5. Conclusions
Vitamin D supplementation plays a central role in covering vitamin D needs. Especially in winter months, when the UV index is too low for endogenous vitamin D synthesis, a carefully planned supplementation strategy is crucial. This research aimed to test the application of Groningens formula to increase the vitamin D needs of athletes and the establishment of an individual supplementation strategy for athletes. This study illustrated that an individualized approach for insufficient vitamin D status correction offers a more reliable and controlled strategy than a standardized approach. However, this also raises the question of the exact doses for the loading and maintenance phases. Daily doses of 4000 IU were effective in correcting insufficient vitamin D status. However, the daily maintenance dose for athletes should be higher than 1000 IU to maintain a 25(OH)D concentration of 40 ng/mL throughout the winter months. Based on these conclusions, practitioners should consider regular vitamin D monitoring throughout the winter months combined with a personalized vitamin D strategy. The methodology employed in this study, which entails independent and decentralized sample collection coupled with an individualized supplementation regimen, is well suited for application in sports settings. This approach could serve as a model for further investigations, such as the examination of the effects of varying loading and maintenance doses in different types of athletes.