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OVERTRAINING IN ATHLETES

Overtraining in athletes bears many similarities to hyperthyroidism.  In fact many elite athletes, especially females, develop hyperthyroidism.  Iron deficiency seems to be a core mineral deficiency in overtraining.

Clin Hemorheol Microcirc 1998 Jul;18(4):309-18

Increased blood viscosity in iron-depleted elite athletes.

Khaled S, Brun JF, Wagner A, Mercier J, Bringer J, Prefaut C

Service d'Exploration Physiologique des Hormones et des Metabolismes, CHRU de Montpellier, France.

Since iron deficiency is associated with abnormal erythrocyte rheology, we investigated relationships between plasma ferritin and blood rheology in 36 male elite sportsmen (age: 22.38+/-0.9 years). On the whole, ferritin was negatively correlated with blood viscosity (r = -0.36, p < 0.05). When 23 subjects with low ferritin levels suggesting mild iron deficiency were compared with 13 matched sportsmen with normal ferritin levels, iron-deficient sportsmen were shown to have a higher blood viscosity at 1000 s(-l) (3.17+/-0.09 vs. 2.85+/-0.06 mPas, p < 0.05), explained by a higher plasma viscosity (1.38+/-0.02 vs. 1.31+/-0.02 mPa s, p < 0.05), while hematocrit and RBC rigidity index Tk were similar in the two groups. RBC aggregability index M (4.59+/-0.58 vs. 2.95+/-0.43 mPas, p < 0.05) and M1 (8.46+/-0.58 vs. 6.07+/-0.55, p < 0.01) were higher in iron-deficient subjects. Serum zinc was lower in iron-deficient sportsmen (0.73+/-0.02 vs. 0.83+/-0.02 mg/l, p < 0.01), but the score of early signs of overtraining was higher in this group (10.84+/-1.61 vs. 4.08+/-1.11, p < 0.01). These data suggest that mild iron deficiency as commonly seen in athletes, before anemia occurs, is associated with an increase in plasma viscosity and RBC aggregation, together with an increased subjective feeling of exercise overload.

 

J Sports Sci 1991 Summer;9 Spec No:91-116

Minerals: exercise performance and supplementation in athletes.

Clarkson PM

Department of Exercise Science, University of Massachusetts, Amherst 01003.

This paper examines whether mineral supplements are necessary for athletes, and whether these supplements will enhance performance. Macrominerals (calcium, magnesium, and phosphorus) and trace minerals (zinc, copper, selenium, chromium, and iron) are described. Calcium supplements are important for the health of bones. Athletes tend to have enhanced calcium status as assessed by bone mineral density, with the notable exception of female amenorrhoeic athletes. Magnesium status is adequate for most athletes, and there is no evidence that magnesium supplements can enhance performance. Phosphorus status is adequate for athletes. Phosphorus supplementation over an extended period of time can result in lowered blood calcium, however, some studies have shown that acute 'phosphate loading' will enhance performance. Athletes may have a zinc deficiency induced by poor diet and loss of zinc in sweat and urine. Limited data exist on the relationship of performance and zinc status. Widespread deficiencies in copper have not been documented, and there are no data to suggest that copper supplementation will enhance performance. There is no reason to suspect a selenium deficiency in athletes. The relationship between selenium status and performance has not been established, but selenium may play a role as an antioxidant. Because of the low intakes of chromium for the general population, there is a possibility that athletes may be deficient. Exercise may create a loss in chromium because of increased excretion into the urine. Many athletes, particularly female, are iron depleted, but true iron deficiencies are rare. Iron depletion does not affect exercise performance but iron deficiency anaemia does. Iron supplements have not been shown to enhance performance except where iron deficiency anaemia exists. In conclusion, poor diets are perhaps the main reason for any mineral deficiencies found in athletes, although in certain cases exercise could contribute to the deficiency. Mineral supplementation may be important to ensure good health, but few studies have definitively documented any beneficial effect of mineral supplementation on performance.