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Umarov Jamshid, researcher, Uzbek State University of Physical Education and Sport, Tashkent, Uzbekistan
Kerimov Fikrat, professor, Uzbek State University of Physical Education and Sport, Tashkent, Uzbekistan Toychiev Abdurakhim, researcher, Research Institute of Epidemiology, Microbiology and Infectious Diseases, Tashkent, Uzbekistan
Davis Nikolay,
researcher, Research Institute of Epidemiology, Microbiology and Infectious Diseases, Tashkent, Uzbekistan
Osipova Svetlana,
senior researcher, Research Institute of Epidemiology, Microbiology and Infectious Diseases, Tashkent, Uzbekistan E-mail: davisnikolay@gmail.com
VITAMIN D LEVEL AMONG ELITE WRESTLERS IN UZBEKISTAN
Abstract: The purpose of the study is to determine vitamin D levels and acute upper respiratory tract infections morbidity among elite wrestlers in Uzbekistan as well as possible association with overtraining syndrome. The study shows vitamin D deficiency/insufficiency is widely spread both in elite wrestlers and population in Uzbekistan. Monitoring of vitamin D level in elite athletes with subsequent correction is necessary. Vitamin D deficiency/insufficiency in athletes correlates with high morbidity with URI and could be associated with OS. Keywords: vitamin D, elite wrestlers, cytokines, acute respiratory infections.
Introduction
Athletes are at risk for injuries and their prevention and rehabilitation are aspects of great importance. Upper respiratory acute infections (URI) are the most common reason for non-injury-related presentation to sports medicine clinics, accounting for 35-65% of illness presentations. URI can have a negative impact on the health and performance of athletes undertaking high levels of strenuous exercise. The cause of upper respiratory symptoms in athletes can be uncertain, but the majority of cases are related to common respiratory viruses, viral reactivation, allergic responses to aeroallergens and exercise-related trauma to the integrity of respiratory epithelial membranes. Bacterial respiratory infections are less common in athletes [1]. Elite athletes are at a greater risk for injuries and URI; during the Olympic Games in 2016 (Rio de Janeiro), medical staff reported 9.8% injuries and 5.4% illnesses. Of the illnesses, 47% affected the respiratory system and 21% the gastrointestinal system [2]. Another important problem in sport is overtraining syndrome (OS). Etiology of OS remains unclear and the term "unexplained underperfor-mance syndrome" adopted in UK [3] seems to be more justified, because it emphasizes the complexity of the syndrome and its multifactorial etiology [4].
Above mentioned problems are connected or could be connected with vitamin D (VD) deficiency/insufficiency, which is spread throughout the world, including countries subtropical and tropical countries [5; 6]. VD deficiency is common in athletes. For athletes presenting with stress fractures, musculoskeletal pain, and frequent illness, one should have a heightened awareness of the additional likely diagnosis of VD deficiency. Correction of the deficiency is completed by standardized and supervised oral supplementation protocols producing significant musculoskeletal sports health benefits [7]. VD influences the musculoskeletal health and mineral homeostasis. A serum level > 30 ng/ml provides sufficient mineralization of non-mineralized bone matrix and positively correlated with an accelerated regeneration of muscular force. Levels above 40 ng/ml provided a protective effect on the development of stress fractures. Levels above 50 ng/ml are required for athletes to achieve maximal physical performance [8].
VD deficiency/insufficiency correlated with a high frequency and severe course of URI (Owens et al. 2018). VD supplementation is considered as a safe and inexpensive method for URI prevention [9; 10]. This effect can be due to the capacity of VD to increase expression of antimicrobial proteins, in particular cathelicidin in macrophages [11].
Evaluation of the VD deficiency/insufficiency prevalence among athletes as well as among population has not been carried out in Uzbekistan previously.
The purpose of the study is to determine VD levels and URI morbidity among elite wrestlers in Uzbekistan as well as the possible association with OS.
Materials and methods
The prospective diagnostic study was conducted on the basis of the Uzbek State University of Physical Education and Sport and Research Institute of Epidemiology, Microbiology and Infectious Diseases, Tashkent, Uzbekistan during the period from January 2017 till January 2018.
Study participants included 40 elite athletes engaged in freestyle and Greco-Roman wrestling (all males) at the age of 19-24 years. The control group (n = 60) for comparison ofVD and cytokines level included healthy individuals of the same sex and age without expressed manifestations of diseases. All the participants were residents of Uzbekistan. Participants were required to complete a comprehensive health screening questionnaire, paying special attention to the number of and medical examination prior to starting the study. Participants could be included if they were currently healthy (with no health problems or infection symptoms within the previous two weeks), engaged in regular sports training at least six months and at least 3 h of total moderate/high-intensity training time per week.
Immunological tests. Participants were required to abstain from any strenuous physical activity for 24 h before coming to the laboratory. Five milliliters of peripheral venous blood was taken (after 8-12 hours of fasting) from each participant and were collected into Human Tube Serum Gel - C/A for ELISA. All blood samples were collected in August and January. Serum levels of 25(OH) VD and TNF-a, IFN-y and IL-4 were detected by ELISA technique using DIAsource kit, Belgium and LLC kit, Vector-Best, Novosibirsk, Russia respectively.
Table 1
Classification of the level ofVD. Serum VD level was classified as reported by Holick et al. [12]. Levels of VD < 20, 21-29, > 30-150, and > 150 ng/ml were considered as VD deficiency, VD insufficiency, VD sufficiency and VD intoxication, respectively.
The performers of immunological tests did not have access to any information about an individual under examination. All information was blinded.
Frequency of URI was detected by answers of athletes and coaches as well as participants of the control group in questionnaires to the question "the number of URI episodes in summer-autumn and winter-spring".
Previously, authors [13] examining junior wresters showed that intestinal parasites can imitate OS due to the rather high frequency of astenoneurotic syndrome manifesting by the symptoms typical for OS: irritability, mood swings, increased fatigability, performance decrement, sleep disturbances anorexia, etc. So all the athletes were examined for intestinal parasites by triple coproscopy, stool samples were taken with 1-3 days interval.
Statistical analysis. Data analysis was performed with the program Origin 6.1 (OriginLab, Northampton, MA). Results are expressed as mean ± standard error (SEM) for continuous variables and number (percentage) for categorical data. For numerical variables the independent/paired t test were used. The P value < 0.05 was considered as statistically significant.
Results
Table 1 demonstrates that in both groups vitamin D deficiency/insufficiency was prevalent. Frequency of VD deficiency was higher in both groups in winter and VD sufficiency among athletes was not detected in winter. The number of individuals with VD sufficiency was higher in population, but
even in summer this index amounted to only 30%.
The level of serum 25(OH) VD in wrestlers (n = 40) and the control individuals (n = 60) in August and January
25(OH) VD level in blood serum The percentage of participants with VD sufficiency/insufficiency/deficiency no. (%)
Wrestlers (n = 40) Control individuals (n = 60)
August January August January
Sufficiency (> 30 ng/ml) 4(10) abs 18(30) 6(10)
Insufficiency (20-29 ng/ml) 32(80) 28(70) 36(60) 42(70).
Deficiency (< 20 ng/ml) 4(10) 12(30) 6(10) 12(20)
Table 2 shows a significant elevation of TNF-a in the nificantly decreased, the lowest value was obtained in athletes athletes with VD deficiency, which is a biomarker of inflam- with VD deficiency. Changes in the level of anti-inflammatory mation. The level of proinflammatory cytokine IFN-y was sig- IL-4 were less expressed.
Table 2.- The level of serum cytokines in elite wrestlers with various level of serum VD
Cohort under study TNF-a pg/ml IFN-y Pg/ml IL-4 Pg/ml
Athletes with VD deficiency (n = 5) 31 ± 11.9* 5.9 ± 2.9* 4.3 ± 1.8
Athletes with VD insufficiency (n = 10) 22 ± 7.1* 8.1 ± 3.2* 5.1 ± 2.2
Athletes with VD sufficiency (n = 3) 9 ± 15 10 ± 12 2 ± 4
Control individuals (n = 12) 4.1 ± 2.7 17.9 ± 3.1 3.5 ± 1.9
* - significant difference with the control individuals (P < 0.05)
Table 3 shows the frequency of URI during summer-autumn and winter-spring periods among athletes and the control individuals. In both groups URI episodes were observed more frequently in winter-spring period. However, more than 5 episodes of URI were detected only in elite athletes in
winter-spring. 3-4 episodes of URTI regardless of the season were significantly more frequently detected in wrestlers in comparison with the control individuals (P < 0.05).Absence of URI was observed in a very low percentage of elite athletes versus the control individuals.
Table 3.- The frequency of URI during summer-autumn (sum-aut) and winter-spring (win-spr) periods among athletes and the control individuals
The number of episodes of URI The frequency of URI among participants (%) during summer-autumn and winter-spring periods no. (%)
Wrestlers(n = 40) Control individuals (n=60)
sum-aut win-spr sum-aut win-spr
Absence of URI 15(37.5) - 55(91.6) 24 (41.1)
<2 episodes 25(62.5) 5(12.5) 5(8.3) 20 (33.3)
3-4 episodes - 34(85) 6 (16.6)
>5 episodes - 1(2.5)
* - significant difference with the control individuals (P < 00
All wrestlers were examined for symptoms typical for OS (absence of sport enthusiasm, mood swings, problems with concentration, sleep disturbances, increased fatigabil-
ity, anorexia, reduced performance, increased morbidity, injury frequency etc. [14] and infections, including intestinal parasites, because previously we found that intestinal parasitic diseases can imitate OS [13]. Study was performed in January. These symptoms were identified in 14 wrestlers. They were examined for infections, including intestinal parasites. Intestinal parasites (Ascaris lumbricoides, Enterobius vermicu-laris and Giardia lamblia were found in 8 athletes and after treatment and elimination of parasites symptoms typical for OS disappeared in 6 athletes without any changes in training conditions. Symptoms of OS were persisted in 6 athletes free of infection. VD deficiency was revealed in of them, VD insufficiency was diagnosed in one athlete.
Discussion
Prevalence ofVD deficiency/insufficiency was determined in athletes as well as in population (in 90% and 70% of examined individuals, respectively). These values were obtained in summer. The number of individuals with VD sufficiency was higher in population, but even in summer this index amounted
to only 30%, in spite of the abundance of sunny days in the year (> 300 days a year), dropping to 10% in winter.
These results were unexpected to some extent, but they were in accordance with data of Shuler et al. [8], that VD deficiency is common in athletes and the incidence of VD deficiency in elite indoor athletes is up to 94%, moreover VD insufficiency can be considered as epidemic in population also.
Significant increase of serum TNF-a concentration was observed in the athletes, it was especially expressed in athletes with VD deficiency. Our results are in agreement with data of Willis et al. [15] on correlation of VD insufficiency with elevated level of TNF-a. Decrease in serum INF-y concentration was observed. Thus, the dynamics of the cytokines level in deficiency/insufficiency and sufficiency ofVD indicates the effect of VD on the immune system. In particular, reduction of IFN-y increases susceptibility to URI [16]. The number of athletes with VD sufficiency was too small, but it is obvious that IFN-y level is significantly lower than that in healthy individuals, apparently due to a significant physical load.
Frequency of URI episodes was much higher in wrestlers than in the control individuals independently on the season, among other factors it could be specified by low IFN-y level,
which is connected with elevated susceptibility to URI [17] and other factors, including suppression of immune system associated with lower VD level and intensive physical load.
Pathophysiology of the OS has not been determined yet. Cytokine hypothesis seems to be close to reality, because the pro-inflammatory cytokines IL-1b and TNF-a affect the brain, causing a decrease in appetite, sleep disturbance and depression, cytokines can act directly on the central receptors or activate the axis hypothalamus-pituitary-adrenal glands, releasing stress hormones, which leads to the same effect [7]. There is evidence of an increase in the level of these cytokines in patients with depression [18]. Thus, VD deficiency can impose OS manifestation.
Efficiency of the training process is ensured by an adequate balance of training load and recovery. OS can be developed in excessive muscle loading and additional stresses as well as concomitant diseases. 6 athletes with persisting OS symptoms were free of infections including intestinal parasites, but were characterized with VD deficiency in 5 cases and in 1 case by VD insufficiency. We assumed that OS can be connected with VD deficiency/insufficiency. This assumption is supported by Sedaghat et al. [19] who established in
experiments on animals subjected to chronic stress that VD (1.25-(OH)2VD3) improved the condition of animals, eliminating the main symptoms of stress, which can be interpreted as an indication the role ofVD in the OS development.
Conclusion
VD deficiency/insufficiency is widely spread both in elite wrestlers and population in Uzbekistan. Monitoring of VD level in elite athletes with subsequent correction is necessary. VD deficiency/insufficiency in athletes correlates with high morbidity with URI. VD deficiency/insufficiency could be associated with OS.
Disclosure of interest
The authors report no conflict of interest. The project was supported by a research grant from the Ministry of Innova-tional Development of the Republic of Uzbekistan.
Ethics approval
The study was approved by the Medical Ethics Committee of the Ministry of Health of the Republic of Uzbekistan in accordance with the Declaration of Helsinki. All participants were fully informed about the rationale for the study. Both informed and written consents were obtained from athletes and the control individuals.
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