60 and 90 days, compared to baseline. Results: We observed no significant change in MVC and S values, a significant increase of 25-hydroxyvitamin D [25(OH)D] and 1, 25-dihydroxyvitamin D [1, 25(OH)2D] and a significant decrease in serum parathyroid hormone (PTH) (p<0.001 for all). A significant correlation was found between MVC and S and serum phosphorus (P) after supplementation (p<0.02 and p<0.05, respectively). Conversely, we observed no association between the parameters of muscle strength and 25(OH)D, ionized calcium (Ca2+), PTH and 1, 25(OH)2D. Conclusions: A single dose of 600, 000 IU of cholecalciferol does not directly enhance handgrip strength in young women with vitamin D deficiency. More studies are needed on the indirect effect of the hormone on muscle.