Table 5.

The main limitations of the different studies of the meta-analysis.

Study	Limitations
Nieman et al., 2013 [32]	Physical activity consists in a very specific job, difficult to compare with other sport disciplines. Small sample size. Gender not specified (likely men). Supplementation with ergocalciferol.
Shanely et al., 2014 [33]	Information regarding the physical activity performed is limited, being complicated the comparison with other studies. Analytical method for vitamin D determination: chemiluminescent immunoassay. Performed only in men. Supplementation with ergocalciferol.
Parsaie et al., 2019 [34]	Analytical method for vitamin D determination: immunoassay. Small sample size. Gender not specified. Differences in baseline BMI between groups.
Ashtary-Larky et al., 2020 [35]	The exact type of endurance activity is not indicated. Analytical method for vitamin D determination: immunoassay (ELISA). Small sample size. Performed only in men. Short duration.One dose of vitamin D.
Pilch et al., 2020 [36]	Subjective control of the physical activity performed. The intensity is difficault to compare with other studies. Analytical method for vitamin D determination: immunoassay (ELISA). Performed only in men.
Żebrowska et al., 2020 [37]	Analytical method for vitamin D determination: no indicated. Small sample size. Performed only in men.