Vitamin D in exercise: physiologic and analytical concerns.

Despite a wide number of studies performed on the general population, little is known about the Vitamin D status of athletes. A particular influence of many factors, including skin pigmentation, early- or late-day training, indoor training, geographic location and extensive sunscreen use, has been observed in this specific population. The need of supplementation with Vitamin D in athletes is not defined or, when supplementation is needed, even the optimal amount of Vitamin D to be used is not specified. The periodic measurement of Vitamin D is the only procedure capable to define athletes' status. Although various methods for the measurement of Vitamin D are routinely used, they often give discordant and poorly reproducible results; thus, it is necessary to standardize the various methods, in order to have comparable results. In conclusion, current available data indicate both that little is known about the Vitamin D status of athletes and that is still unclear if supplementation could be desirable. Finally, it must be pointed out that all the papers about Vitamin D status should indicate in detail the method used for really allowing a correct interpretation of data.