Associations of Vitamin D Levels with Physical Fitness and Motor Performance; A Cross-Sectional Study in Youth Soccer Players from Southern Croatia

Simple Summary Vitamin D is a fat-soluble prohormone crucial for bone mineralization, muscle contractility, and neurological conductivity. It is theorized that Vitamin D plays an important role in sport performances, especially in young athletes. In this study we examined the associations of levels of 25-hydroxyvitamin D (25(OH)D) with physical fitness and motor-performance achievements in youth soccer players from Southern Croatia. Participants were tested on physical fitness, motor performance and vitamin D at the end of the winter period, when levels of vitamin D are known to be lowest due to low exposure to sunlight. Results showed that deficiency of 25(OH)D was widespread among youth soccer players living in Southern Croatia. Low 25(OH)D levels were associated with lower results in fitness tests (i.e., tests of energetic capacities), but there was no correlation between 25(OH)D levels and the results in motor performance tests (i.e., skill tests). Our results support the theory of the association between vitamin D and energetic capacities of athletes, but there is no evidence on association between vitamin D and skill-based capacities. Vitamin D level is known to be a factor potentially influencing physical fitness, but few studies have examined this phenomenon among youth athletes. We aimed to evaluate the associations of vitamin D levels (as measured by 25-hydroxyvitamin D concentrations-25(OH)D) with various physical fitness and motor performance tests in youth football (soccer) players. This cross-sectional study included a total of 52 youth soccer players (15.98 +/- 2.26 years old) from Southern Croatia. The participants were evaluated at the end of the winter period and data were collected of anthropometric measures (body mass and body height), vitamin D status (25(OH)D levels), physical fitness tests (sprints of 10 and 20 m, 20 yards test, the countermovement jump, the reactive strength index (RSI)) and motor performance tests (the soccer-specific CODS, the soccer-specific agility, and static balance). Among the studied players, 54% had 25(OH)D insufficiency/deficiency, showing a lack of 25(OH)D is widespread even in youth athletes living at a southern latitude. The 25(OH)D level was correlated with sprint 20 m, 20 yards tests, and RSI, showing a greater role of 25(OH)D in physical fitness tests where energetic capacity is essential than in sport-related motor performance tests where skills are crucial. Our results support the idea that vitamin D can play a determinant role in physical fitness tests with a clear physiological component, but is not crucial in motor performance tests related to specific sports where skills are a key component. Future studies should investigate the effects of vitamin D supplementation on the performance in physical fitness and motor performance tests among youth athletes.This research is partially financed by Croatian Science Foundation (grant numbers: IP2018-01-8330; DOK-2018-09-1940)

VITAMIN D AND PHYSICAL PERFORMANCE OF YOUNG ATHLETES

Cilj istraživanja: Cilj ovog istraživanja bio je utvrditi povezanost koncentracije vitamina D i kondicijskih kapaciteta u mladih nogometaša. Materijali i metode: Ovo presječno istraživanje je uključilo 52 mlada nogometaša (u dobi od 15,98±2,26 godina) iz Splita. Prikupljanje svih podataka o ispitanicima je obavljeno tijekom veljače 2019. godine. Uključene varijable bile su koncentracija 25(OH)D-a, test sprinta na 10 i 20 metara, test skoka s pripremom, indeks reaktivne snage, test brzine promjene smjera specifičan za nogomet, test reaktivne agilnosti specifičan za nogomet te indeksi statičke i dinamičke ravnoteže. Rezultati: Primjerena razina vitamina D je nađena u 23 (44%) ispitanika, a 29 (56%) ispitanika je imalo niske razine vitamina D. Od toga je deficijencija vitamina D pronađena u 4 (8%), a insuficijencija vitamina D u 25 (48%) ispitanika. Prosječna koncentracija vitamina D u ovom istraživanju iznosila je 79,03 nmol/L (SD= 25,32). Korelacija na razini statističke značajnosti (P<0,05) utvrđena je za test sprinta na 20 metara (r=-0,29), test 20 jardi (r=-0,31) i indeks reaktivne snage (r=-0,32), a nije bilo statistički značajne korelacije između razine 25(OH)D-a i ostalih sportskih testova. Zatim je izvršena analiza za subuzorke ispitanika. Vitamin D suficijentna skupina je imala statistički značajno bolje rezultate u testovima sprinta na 20 m (3,06±0,18 s vs. 3,19±0,2 s; P=0,02), 20 jardi (4,74±0,27 s vs. 4,95±0,4 s; P=0,04) i indeksu reaktivne snage (151,07±34,35 m/s vs. 131,12±31,13 m/s; P=0,03) u odnosu na skupinu s insuficijencijom/deficijencijom vitamina D. Nisu pronađene statistički značajne razlike između skupina u ostalim testovima. Zaključak: Čak 56% mladih sportaša imalo je nisku razinu vitamina D. Pronađena je povezanost serumske razine 25(OH)D-a i testova sprinta na 20 metara, 20 jardi i indeksa reaktivne snage, a nije bilo povezanosti između razine 25(OH)D-a i ostalih testova. Dobiveni rezultati ukazuju na moguću potpornu ulogu vitamina D u sportskoj izvedbi. To, međutim, ne umanjuje njegovu važnost jer na elitnoj sportskoj razini male promjene u izvedbi mogu odrediti ishod natjecanja. Potrebne su dodatne eksperimentalne studije koje bi proučile uzročnoposljedičnu vezu između statusa vitamina D i kondicijskih kapaciteta sportaša.Objectives: The aim of the presented study was to determine the relationship between vitamin D concentrations and physical performance in young football players. Materials and methods: This cross-sectional study included 52 young football players (age: 15.98±2.26 years) from Split. The data was collected during February 2019. Included variables were serum 25(OH)D concentrations, 10m and 20m sprint, countermovement jump, reactive strength index, football-specific change of direction, football-specific reactive agility, overall stability index and limits of stability balance test. Results: Adequate vitamin D levels were given in 23 (44%) subjects and 29 (56%) subjects had low vitamin D levels. Vitamin D deficiency has been demonstrated among 4 (8%) and vitamin D insufficiency among 25 (48%) subjects. Mean serum vitamin D concentrations for all participants was 79.03 nmol/L (SD = 25.32). Correlation at the level of statistical significance (P<0.05) was determined for 20m sprint test (r=-0.29), 20 yards test (r=-0.31) and reactive strength index (r=-0.32), while there were no statistically significant correlation between 25(OH)D concentration and other tests. Vitamin D sufficient group had statistically better results in 20m sprint test (3.06±0.18 s versus 3.19±0.2 s; P = 0.02), 20 yards test (4.74±0.27 s versus 4.95±0.4 s; P = 0.04) and reactive strength indeks (151.07±34.35 m/s versus 131.12±31.13 m/s; P = 0.03) in relation to the vitamin D insufficient/deficient group. In other tests, there were no statistically significant differences between groups. Conclusion: As many as 56% of young athletes had low vitamin D concentration. The obtained results indicate the possibility of a supportive role of vitamin D in athletic performance. However, this did not diminish importance of vitamin D because at the elite athletic level even slight improvement in performance makes a difference. Additional experimental studies are needed to study the consequential relationship between vitamin D status and physical performance

VITAMIN D AND PHYSICAL PERFORMANCE OF YOUNG ATHLETES

Cilj istraživanja: Cilj ovog istraživanja bio je utvrditi povezanost koncentracije vitamina D i kondicijskih kapaciteta u mladih nogometaša. Materijali i metode: Ovo presječno istraživanje je uključilo 52 mlada nogometaša (u dobi od 15,98±2,26 godina) iz Splita. Prikupljanje svih podataka o ispitanicima je obavljeno tijekom veljače 2019. godine. Uključene varijable bile su koncentracija 25(OH)D-a, test sprinta na 10 i 20 metara, test skoka s pripremom, indeks reaktivne snage, test brzine promjene smjera specifičan za nogomet, test reaktivne agilnosti specifičan za nogomet te indeksi statičke i dinamičke ravnoteže. Rezultati: Primjerena razina vitamina D je nađena u 23 (44%) ispitanika, a 29 (56%) ispitanika je imalo niske razine vitamina D. Od toga je deficijencija vitamina D pronađena u 4 (8%), a insuficijencija vitamina D u 25 (48%) ispitanika. Prosječna koncentracija vitamina D u ovom istraživanju iznosila je 79,03 nmol/L (SD= 25,32). Korelacija na razini statističke značajnosti (P<0,05) utvrđena je za test sprinta na 20 metara (r=-0,29), test 20 jardi (r=-0,31) i indeks reaktivne snage (r=-0,32), a nije bilo statistički značajne korelacije između razine 25(OH)D-a i ostalih sportskih testova. Zatim je izvršena analiza za subuzorke ispitanika. Vitamin D suficijentna skupina je imala statistički značajno bolje rezultate u testovima sprinta na 20 m (3,06±0,18 s vs. 3,19±0,2 s; P=0,02), 20 jardi (4,74±0,27 s vs. 4,95±0,4 s; P=0,04) i indeksu reaktivne snage (151,07±34,35 m/s vs. 131,12±31,13 m/s; P=0,03) u odnosu na skupinu s insuficijencijom/deficijencijom vitamina D. Nisu pronađene statistički značajne razlike između skupina u ostalim testovima. Zaključak: Čak 56% mladih sportaša imalo je nisku razinu vitamina D. Pronađena je povezanost serumske razine 25(OH)D-a i testova sprinta na 20 metara, 20 jardi i indeksa reaktivne snage, a nije bilo povezanosti između razine 25(OH)D-a i ostalih testova. Dobiveni rezultati ukazuju na moguću potpornu ulogu vitamina D u sportskoj izvedbi. To, međutim, ne umanjuje njegovu važnost jer na elitnoj sportskoj razini male promjene u izvedbi mogu odrediti ishod natjecanja. Potrebne su dodatne eksperimentalne studije koje bi proučile uzročnoposljedičnu vezu između statusa vitamina D i kondicijskih kapaciteta sportaša.Objectives: The aim of the presented study was to determine the relationship between vitamin D concentrations and physical performance in young football players. Materials and methods: This cross-sectional study included 52 young football players (age: 15.98±2.26 years) from Split. The data was collected during February 2019. Included variables were serum 25(OH)D concentrations, 10m and 20m sprint, countermovement jump, reactive strength index, football-specific change of direction, football-specific reactive agility, overall stability index and limits of stability balance test. Results: Adequate vitamin D levels were given in 23 (44%) subjects and 29 (56%) subjects had low vitamin D levels. Vitamin D deficiency has been demonstrated among 4 (8%) and vitamin D insufficiency among 25 (48%) subjects. Mean serum vitamin D concentrations for all participants was 79.03 nmol/L (SD = 25.32). Correlation at the level of statistical significance (P<0.05) was determined for 20m sprint test (r=-0.29), 20 yards test (r=-0.31) and reactive strength index (r=-0.32), while there were no statistically significant correlation between 25(OH)D concentration and other tests. Vitamin D sufficient group had statistically better results in 20m sprint test (3.06±0.18 s versus 3.19±0.2 s; P = 0.02), 20 yards test (4.74±0.27 s versus 4.95±0.4 s; P = 0.04) and reactive strength indeks (151.07±34.35 m/s versus 131.12±31.13 m/s; P = 0.03) in relation to the vitamin D insufficient/deficient group. In other tests, there were no statistically significant differences between groups. Conclusion: As many as 56% of young athletes had low vitamin D concentration. The obtained results indicate the possibility of a supportive role of vitamin D in athletic performance. However, this did not diminish importance of vitamin D because at the elite athletic level even slight improvement in performance makes a difference. Additional experimental studies are needed to study the consequential relationship between vitamin D status and physical performance

VITAMIN D AND PHYSICAL PERFORMANCE OF YOUNG ATHLETES

Cilj istraživanja: Cilj ovog istraživanja bio je utvrditi povezanost koncentracije vitamina D i kondicijskih kapaciteta u mladih nogometaša. Materijali i metode: Ovo presječno istraživanje je uključilo 52 mlada nogometaša (u dobi od 15,98±2,26 godina) iz Splita. Prikupljanje svih podataka o ispitanicima je obavljeno tijekom veljače 2019. godine. Uključene varijable bile su koncentracija 25(OH)D-a, test sprinta na 10 i 20 metara, test skoka s pripremom, indeks reaktivne snage, test brzine promjene smjera specifičan za nogomet, test reaktivne agilnosti specifičan za nogomet te indeksi statičke i dinamičke ravnoteže. Rezultati: Primjerena razina vitamina D je nađena u 23 (44%) ispitanika, a 29 (56%) ispitanika je imalo niske razine vitamina D. Od toga je deficijencija vitamina D pronađena u 4 (8%), a insuficijencija vitamina D u 25 (48%) ispitanika. Prosječna koncentracija vitamina D u ovom istraživanju iznosila je 79,03 nmol/L (SD= 25,32). Korelacija na razini statističke značajnosti (P<0,05) utvrđena je za test sprinta na 20 metara (r=-0,29), test 20 jardi (r=-0,31) i indeks reaktivne snage (r=-0,32), a nije bilo statistički značajne korelacije između razine 25(OH)D-a i ostalih sportskih testova. Zatim je izvršena analiza za subuzorke ispitanika. Vitamin D suficijentna skupina je imala statistički značajno bolje rezultate u testovima sprinta na 20 m (3,06±0,18 s vs. 3,19±0,2 s; P=0,02), 20 jardi (4,74±0,27 s vs. 4,95±0,4 s; P=0,04) i indeksu reaktivne snage (151,07±34,35 m/s vs. 131,12±31,13 m/s; P=0,03) u odnosu na skupinu s insuficijencijom/deficijencijom vitamina D. Nisu pronađene statistički značajne razlike između skupina u ostalim testovima. Zaključak: Čak 56% mladih sportaša imalo je nisku razinu vitamina D. Pronađena je povezanost serumske razine 25(OH)D-a i testova sprinta na 20 metara, 20 jardi i indeksa reaktivne snage, a nije bilo povezanosti između razine 25(OH)D-a i ostalih testova. Dobiveni rezultati ukazuju na moguću potpornu ulogu vitamina D u sportskoj izvedbi. To, međutim, ne umanjuje njegovu važnost jer na elitnoj sportskoj razini male promjene u izvedbi mogu odrediti ishod natjecanja. Potrebne su dodatne eksperimentalne studije koje bi proučile uzročnoposljedičnu vezu između statusa vitamina D i kondicijskih kapaciteta sportaša.Objectives: The aim of the presented study was to determine the relationship between vitamin D concentrations and physical performance in young football players. Materials and methods: This cross-sectional study included 52 young football players (age: 15.98±2.26 years) from Split. The data was collected during February 2019. Included variables were serum 25(OH)D concentrations, 10m and 20m sprint, countermovement jump, reactive strength index, football-specific change of direction, football-specific reactive agility, overall stability index and limits of stability balance test. Results: Adequate vitamin D levels were given in 23 (44%) subjects and 29 (56%) subjects had low vitamin D levels. Vitamin D deficiency has been demonstrated among 4 (8%) and vitamin D insufficiency among 25 (48%) subjects. Mean serum vitamin D concentrations for all participants was 79.03 nmol/L (SD = 25.32). Correlation at the level of statistical significance (P<0.05) was determined for 20m sprint test (r=-0.29), 20 yards test (r=-0.31) and reactive strength index (r=-0.32), while there were no statistically significant correlation between 25(OH)D concentration and other tests. Vitamin D sufficient group had statistically better results in 20m sprint test (3.06±0.18 s versus 3.19±0.2 s; P = 0.02), 20 yards test (4.74±0.27 s versus 4.95±0.4 s; P = 0.04) and reactive strength indeks (151.07±34.35 m/s versus 131.12±31.13 m/s; P = 0.03) in relation to the vitamin D insufficient/deficient group. In other tests, there were no statistically significant differences between groups. Conclusion: As many as 56% of young athletes had low vitamin D concentration. The obtained results indicate the possibility of a supportive role of vitamin D in athletic performance. However, this did not diminish importance of vitamin D because at the elite athletic level even slight improvement in performance makes a difference. Additional experimental studies are needed to study the consequential relationship between vitamin D status and physical performance