The active form of vitamin D (calcitriol) exerts its biological effects by binding to nuclear vitamin D receptors (VDRs), which are found in most human extraskeletal cells, including skeletal muscles. Vitamin D deficiency may cause deficits in strength, and lead to fatty degeneration of type II muscle fibers, which has been found to negatively correlate with physical performance. Vitamin D supplementation has been shown to improve vitamin D status and can positively affect skeletal muscles. The purpose of this study is to summarize the current evidence of the relationship between vitamin D, skeletal muscle function and physical performance in athletes. Additionally, we will discuss the effect of vitamin D supplementation on athletic performance in players. Further studies are necessary to fully characterize the underlying mechanisms of calcitriol action in the human skeletal muscle tissue, and to understand how these actions impact the athletic performance in athletes.

Vitamin D is mainly known for its effects on the bone and calcium metabolism. The discovery of Vitamin D receptors in many extraskeletal cells suggests that it may also play a significant role in other organs and systems. The aim of our study was to assess the relationship between 25(OH)D₃levels, lower limb isokinetic strength and maximum oxygen uptake in well-trained professional football players. We enrolled 43 Polish premier league soccer players. The mean age was 22.7±5.3 years. Our study showed decreased serum 25(OH)D₃levels in 74.4% of the professional players. The results also demonstrated a lack of statistically significant correlation between 25(OH)D₃levels and lower limb muscle strength with the exception of peak torque of the left knee extensors at an angular velocity of 150°/s (r=0.41). No significant correlations were found between hand grip strength and maximum oxygen uptake. Based on our study we concluded that in well-trained professional soccer players, there was no correlation between serum levels of 25(OH)D₃and muscle strength or maximum oxygen uptake.

A well-balanced diet is one of the main factors that may play a supportive role in enhancing acute training stimuli in optimal training adaptation. The aim of the present study was to examine the energy and macro- and micronutrient intake including and excluding supplements among top-level Polish football players during one week of the general preparatory period. In addition, the study looked at whether athletes consume carbohydrates in recommended amounts, depending on the completed training sessions. A total of 26 professional football players were included in the study. The preseason dietary intake was assessed using a 7-day estimated food record. The energy value of the diet and the amounts of the dietary ingredients were assessed using the software Dieta 6.0. The average consumption of energy, vitamin B₂, vitamin C, vitamin E, folate, and calcium was lower than recommendations, and average intake of sodium and potassium was higher than the norm in the diets of the athletes. The results of this study do not confirm the justification for adding protein preparations to diets of the studied players. Furthermore, football players dietary carbohydrate intake was relatively low in comparison to requirements based on training loads. Based on our results we conclude that further work is necessary to reinforce education about nutritional habits and adjust nutritional strategies to individual needs to enhance athletic performance.

The aim of this review was to determine whether male football players meet dietary recommendations according to a UEFA expert group statement and to identify priority areas for dietetic intervention, including training periodization and field position. A database search of PubMed, Web of Science, EBSCO and Scopus was performed. To be included within the final review, articles were required to provide a dietary intake assessment of professional and semi-professional football players. A total of 17 studies met the full eligibility criteria. Several studies showed insufficient energy and carbohydrate intake compared to the recommendations. A majority of athletes consume adequate protein and fat intakes compared to the recommendations. In addition, several studies showed the insufficient intake of vitamins and minerals. This systematic review showed that football players do not meet the nutritional recommendations according to the UEFA expert group statement. Future research should be focused on how to apply nutritional recommendations specific for athletes in accordance with training periodization and positions on the field.

The use of dietary supplements is widespread among athletes, with intake influenced by factors such as sport-discipline, competitive level, and gender. The Australian Institute of Sport (AIS) has categorized supplements based on scientific evidence regarding their efficacy and safety. Despite extensive global research on dietary supplement use among athletes, data on Polish athletes remain limited. Therefore, this study aimed to evaluate supplement use among Polish athletes, considering their competitive level and gender. Additionally, it assessed whether athletes select supplements in accordance with the AIS classification and examined their awareness of supplement certification programs. This cross-sectional study included 659 Polish athletes (309 women, 350 men) from various sports, representing both professional (57.7%) and nonprofessional (42.3%) levels. An online questionnaire was used to assess dietary supplement consumption, sources of information regarding supplementation, and knowledge of anti-doping and supplement certification programs. Supplement use was categorized according to the AIS classification (Groups A - D). Statistical analyses, including chi-square tests and Mann - Whitney U tests, were conducted to evaluate differences between professional and nonprofessional athletes, as well as between male and female participants. A high prevalence of dietary supplement use (91.1%) was observed among Polish athletes, with no significant differences between professional (95.8%) and nonprofessional (94.3%) athletes or between men (92.0%) and women (90.0%). The most frequently consumed supplements were sports drinks (63.9%), electrolyte supplements (51.6%), and isolated protein supplements (54.6%), vitamin D (71.6%), vitamin C (59.8%), with significantly higher intake among professional athletes. Male athletes were more likely than females to consume caffeine (p < 0.001), creatine (p < 0.001), and β-alanine (p < 0.001). Melatonin use was significantly higher among professionals (p < 0.05). Awareness of WADA regulations was moderate (72.7%), but knowledge of supplement certification programs was low, with only 18.2% of professional athletes familiar with Informed Sport, and 10.7% with the Cologne List. Social media was the most common source of supplement information (41.9%), while only 17.6% of athletes consulted qualified specialists in sports nutrition and supplementation area. This study highlights the widespread use of dietary supplements among Polish athletes, irrespective of competitive level or gender. While many athletes select supplements from AIS Group A, their knowledge of AIS classification and supplement certification programs remains limited. The high reliance on social media for supplement information, combined with the lack of professional guidance, underscores the need for improved education on safe and effective supplementation practices. Given the risks associated with supplement contamination, targeted initiatives should enhance athletes' awareness of anti-doping regulations and certified supplement options.