Can the supplementation of vitamin D, sun exposure, and isolation during the COVID-19 pandemic affect the seasonal concentration of 25(OH)D and selected blood parameters among young soccer players in a one-year training season?

ABSTRACT

Objective

This study examined the effect of vitamin D supplementation, sunlight radiationradiation, and home isolation during the COVID-19 pandemic on the seasonal changes in 25(OH)D concentration and selected biomarkers in young soccer players along a one-year training cycle.

Method

Forty elite young soccer players (age: 17.2 ± 1.16 years, body mass: 70.2 ± 5.84, and body height: 179.1 ± 4.26 cm) participated in the research. Only 24 players completed the measurements during all four time- points (T1-: September 2019, T2-: December 2019, T3-: May 2020, and T4-: August 2020) and were divided into two subgroups: supplemented group (GS) and placebo group (GP). Players from GS received 5,000 IU of vitamin D for 8 weeks (January-MarchJanuary–March 2020). Several biomarkers such as 25(OH)D, white blood cells (WBC), red blood cells (RBC), hemoglobin (HGB), muscle damage markersmarkers, and lipid profile were measured.

Results

AnalysisThe analysis of the total group demonstrated significant seasonal changes in 25(OH)D, HGB, asparagine aminotransferaseaminotransferase, and creatine kinase along the one1-year training cycle. The level of 25(OH)D concentrationinconcentration in T4 was significantly (p < 0.001, pη [ = 0.82) higher in both subgroups in comparison to T2 and T3. Moreover, the significant (p = 0.023) but poor (r = −0.23) correlation between 25(OH)D and WBC was calculated.

Conclusion

Current research confirmed the significant seasonal changes in 25(OH)D concentration during four seasons. 8-weekEight-week vitamin D supplementation had no extended effect on the level of 25(OH)D concentration.

KEYWORDS:

• Supplementation
• football
• home-based training
• COVID-19

Authors’ contribution

JJ – conceptualized, designed, and developed the study and prepared the manuscript draft, MS and ŁR – developed the study and performed the data analysis together with GFLS; LH and KW – helped in designing the project and prepared the final version of the manuscript. BK – critically revised the manuscript and supervised the project.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Ethics approval and consent to participate

In accordance with the Helsinki Declaration of 2013, the Local Bioethics Medical Committee in Gdansk (Poland) approved the experiment and agreed to the study (KB consent number−26/19).

Consent for publication

All authors approved the final version of the paper.

Availability of data and material

The data presented in this study are available on request from the corresponding author.

Additional information

Funding

This research did not receive any external funding.