|Not the ideal soccer weather. If you put faith in the authors' interpretation of the results, soccer is a game that must be played in the sun. Why? Well, to maximize the vitamin D production ;-)|
The authors speculated that in both experimental sessions vitamin D levels would correlate with soccer players’ jumping, sprinting, and aerobic capacity, and that the off-season transition period, of reduced training stress, would favorably affect vitamin D concentration.
As we are about to see a few lines below, this is exactly what Nikolaos E. Koundourakis and his colleagues found in what is "to the best of [the researchers] knowledge" the first study to examine the relationship "between vitamin D levels and muscle strength, VO2max and speed in professional soccer players, and/or the effects off-season detraining soccer period on its levels in any kind of athletic population." (Koundourakis. 2014)
|Table 1: Correlations (correlation coefficients and p-values) between Vitamin D levels and exercise performance parameters; pre = acute pre-season training vs. post = after six-week off-season transition period (Koundourakis. 2014)|
These observations highlight the importance of adequate sun exposure and raise the question, whether it wouldn't be prudent to supplement with 2.000IU of vitamin D per day during the winter months to avoid the reduction in vitamin D levels in the first place.
"In our study the six-week transition period had a boosting effect on vitamin D levels. Indeed, at the first experimental period,although none of our participants was vitamin D deficient (<20 ng/ml) or severe deficient (<10 ng/ml), 55,22% of our players had insufficient vitamin D levels (<30 ng/ml), whereas at the second one only 4,47% were found to be below 30 ng/ml. [...] The most plausible explanation for the elevation of vitamin D levels at the second experimental session could be the consequence of an increased exposure to UVB during the off-season period.
Suggested Read: Leucine, Insulin & Vitamin D: A Hypertrophy Boosting Triplet That Does Not Make It From the Dish to the Gym? | read more
Indeed, this transition period in Greek Superleague takes place during June and at the beginning of July at a favorable latitude (35,9°N). During this period UVB reaches its peak, resulting in increased vitamin D production." (Koundourakis. 2014)
- Koundourakis, Nikolaos E., et al. "Vitamin D and Exercise Performance in Professional Soccer Players." PLOS ONE 9.7 (2014): e101659.
- Waldron, Jenna Louise, et al. "Vitamin D: a negative acute phase reactant." Journal of clinical pathology (2013): jclinpath-2012.