in physically active people, physical performance did not improve in athletes who were folate deficient and received folate supplementation. A clinically normal blood concentration of vitamin B-12 is between 200 and 900 pg/mL. Normal blood concentrations of folate range from 2.7 to 17.0 ng/mL. However, inadequate intakes of both vitamins may lead to megaloblastic anemia.1 Although injections of vitamin B-12 are used clinically for persons diagnosed with megaloblastic ane-


mia, oral supplementation is sufficient if frank anemia has not been diagnosed. A multivitamin and mineral supplement that includes 500 to 1,000 mg of vitamin C may decrease vitamin B-12 bioavailability from food and may lead to vitamin B-12 deficiency.14


Vitamin B-12 deficiency can be masked by high folate


intakes; thus, if vitamin B-12 deficiency is suspected, dietary intake will need to be assessed, especially if biochemical tests are negative for vitamin B-12 deficiency. Tese nutrients are important for vegan athletes and are discussed later in this chapter. Athletes who consume adequate amounts of vitamin B-12 and folate in their diets are probably not at


risk for vitamin B-12 or folate deficiencies. Nonetheless, vitamin B-12 or folate deficiencies can lead to increased serum homocysteine concentrations, a risk factor for cardiovascular disease.74


Normal blood


homocysteine concentrations range between 4 and 15 nmol/L, with optimal concentrations below 10 to 12 nmol/L. Te risk of hyperhomocysteinemia (>15 nmol/L) demonstrates that people who exercise need to be concerned not only about nutrition and performance but also about overall health. To conceptualize the effects of exercise intensity on homocysteine concentrations Iglesias-Gutiérrez


and colleagues studied changes in serum homocysteine concentrations in eight sedentary males during and aſter low- and high-intensity interval exercises. Teir findings indicate that high-intensity exercise raises serum homocysteine concentrations more quickly than lower-intensity exercise. Incidentally, the researchers also reported that serum concentrations of vitamin B-12, folate, and vitamin B-6 all signifi- cantly increased (P< .05) aſter both high- and low-intensity exercise.75 König and colleagues also sought to identify changes in blood homocysteine concentrations in response


to exercise. Teir findings reiterate that serum homocysteine concentrations increase in response to exer- cise; however, the timing of the alteration in concentration is not well defined.76 Herrmann and colleagues had previously explored the relationship of exercise to homocysteine con-


centrations, and, contrary to the findings of König and colleagues, he found that serum homocysteine concentrations increased during, not aſter, the bout of exercise.77


However, both researchers agreed that


homocysteine concentrations remained elevated following exercise cessation and continued to remain above normal throughout the 5-day recovery training period. Tey also found that serum vitamin B-12 concentrations were unchanged during training but decreased during the recovery phase, indicating a delayed response to the training. Serum folate concentrations, however, decreased during training but returned to normal by the end of the recovery period.76,77 Because vitamin B-12and folate are metabolically interrelated, the changes in one and not the other at


different times of exercise and recovery may indicate an adaptive response by each to protect the other. It is important for those who exercise to consume adequate amounts of vitamin B-12 and folate despite evi- dence that supplementation may only improve performance if a nutritional deficit is present.1 sources of vitamin B-12and folate are shown in Table 5.1.


Dietary


IRON Te vital role iron plays in oxygen delivery is paramount to overall exercise performance, yet iron-deficiency anemia affects one quarter of the world’s population.78


may negatively affect exercise performance. Iron-deficiency anemia negatively affects the oxidative pro- duction of adenosine triphosphate in skeletal muscle.79


anemia has been shown to decrease overall aerobic capacity and, thus, overall athletic performance79-81 Iron Supplementation: Persons with iron-deficiency depletion or anemia find that iron supplementation is the most prudent way to increase iron stores and prevent adverse physiological effects.82 fate or gluconate are the least expensive and most widely used forms of iron supplementation82,83


For athletes in particular, iron-deficiency anemia It is therefore understandable that iron-deficiency


Ferrous sul- ; however,


CHAPTER 5: VITAMINS, MINERALS, AND EXERCISE 95


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