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Gal Dubnov and Naama W. Constantini

Iron depletion, with or without anemia, may have a negative effect on physical and mental performance. Even with current recognition of the problem, its incidence among athletes remains high. Most studies describe iron status in endurance athletes. This study examined the prevalence of iron depletion and anemia among male and female top-level basketball players. Adolescents and adults (N = 103) from 8 national basketball teams were screened for anemia and iron stores status, which included a complete blood count and levels of plasma ferritin, transferrin, and serum iron. Iron depletion, defined by a ferritin level below 20 μg/L, was found among 22% of study participants (15% in males vs. 35% in females, p = .019). Anemia was found among 25% of athletes (18% in males vs. 38% in females, p = .028). Iron deficiency anemia, defined by the presence of anemia, ferritin levels below 12 μg/L, and transferrin saturation below 16%, was found among 7% of players (3% in males vs. 14% in females, p = .043). In summary, a high prevalence of iron depletion, anemia, and iron deficiency anemia was found among basketball players of both genders. We recommend screening ballgame players for blood count and iron store status, and providing nutritional counseling and iron supplementation when necessary.

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Gal Dubnov-Raz, Netachen Livne, Raanan Raz, Avner H. Cohen, and Naama W. Constantini

It is hypothesized that vitamin D insufficiency in athletes might negatively affect sport performance. The objective of this study was to examine the effect of vitamin D3 supplementation on physical performance of adolescent swimmers with vitamin D insufficiency. Fifty-three adolescent competitive swimmers with vitamin D insufficiency (serum 25-hydroxyvitamin-D concentrations (25(OH)D)<30ng/ml, mean 24.2 ± 4.8ng/ml) were randomized to receive 2,000IU/day of vitamin D3 or placebo for 12 weeks. Swimming performance at several speeds, arm-grip strength, and one-legged balance, were measured before and after supplementation. The age-adjusted changes in performance variables during the study were compared between groups. 25(OH) D concentrations at study end were significantly higher in the vitamin group compared with the placebo group (29.6 ± 6.5ng/ml vs. 20.3 ± 4.2ng/ml, p < .001), yet only 48% of the vitamin group became vitamin D sufficient with this dosing. No between-group differences were found in the changes of the performance variables tested. No significant differences in performance were found between participants that became vitamin D sufficient, and those who did not. No significant correlation was found between the change in serum 25(OH)D and ageadjusted balance, strength or swimming performance at study end. Vitamin D3 supplementation that raised serum 25(OH)D concentrations by a mean of 9.3ng/ml above placebo in adolescent swimmers with vitamin D insufficiency, did not improve physical performance more than placebo.

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Gal Dubnov-Raz, Netachen Livne, Raanan Raz, Daniel Rogel, Avner H. Cohen, and Naama W. Constantini

Serum vitamin D concentrations (25[OH]D) are associated with physical performance in the general population, but few studies have been published in athletes. 80 competitive adolescent swimmers from both sexes were tested for serum 25(OH)D concentrations, grip strength, balance and swimming performance at several speeds. Spearman’s correlations were used to examine the associations between 25(OH)D concentrations and age-adjusted measures of performance. Performance parameters were also compared between vitamin D sufficient (n = 27), insufficient (25[OH]D ranging 20−29.9 ng/ml, n = 42), and deficient (25[OH]D < 20 ng/ml, n = 11) participants. No significant associations were found between serum 25(OH)D concentrations and any of the performance measures, with no significant differences found between vitamin D sufficient, insufficient and deficient participants. In competitive adolescent swimmers, serum vitamin D concentrations were not associated with strength, balance or swimming performance. Vitamin D insufficient/deficient swimmers did not have reduced performance.

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Gal Dubnov-Raz, Harri Hemilä, Avner H. Cohen, Barak Rinat, Lauryn Choleva, and Naama W. Constantini

Observational studies identified associations between vitamin D insufficiency (serum 25(OH)D > 30ng·ml−1) and risk of upper respiratory infection (URI). Swimmers are highly prone to URIs, which might hinder their performance. The aim of this study was to examine if vitamin D3 supplementation reduces URI burden in vitamin D-insufficient swimmers. Fifty-five competitive adolescent swimmers with vitamin D insufficiency were randomized to receive vitamin D3 (2,000IU·d4) or placebo for 12 winter weeks. A URI symptom questionnaire was completed weekly. Serum 25(OH)D concentrations were measured by radio-immunoassay before and after supplementation. We used linear regression to examine the relation between the change in 25(OH)D concentrations during the trial, and the duration and severity of URIs. There were no between-group differences in the frequency, severity, or duration of URIs. Exploratory analyses revealed that in the placebo group only, the change in 25(OH)D concentrations during the trial was highly associated with the duration of URIs (r = −0.90,p > .001), and moderately associated with the severity of URIs (r = −0.65,p = .043). The between-group differences for duration were highly significant. Vitamin D3 supplementation in adolescent swimmers with vitamin D insufficiency did not reduce URI burden. However, larger decreases in serum 25(OH)D concentrations were associated with significantly longer and more severe URI episodes.

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Naama W. Constantini, Alon Eliakim, Levana Zigel, Michal Yaaron, and Bareket Falk

Much attention has focused on the nutrition and hematological profile of female athletes, especially gymnasts. The few studies on iron status of male adolescent athletes found a low incidence of iron deficiency. The present study investigated the iron status of male and female gymnasts (G) and compared it with athletes of other sports. Subjects were 68 elite athletes (43 M, 25 F) ages 12-18, of four sports: gymnasts (11 M, 12 F), swimmers (11 M, 6 F), tennis players (10 M, 4 F), and table tennis players (11 M, 3 F). All lived in the national center for gifted athletes, trained over 25 hr a week, ate in the same dining room, and shared a similar lifestyle. Mean levels of hemoglobin (Hb), red blood cell indexes, serum ferritin, serum iron, and transferrin were measured in venous blood. There was no difference in mean Rb among gymnasts (G) and nongymnasts (NG). However, Hb was less than 14 g/dL in 45% of M G vs. only 25% in NG, and less than 13 g/dL in 25% of premenarcheal FG vs. 15% in NG. Low transferrin saturation (< 20%) was detected in 18% of M G and 25% of FG vs. 6% and 8% in male and female NG, respectively (p < .05). The percentage of males suffering from low ferritin level (< 20 ng/ml) was twice as high in G (36%) vs. NG (19%), and about 30% in all females. In summary, iron stores were consistently lower in M G vs. NG. Adolescent athletes of both genders, G in particular, are prone to nonanemic iron deficiency, which might compromise their health and athletic performance.