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Interest in performance-enhancing supplements is growing among younger athletes despite serious unresolved questions about safety and efficacy. Here&s the information you need to talk to your patients about supplements.
|Jump to:||Choose article section... Booming market Creatine: No magic bullet DHEA and "andro": Risky business Amino acids: Try food Minerals: Selective benefits Carbohydrates: Cheap sources are plentiful Question your patients wisely|
Interest in performance-enhancing supplements is growing among younger athletes despite serious unresolved questions about safety and efficacy. Here's the information you need to talk to your patients about supplements they may be taking.
From the time of the early Olympic games, athletes have looked for something to enhance their performance and give them an advantage over the competition. In recent years, ergogenic supplements such as creatine, androstenedione, and amino acids have attracted growing interest. They are likely popular not only because they are touted as "natural" but because many do not contain banned substances, a concern for athletes at higher levels of competition.
Interest in performance enhancement has started to trickle down to younger athletes at lower levels of competition, purportedly as a result of increasing acceptance of the "win-at-all-cost" attitude at all levels of sport1 and because children are engaged in year-round, single-sport competition at younger ages. Pediatricians must be aware of issues affecting their athletic patients so that they can address them during office visits. One of those issues is nutritional supplementation.
If pediatricians are to provide effective education, they must know whether the young athletes in their practice are taking nutritional supplements and, if so, which ones. To that end, this article discusses popular supplements and considers their ergogenic potential, potential side effects, and usefulness in treating deficiency states and meeting increased nutritional requirements arising from athletics.
The supplement market has experienced major growth over the last several years. Since enactment of the Dietary Supplement Health Education Act of 1994, it has been largely unregulated as well, leading to increased availability of nutritional ergogenic aids. Any substance classified as a nutritional or dietary supplement is not subject to regulation by the Food and Drug Administration. There are no standards for purity, quality, or quantity of active compounds, and a substance cannot be removed from the market until it is proven to be unsafe. Manufacturers of supplements do not need to publish benefits or precautions. Supplements may be recommended to a young person by a coach or teammate to treat a suspected deficiency (for example, iron for tiredness), to meet an increased requirement of a certain substance related to athletics (more protein to build muscle), or solely to enhance performance.
Supplement use by athletes of all ages has been reported to be anywhere from 30% to 100%.2 Vitamin supplementation in British children 4 to 12 years of age is known to increase with socioeconomic status (that is, those with the least need are the most likely to receive supplements).3 It is unknown whether this finding pertains to performance-enhancing supplements or applies to children in the United States. None of the performance-enhancing supplements discussed in this article have been studied in youths under 18 years of age.1
Because the risks of supplements are unknown, prepubertal and pubertal children should be strongly discouraged from using them. They should be taught that there are more important issues related to athletic performance: namely, nutrition, genetics, and training. An ergogenic aid cannot compensate for inadequate training or a lack of talent, although some supplements can help compensate for nutritional deficiency.
A nitrogenous compound, creatine is synthesized in the liver, kidneys, and pancreas at a rate of 1 to 2 g/d from the body's stores of glycine, arginine, and methionine. Creatine is also found in foods, particularly meat and fish. It is present in skeletal muscle (95%), heart, brain, testes, and retina. In skeletal muscle, it helps generate adenosine triphosphate (ATP) for muscle contraction lasting less than 30 seconds.
Supplemental creatine increases production of phosphocreatine (PCr), which is involved in ATP synthesis, and thus may enhance production of ATP, allowing faster recovery after short bouts of maximal exercise and increasing the buffering capacity of muscles.4 Increasing the pool of PCr, along with delayed depletion and increased resynthesis, likely increases the intensity of a training session, meaning that the athlete can work harder, longer.
Average dry muscle creatine content varies, probably related to dietary habits and genetics. There appears to be a threshold, or maximum amount of creatine, that muscles can accommodate, which affects an athlete's response to creatine supplementation. Other factors that affect creatine supplementation are exercise, carbohydrates, and caffeine. Exercise and carbohydrate ingestion appear to enhance uptake of creatine4; caffeine has an unfavorable effect.5
One of the effects of creatine supplementation is fluid accumulation. Initially, creatine uptake causes water retention in muscle cells. This accounts for early gains in fat-free mass. Kraemer and Volek have proposed that increased hydration of muscle cells stimulates increased protein synthesis, but no published evidence exists to support this theory.6
The earliest studies of creatine that incorporated a "loading dose" of 20 to 30 g/d, taken in four divided doses for five days, showed this regimen to be an effective way to build up creatine stores. Researchers have subsequently found that the same increase can be achieved by taking 2 to 3 g/d over the course of a month.7 Creatine stores can be maintained with a daily dosage of 2 to 3 g (or 0.3 g/kg).
Creatine supplementation has been studied in athletes for its ergogenic potential since the early 1990s. It became widely available about 1993. Research supports creatine's ergogenic effect in activities that require power and strength and some activities that involve repeated bouts of exercise. Harris and colleagues, in a placebo-controlled, single-blind study, demonstrated an overall decrease in running time for four 1,000-meter runs as well as a decrease in the time for the final 1,000 meters.8
A study of both single-sprint efforts and repetitive sprints found that supplementation is of benefit in repetitive efforts only.9 An increase in total lifting volume for weight-trained athletes after 28 days of supplementation has been reported.10 This effect also has been demonstrated in previously untrained women after taking creatine for 10 weeks.11 An increase in repetitions and power in bench press and jump squat was found to occur with short-term creatine use and, subsequently, with longer term (12 weeks') supplementation.12,13 A study of college football players reported strength gains in bench press, squat, and power clean maneuvers, as well as faster cycling sprints.14 All of these studies were placebo controlled and double blinded.
Two other studies demonstrated that creatine has a positive effect on performance of maximal cycling bouts by active persons.15,16
Creatine supplementation does not seem to be of benefit in endurance sports or even in improving one-time, all-out performance. In running or cycling sprints, creatine helps the athlete to maintain a higher level of intensity in training and possibly to complete later repetitions in a set more quickly than without supplementation.
The most common side effects, which are dose related, include weight gain, headache, abdominal pain, and diarrhea.17 Users of creatine appear to suffer more muscle strains than other athletes.17 They are probably at increased risk of dehydration or heat illness due to fluid shifts early in use.17 Some athletes discontinue taking creatine because of persistent side effects.
The theoretical risk of nephrotoxicity resulting from increased solute load is the most worrisome side effect. Poortmans investigated creatine and markers of renal function in 13 men and one woman without finding evidence of significant changes.18,19 A case of acute renal failure after creatine supplementation in a man with underlying renal disease was reported in 1998, however.20 Athletes with one kidney or any compromise in renal function should not use creatine, nor should any athlete with a family history of renal disease, until more is known about the risk of nephrotoxicity.21
Because the long-term effects of creatine supplementation are unknown, it should not be encouraged in any athlete. If a patient is already taking creatine or plans to take it, however, the best course is to provide education about the supplement rather than condemn its use. When asking a patient about creatine use, it is helpful to start with questions about whether his or her friends use it. Follow-up questions should then elicit interest in or past use of creatine or other performance enhancers. Once creatine use is established, find out how much the athlete is using and what the goals of supplementation are. A wrestler, for example, may be taking creatine in an attempt to get stronger. This is an opportune time to educate the patient about some of the effects of creatine, namely its propensity to increase weight.
Athletes should consider creatine supplementation as a training aid and understand that it will not greatly enhance performance without hard work. A loading dose is probably unnecessary and should be discouraged to minimize the risk of side effects and reduce the cost of supplementation to the athlete. Because long-term effects are not known, caution youngsters who use creatine not to exceed the dosages discussed above. More is not better.
Dehydroepiandrosterone (DHEA) and androstenedione ("andro") seem to be increasing in popularity. According to some workers in nutritional supplement chain stores, they are the supplements most requested by young people.22
DHEA is a hormone produced in the adrenal gland. It is a precursor of both androgens (androstenedione, testosterone, and dihydrotestosterone) and estrogens. Natural levels of DHEA decrease with age. Its exact mode of action is not known, but it is presumed to be at least mildly anabolic.23,24
DHEA and androstenedione supplements have not been studied in athletes, but because they are testosterone precursors, they may have some ergogenic effect. Increased serum levels of testosterone and estradiol in young men have been demonstrated after supplementation with androstenedione (300 mg/d for seven days).25 Although the study reported no adverse effects, the hormones could increase muscle mass and lead to hirsutism and clitoromegaly in females, gynecomastia in males, and precocious puberty or premature epiphyseal closure in physically immature athletes.25 Ingesting DHEA or androstenedione will likely cause an athlete undergoing drug testing to test positive. For all these reasons, athletes should avoid using DHEA and androstenedione.
Protein and amino acid supplements are very popular, especially with athletes involved in strength training. Athletic training has been shown to increase the daily requirement for protein; endurance athletes require 1.2 to 1.4 g/kg/d, and resistance-trained athletes need a slightly higher amount, 1.4 to 1.8 g/kg/d (the recommended daily allowance [RDA] is 0.8 g/kg/d).26 These requirements usually can be met by increasing caloric intake rather than by taking amino acid supplements.
The popular thinking is that supplements increase muscle mass because amino acids are building blocks of muscle. A study comparing a carbohydrate supplement to a weight-gain powder containing numerous amino acids, vitamins, and minerals in two groups of athletes undergoing resistance training found no significant difference between the groups, which both increased lean muscle mass.27 This finding supports the supposition that calories and muscle stimulation, not necessarily amino acids, are needed to promote lean muscle mass. The scientific literature contains little information on side effects associated with amino acid supplementation. Although supplementation cannot be recommended for young athletes, certain amino acids may have more benefits than others and warrant further investigation.
Glutamine. The amino acid glutamine is known to decrease after exertion, but a deficiency state has not been described. Glutamine has been shown to have some action on lymphocytes, leading to the theory that it could help prevent the decreased immune function that accompanies overtraining.27 Glutamine also may increase protein synthesis, but it is not clear if it is anabolic in athletes.27 Further investigation of the ergogenic effects of glutamine in athletes is warranted.
Branched chain amino acids. An athlete whose diet is lacking in the essential branched chain amino acids (BCAA), leucine, isoleucine, and valine, could develop a deficiency state. With anaerobic and resistance exercise, the plasma level of most amino acids decreases; with aerobic exercise, the plasma level decreases only when glycogen stores are reduced.28
Enzymes responsible for the metabolism of BCAAs are found primarily in skeletal muscle, leading to the assumption that they can be used directly as an energy source for exercising muscles.29 Supplementation with branched chain amino acidsleucine in particularincreases levels of these amino acids and may decrease the amount of catabolism that occurs with exercise.28 Leucine also may stimulate protein synthesis.28 A study of BCAA supplementation in wrestlers on calorie-restricted diets found an insignificant increase in fatty acid oxidation byproducts and a slight selective decrease in abdominal adipose tissue.30 Supplementation of leucine has not translated into improved performance or increased muscle mass, but this is an area of future research potential.
ß-hydroxy-methylbutyrate (HMB) is a product of the metabolism of leucine. Like leucine, HMB may inhibit muscle catabolism during strenuous exercise, as evidenced by reduced levels of enzyme markers of muscular damage.31 Researchers also found an increase in lean tissue and strength when 3 g of HMB a day is coupled with resistance training.31 No adverse effects were reported with short-term use of this supplement.
Carnitine is a naturally occurring substance that is synthesized from the amino acids lysine and methionine. It is present in meat and dairy products and is also available as a commercial supplement. Most of the body's stores are in skeletal and cardiac muscle.
Carnitine transports long-chain fatty acids through the mitochondria, thus facilitating their use as an energy source. Although fatty acid oxidation is the major energy source in prolonged, low-intensity, or endurance exercise, carnitine supplementation has not been found to have any effect on metabolism or performance in trained marathon runners.32 There is little evidence that carnitine has an ergogenic effect or that athletes develop a deficiency state.33
Mineral supplements most commonly taken by athletes include chromium, iron, and calcium. All are available from dietary sources, and only iron and calcium may require supplementation to treat deficiency.
Chromium helps regulate carbohydrate, lipid, and protein metabolism by enhancing the action of insulin.34 It is released from body stores in response to a rise in blood insulin and improves glucose tolerance in people with impaired tolerance.34 It is found in brewer's yeast, nuts, asparagus, prunes, mushrooms, wine, and beer.
The form of chromium most commonly used in supplements is chromium picolinate. It is more popular with adults than adolescents but may be taken by anyone desiring a change in weight. It is an ingredient in many over-the-counter diet pills. Athletes may have a slightly increased requirement for this mineral because of losses through sweat and urine, but a deficiency state is rare.34
Research into the ability of chromium to selectively decrease body fat and increase lean body mass and muscle strength has failed to demonstrate any such effects.35,36 Studies have found no significant difference between control groups and groups receiving supplemental chromium, both of which increased lean body mass with resistance training.37,38 Patients should be cautioned about taking chromium, especially in light of a case report of acute renal failure after six weeks of supplementation with 600 µg/d.39
Iron. The role of iron in hemoglobin production and oxygen carrying capacity is well described. Athletes are known to have increased loss of iron through sweat, feces, and urine (as both hemoglobinuria and myoglobinuria); girls also have ongoing menstrual loss of iron. The RDA for iron is 15 to 18 mg for females 11 to 24 years of age, 12 mg for males 11 to 18 years of age, and 10 mg for males 19 to 24 years of age. Endurance athletes seem to have an especially increased iron requirement, which depends on individual rates of absorption and the intensity, frequency, and duration of training.40
An exhaustive discussion of anemia in athletes is beyond the scope of this article, but suffice it to say that, in monitoring this population, you should be aware of the dilutional pseudoanemia ("sports anemia") that results from the physiologic increase in plasma volume with training.
Iron supplementation is indicated to treat true iron deficiency anemia. It is also beneficial in treating the athlete with low iron stores, as evidenced by a low ferritin level (less than 20 µg/L).41 Although ferritin usually correlates well with iron stores, it is an acute phase reactant and therefore can be falsely normal or elevated in an acutely ill person. One study found the ferritin level to correlate with maximum aerobic capacity,41 and iron supplementation is therefore often employed to try to increase maximum oxygen uptake (VO2max).40 Most experts believe that this approach is of questionable benefit.
It is usually best for the athlete to increase dietary sources of iron to remedy a deficiency (see the patient handout, "Foods that contain iron," on the right) and use supplemental iron only if clearly indicatednot simply for its ergogenic effect. The most common side effect of iron supplementation is constipation or gastric discomfort. Risks of long-term iron supplementation are unknown.
Calcium. Calcium-deficient persons are at increased risk of osteoporosis.2 This tends to be more of a problem for girls than boys. Girls, especially those who participate in endurance and "appearance" sports (such as gymnastics, figure skating, and equestrian events), have a lower caloric intake than other youngsters and often do not meet the recommended daily consumption of calcium, which is 1,200 to 1,500 mg for 11- to 24-year-olds.
Girls who are in a low estrogen state, as many very active girls are, need an even higher calcium intake to maintain the calcium balance.42 A history of oligomenorrhea or amenorrhea suggests that the patient has a lower-than-normal estrogen level and, therefore, a higher calcium requirement. Other factors that raise the daily calcium requirement are cigarette smoking, alcohol consumption, excessive caffeine ingestion (more than two cups of coffee a day), and a high-phosphorus diet (large amounts of meat or soda). A negative calcium balance, combined with excessive repetitive bone stress from weight bearing activity, increases the risk of stress fracture (when osteolysis exceeds osteoblast activity).
Recommendations include estrogen supplementation for amenorrheic or oligomenorrheic females, maximizing calcium in the diet (see the patient handout, "Foods that contain calcium," below), and calcium supplementation. An oral contraceptive is a convenient way to supply estrogen. Calcium carbonate antacid tablets can provide inexpensive calcium supplementation. Raloxifene, a treatment for osteoporosis, is contraindicated in girls and women of child-bearing age because it may cause harm to the fetus.
Carbohydrate ingestion in the form of sports drinks and athletic snack bars continues to grow in popularity. Many athletes engage in "carbo loading," consuming a meal consisting mainly of carbohydrates on the day, or several days, before competition to optimize muscle glycogen stores.42 For the same reason, it is important to replace carbohydrates that have been lost through exercise. Replacing losses in one or two hours promotes maximum muscle uptake.42 This can be done in whatever manner is most palatable and convenientpasta, a sports bar, or beverage, for example. Sports drinks and bars are convenient, but other sourcessuch as pasta, cereals, breads, fruits, vegetables, cookies, and yogurtprovide the same amount of carbohydrate more economically.
Rankin reports that a carbohydrate-protein mix consumed after exercise allows for muscle glycogen repletion and may decrease muscle-protein breakdown and increase protein synthesis.29 This theory warrants further study.
Consumption of nutritional supplements by athletes of all ages is prevalent. Those who provide health care to young people should question patients about their use of supplements to guide them appropriately. When counseling young athletes, keep in mind that all the research has been performed on adults, not children, and that the effects of long-term supplement use and use during periods of rapid growth are unknown.
At a time when we are encouraged to see patients as expeditiously as possible, a lengthy discussion of ergogenic supplements is not often possible at a visit for a sports physical. It is important to determine what your patient is using, and why, so that you can open a dialogue that can continue in later visits.
The author thanks Greg Landry, MD, for his review of the manuscript of this article.
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2. Armstrong LE, Maresh CM: Vitamin and mineral supplements as nutritional aids to exercise performance and health. Nutr Rev 1996;54(SII):S149
3. Bristow A, Qureshi S, Rona RJ, et al: The use of nutritional supplements by 4-12-year-olds in England and Scotland. Eur J Clin Nutr 1997;51 (6):366
4. Demant TW: Effects of creatine supplementation on exercise performance. Sports Med 1999;28(1):49
5. Vandenberghe K, Gillis N, VanLeemputte M, et al: Caffeine counteracts the ergogenic action of muscle creatine loading. J Appl Physiol 1996;80(2):452
6. Kraemer WJ, Volek JS: Creatine supplementation: Its role in human performance. Clin Sports Med 1999; 18(3):651,ix
7. Hultman E, Soderlund K, Timmons JA, et al: Muscle creatine loading in men. J Appl Physiol 1996;81(1):232
8. Harris RC, Viru M, Greenhaff PL, et al: The effect of oral creatine supplementation on running performance during maximal short-term exercise in man. J Physiol 1993; 467:74 P
9. Peyrebrune MC, Nevill ME, Donaldson FJ, et al: The effects of oral creatine supplementation on performance in single and repeated sprint swimming. J Sports Sci 1998;16(3):271
10. Earnest CP, Snell PG, Rodriguez R, et al: The effect of creatine monohydrate ingestion on anaerobic power indices, muscle strength, and body composition. Acta Physiol Scand 1995;153:207
11. Vandenberghe K, Goris M, Van Hecke P, et al: Long-term creatine intake is beneficial to muscle performance during resistance training. J Appl Physiol 1997; 83(6):2055
12. Volek JS, Kraemer WJ, Bush JA, et al: Creatine supplementation enhances muscular performance during high-intensity resistance exercise. J Am Diet Assoc 1997;97:765
13. Volek JS, Duncan ND, Mazzetti SA, et al: Performance and muscle fiber adaptations to creatine supplementation and heavy resistance training. Med Sci Sports Exerc 1999;31(8):1147
14. Kreider RB, Ferreira M, Wison M, et al: Effects of creatine supplementation on body composition, strength, and sprint performance. Med Sci Sports Exerc 1998;30(1):73
15. Casey A, Constantin-Teodosiu D, Howell S, et al: Creatine ingestion favorably affects performance and muscle metabolism during maximal exercise in humans. Am J Physiol 1996;271:31
16. Smith JC, Stephens DP, Hall EL, et al: Effect of oral creatine ingestion on parameters of the work rate-time relationship and time to exhaustion in high intensity cycling. Eur J Appl Physiol 1998;77(4):360
17. Juhn MS, Tarnopolsky M: Potential side effects of oral creatine supplementation: A critical review. Clin J Sport Med 1998;17(4):298
18. Poortmans JR, Auquier H, Renaut V, et al: Effect of short-term creatine supplementation on renal responses in men. Eur J Appl Physiol 1997;76:566
19. Poortsman JR: Long-term oral creatine supplementation does not impair renal function in healthy athletes. Med Sci Sports Excer 1999;31(8):1108
20. Pritchard NR, Kalra PA: Renal dysfunction accompanying oral creatine supplements. Lancet 1998;351(9111):1252
21. Greenhaff PL: Renal dysfunction accompanying oral creatine supplements (correspondence). Lancet 1998; 18.352 (9123):233
22. Personal communication, 2000
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The recommended daily intake of iron is 15 to 18 milligrams (mg) for girls and women 11 to 24 years of age, 12 mg for boys 11 to 18 years of age, and 10 mg for young men 19 to 24 years of age. The best way to get iron is from foods such as those listed below (along with the amount of iron they contain). If you have anemia, you may need more iron, and your doctor may prescribe a supplement. Do not take an iron supplement unless your doctor advises you to do so.
|Liver, 4 oz cooked||9 mg|
|Beef, 4 oz||3 mg|
|Turkey, 4 oz dark meat||2 mg|
|Pork, 4 oz||1 mg|
|Shrimp, 12 large||2 mg|
|Chicken breast, 4 oz||1 mg|
|Fish/tuna, 4 oz||1 mg|
|Egg, 1 large||1 mg|
|Prune juice, 8 oz||3 mg|
|Apricots, 5 halves dried||0.8 mg|
|Dates, 10 dried||1 mg|
|Raisins, 1/3 cup||1 mg|
|Refried beans, 1 cup||4.5 mg|
|Spinach, 2 cups cooked||3 mg|
|Peas, 2 cups||1 mg|
|Broccoli, 2 cups||1 mg|
|Milk, 1 cup skim||0.1 mg|
|Cheddar cheese, 1 oz||0.2 mg|
|Total cereal, 1 cup||18 mg|
|Raisin Bran,||18 mg|
|Cream of Wheat, 1 cup||9 mg|
|Cheerios, 1 cup||4.5 mg*|
|Quaker flavored instant oatmeal 1 serving||2 mg|
|Pasta, 1 cup cooked, enriched||1 mg|
|Bread, 1 slice enriched||1 mg|
|Brown rice, 1 cup cooked||1 mg|
|Brewers yeast, 1 oz (homemade bread)||5 mg|
|Molasses, 1 tablespoon blackstrap (found in some dark breads and can be used to sweeten oatmeal)||3.5 mg|
|Wheat germ,||2 mg|
Factors that can interfere with your bodys ability to absorb calcium and use it to build strong bones include:
|Whole, 8 oz||291 mg|
|Skim, 8 oz||302 mg|
|Low fat plain, 8 oz||415 mg|
|Low fat with fruit, 8 oz||343 mg|
|Frozen (fruit), 8 oz||240 mg|
|Ice cream, soft serve, 1 cup||274 mg|
|McDonalds vanilla, 15 oz||320 mg|
|Burger King, 10 oz||240 mg|
|Muenster, 1 oz||203 mg|
|Cheddar, 1 oz||204 mg|
|Ricotta, part skim, 1 cup||167 mg|
|Mozzarella, part skim, 1 oz||207 mg|
|Fortified orange juice, 8 oz||300 mg|
|Salmon, 3 oz||167 mg|
|Shrimp, 3 oz||100 mg|
|Collards, cooked from raw, 1 cup||252 mg|
|Broccoli, cooked, 1 cup||100136 mg|
|Spinach, cooked,||122 mg|
|Tofu in oriental foods (stir fry and soups), 4 oz||150250 mg|
Wendi Johnson. Nutritional supplements and the young athlete: What you need to know.