Football players with higher vitamin D levels achieve better training results and physical performance, according to new research from the Academy of Physical Education in Katowice. The findings were published in the journal Frontiers in Physiology.
“For years, vitamin D was associated almost exclusively with the skeletal system,” said Dr. Małgorzata Magdalena Michalczyk, a professor at the Academy and the study’s lead author. “The discovery of its receptor in virtually every cell in the body led scientists around the world to explore its broader role, also in muscles. It turned out that—just like in bones—it regulates calcium levels, which are essential for muscle contraction. Therefore, it indirectly affects muscle function.”
Michalczyk said her team wanted to determine whether vitamin D levels at the start of preseason training influenced athletes’ progress. “We decided to test whether vitamin D levels at the beginning of the players’ preseason would impact their progress during training and the development of their athletic performance,” she explained.
The study involved 20 Polish professional footballers tested during winter, at the start of preseason. Researchers measured blood concentrations of 25(OH)D, the main form of vitamin D, and then observed the players over six weeks of technical, tactical, strength, and endurance training.
At the start and end of the period, the athletes completed sprint and agility tests, including 5- and 30-meter runs and a direction-change drill.
“Based on their blood vitamin D levels, we divided them into two groups,” Michalczyk said. “One group had too low levels (below 30 ng/ml), and the other group had normal levels (above 30 ng/ml). It turned out that players with lower levels achieved significantly worse results than those with normal levels.”
While vitamin D did not affect straight-line sprinting speed, the differences were clear in agility-based tests. “Players with higher vitamin D levels improved significantly more in these areas over six weeks than those with low levels,” Michalczyk said.
“In practice, this means that an athlete with low vitamin D levels, training at the same intensity, may not achieve the same results as a teammate with adequate levels of this nutrient,” she added. “This is valuable information for coaches and training staff.”
The researchers also noted that half of the footballers tested had insufficient vitamin D, and one in five showed significant deficiency, with levels below 20 ng/ml.
Michalczyk said awareness of vitamin D’s role is improving but remains incomplete. “Public awareness of the role of vitamin D is growing, but is primarily limited to its importance for the skeletal and immune systems,” she said. “Meanwhile, research in recent years has shown that its role in the body is much broader.”
Previous studies show that vitamin D indirectly affects athletic performance by regulating calcium metabolism — key to muscle contraction — and influencing the expression of more than 900 genes related to muscle protein synthesis, energy metabolism, and hormonal balance. “Its effect on testosterone levels, which promotes muscle mass and strength gains, may also be important,” Michalczyk said. “All this may explain why higher vitamin D levels promote better athletic performance.”
Michalczyk stressed the practical implications for professional sports. “Vitamin D testing is relatively expensive, and many Polish football clubs forgo it,” she said. “Testing a single player costs several dozen zlotys, and there are dozens of people on a team. Meanwhile, our results show that even a single measurement taken at the beginning of the preparation period provides valuable information. It allows us to predict whether a given athlete is at risk of poor progress and whether supplementation should be implemented.”
Earlier research by the same team found that vitamin D supplementation improved both biochemical markers and performance outcomes in athletes. “A few years ago, we conducted studies using 6,000 units of vitamin D3. We observed beneficial effects in terms of speed and muscle strength,” Michalczyk said. “In the future, we would like to examine the results of higher doses and longer supplementation programs.”
She also warned that most Poles are deficient in vitamin D, a condition that can lead to chronic fatigue, muscle weakness, bone and joint pain, frequent infections, and mood problems.
PAP - Science in Poland, Katarzyna Czechowicz (PAP)
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