The main purpose of this research was to demonstrate the changes in 25(OH)D concentration, bone resorption markers, and physical fitness along the one-year training season in young soccer players. A total of 24 young soccer players (age: 17.2 ± 1.16 years, mass: 70.2 ± 5.84, height: 179.1 ± 4.26 cm) were tested at four different time points across one year (T1—September 2019; T2—December 2019; T3—May 2020; T4—August 2020). After T2 (during COVID-19 lockdown), players were divided into a supplemented (GS) group and a placebo group (GP). Variables such as 25(OH)D, calcium (Ca), phosphorus (P), parathyroid hormone (PTH), aerobic capacity, speed, and explosive power were measured. Analyses performed for all participants indicated significant changes in all selected blood markers and running speed. The highest values in 25(OH)D were noted during summertime in T1 and T4. After individuals were split into two groups, a two-factorial ANOVA demonstrated a significant time interaction for 25(OH)D, Ca, P, PTH, 30 m sprint, and counter-movement jump. Significant time x group effect was calculated for aerobic capacity. This study confirmed that 25(OH)D concentration varies between four seasons, with the greatest decreases in the low sunlight periods. Vitamin D supplementation did not cause a preventive and long-lasting effect of increasing the 25(OH)D concentration in the young soccer players.

The purpose of this study was to investigate the influence of maximal oxygen uptake (VO₂ max) on the glycemic changes during low and high intensity exercises in young type 1 diabetic patients. Twenty boys (age: 14.3 ± 1.6 years; height: 171.0 ± 11.3 cm; weight; 59.5 ± 12.8 kg) were divided into low-fit group (LFG, n = 10) and high-fit group (HFG, n = 10). According to the experimental design, participants performed three physical efforts (VO₂ max test, mixed aerobic–anaerobic effort and aerobic effort) on the cycloergometer, during which real-time glycemia was measured. Mixed aerobic–anaerobic exercise demanded significantly smaller carbohydrate supplementation (0.2 ± 0.2 g/kg during exercise) than the aerobic test session (0.4 ± 0.3 g/kg during exercise). Moreover, patients with higher VO₂ max had lower tendency for glycemic changes during the aerobic effort. The results of the current study suggest that young type 1 diabetic patients should perform different intensity activities using continuous glycemic monitoring system to avoid acute and chronic complications of the disease.

Searching for potential relations between changes in 25(OH)D concentration and in physical fitness is an interesting scientific topic. Thus, the main purpose of this study was to investigate the changes in serum concentrations of 25(OH)D in young football players in conjunction with indicators determining bone resorption and physical fitness. A total of 35 young soccer players were tested during the autumn competition period. Biochemical analysis of blood, aerobic capacity, running speed and power tests (Wingate test, squat jump, counter movement jump) were carried out at the beginning and at the end of the competition period. Significant decrements in concentration of 25(OH)D from 33.9 ± 5.87 to 23.7 ± 5.58 ng/mL were noted after the analyzed competition period. There were no significant changes in aerobic capacity along the competition period. Significant improvements were observed in 10 m sprint, 30 m sprint (p < 0.001), maximal power (p = 0.011) and total work capacity (p = 0.024). We found that the effect of changes in the players’ physical fitness does not occur in relation to 25 OH(D) concentration but occurs when these changes are analyzed as a function of the duration of the observation period. Changes in physical fitness of soccer players are determined by other factors then 25(OH)D concentration.

The main purpose of this study was to investigate the differences in glycaemic reaction in response to various physical activities in 20 young boys (14.4 ± 1.6 years) with type 1 diabetes mellitus (T1DM) and with either vitamin D deficiency or with suboptimal levels of vitamin D. Participants were divided into two groups (deficiency group—DG, n = 10; suboptimal group—SG, n = 10) according to their vitamin D levels. All patients performed aerobic and mixed (aerobic-anaerobic) physical efforts. During the exercise, the respiratory responses and glucose levels were monitored. Biochemical blood analyses were performed before each physical effort. The oxygen consumption was not significantly lower in SG during both aerobic and mixed effort (4.0% and 5.6%, respectively). The glycated haemoglobin (HbA1c) level was higher by 6.1% and the total daily dose of insulin (DDI) was higher by 18.4% in the DG. The differences were not statistically significant. Patients with lower vitamin D levels demonstrated an insignificantly higher glycaemic variability during days with both aerobic and mixed exercises. An appropriate vitamin D concentration in T1DM patients’ blood may constitute a prophylactic factor for hyperglycaemia during anaerobic training and hypoglycaemia during aerobic training.

This study aimed to demonstrate the changes of selected blood parameters in relation to 25(OH)D concentration during the autumn period in young soccer players. A total of 35 participants’ results (age: 17.5 ± 0.6 years, body mass 71.3 ± 6.9 kg) were tested twice: in mid-September and in mid-December and divided into subgroups with regard to two criteria. First, according to the initial level of the 25(OH)D concentration (optimal group—ODG, suboptimal group—SDG), second, according to drops in 25(OH)D concentration (high drop group—HDG, low drop group—LDG). A significant decrease (p < 0.001) in the 25(OH)D concentration was reported in the total group (TGr) and in all subgroups. Blood parameters such as white blood cells, red blood cells, haemoglobin and haematocrit increased significantly (p < 0.05) in TGr during the analysed period of time. The analysis of changes in the lipid profile did not expose significant differences except triglycerides. The asparagine amino transferase and creatine kinase activity decreased significantly after autumn in all analysed groups. The declining level of 25(OH)D concentration should be compensated (e.g., with vitamin D supplementation) during autumn. Applied training loads could also influence the blood parameters variability in young soccer players. Regular measurements of 25(OH)D concentration are helpful in identifying potential drops and allows for the preparation of individual supplementation plans for the players.

Background: The aim of the study was to demonstrate changes in 25(OH)D concentration, bone resorption indicators and physical fitness in female handball players as a result of their exposure to the sun, diet and exercise load during the six-month training period from mid-March to mid-September, i.e. the time when the sun exposure is the highest during the calendar year. Twenty-two women handball players participated in the study. Due to the random occurrences and exclusion criteria, 20 players completed the project. Biochemical analysis of blood, aerobic capacity, running speed and power tests (Wingate test, squat jump, counter movement jump, etc.) was conducted three times during this six-month period. Significant changes in 25(OH)D, PTH concentrations and some physical tests were demonstrated between all the tested moments. A very strong effect size has been found for almost all the indicators, except PTH, which presents a smaller value. No direct correlation was found between 25(OH)D levels and performance.