Single-Nucleotide Polymorphisms (SNPs) in Vitamin D Physiology Genes May Modulate Serum 25(OH)D Levels in Well-Trained CrossFit® Athletes, Which May Be Associated with Performance Outcomes

Vitamin D is a key micronutrient in the function of the skeletomuscular system. Athletes are at increased risk of developing vitamin D deficiency during the execution of very demanding disciplines such as CrossFit^®. Single-nucleotide polymorphisms (SNPs) may influence circulating 25-hydroxy-vitamin D (25(OH)D) levels. An observational, longitudinal pilot study was conducted with 50 trained males according to specific inclusion criteria. Blood samples were obtained to determine <i>25(OH)</i>D, <i>vitamin D-binding protein</i> (<i>VDBP</i>), <i>vitamin D-receptor</i> (<i>VDR</i>)circulating levels, and the presence of SNPs after DNA isolation and genotyping: rs10741657 to <i>CYP2R1</i>, rs2282679 to <i>GC</i> and rs2228570 to <i>VDR</i> genes. Significant differences (<i>p</i> < 0.05) in 25(OH)D concentration were determined between the biallelic combinations of rs228679 (<i>GC</i>) and rs228570 (<i>VDR</i>). The VDBP and VDR proteins did not show different levels in the case of the rs10741657 (<i>CYP2R1</i>) alleles. Statistically significant weak positive correlations (<i>p</i> < 0.05) were observed between 25(OH)D and AA-alleles of the <i>CYP2R1</i> and <i>VDR</i> genes, and TT-alleles of the <i>GC</i> gene. Additionally, <i>AA</i> (rs10741657 and rs2228570) and <i>TT</i> (rs2282679) have a probability between 2 and 4 of having major effects on the concentration of 25(OH)D. Conversely, <i>GG</i> alleles present a probability of suboptimal values of 25(OH)D of 69%, 34%, and 24% for <i>VDR</i>, <i>GC</i>, and <i>CYP2R1</i>, respectively, showing a strong moderate positive correlation (r = 0.41) between the degrees of sports performance and 25(OH)D plasma levels. <i>CYP2R1</i> (rs10741657), <i>GC</i> (rs2282679), and <i>VDR</i> (rs2228570) affect the concentration of serum 25(OH)D, as an indicator of vitamin D status and play a critical role in the sports performance of CrossFit^® practitioners.