Vitamin D and its effect on the endothelial function of cross-country skiers at various stages of the training cycle

Abstract

The aim of the study was to assess the level of vitamin D and nitric oxide metabolites, and to search for the relationship between them in cross-country skiers at various stages of the training cycle. During the year, two groups of men (20–26 years old, inhabitants of the Komi Republic) were examined four times: cross-country skiers who are active members of the national teams of the Komi Republic/Russia (n = 11) and office workers (n = 10). It was shown that skiers had higher vitamin D levels duration the year compared to office workers. The fluctuations in the levels of vitamin D, calcium and phosphorus detected in cross-country skiers were seasonal, which could lead to significant changes in the synthesis of nitric oxide and the work of the endothelial system. The greatest number of correlations between the studied metabolites in cross-country skiers was revealed at the beginning and end of the annual training season. A significant imbalance in the levels of vitamin D and nitric oxide metabolites found in them in March may negatively affect the success of performance at important competitions.