09 Shorter (481)

International Journal of Sport Nutrition and Exercise Metabolism, 2004, 14, 481-492 © 2004 Human Kinetics Publishers, Inc.

Prevalent Use of Dietary Supplements Among People Who Exercise At a Commercial Gym Laura J. Morrison, Frances Gizis, and Barbara Shorter Supplement use was surveyed in a convenience sample of persons who exercised regularly at a Long Island, NY gym. Participants, age at least 18 y, completed anonymous questionnaires. A majority (84.7%) took supplements. Many consumed multivitamin/minerals (MVM; 45%), protein shakes/bars (PRO; 42.3%), vitamin C (34.7%), and vitamin E (VE; 23.4%) at least 5 times per wk. Other dietary supplements were used less frequently or by fewer participants. Ephedra was consumed by 28% at least once per wk. Choices and reasons for dietary supplement use varied with age of the participant. More of the oldest consumed MVM or VE, while those 45 y or younger chose PRO. Those younger than 30 consumed creatine more frequently. The oldest participants took supplements to prevent future illness, while others took supplements to build muscle. The reason for committing to an exercise program influenced supplement use. Bodybuilders more frequently consumed PRO, creatine, and ephedra compared to those exercising for health reasons. Key Words: athletic training, ephedra, ergogenic aids, nutrient supplementation

Since the passage of the Dietary Supplement Health and Education Act (DSHEA) in 1994, a wide variety of compounds have become readily available in the United States. A dietary supplement, according to DSHEA, includes one or more of the following ingredients: vitamin, mineral, herb or other botanical, amino acid, concentrate, metabolite, constituent, and/or extract. Examples of these compounds include creatine, ephedra, chromium picolinate, protein or carbohydrate bars/shakes, and glutamine. Studies have measured the extensive use of vitamin and mineral supplements by Americans (1–3, 5–7, 12, 15, 17, 18, 25–27). Few studies have examined the use of the other products included in DSHEA (15, 20), and little information is available regarding supplement use among selected groups. Survey results have shown that dietary supplements have been taken to improve performance, increase strength, gain muscle mass, lose weight, prevent illness and disease, treat medical problems, boost immunity, compensate for inadequate diet, provide extra energy, meet special nutrient demands for high levels of physical activity, improve fitness, increase alertness or mental activity, reduce stress, and feel better (16, 17, 22, 24). The authors are with the Nutrition Department at the C.W. Post Campus of Long Island University, Brookville, NY 11548. 481

Morrison, Gizis, and Shorter

482

While some supplements may be beneficial, others have been shown to have no effect or to be dangerous. Many adverse effects from the use of various supplements have been reported to the FDA (4). People who frequent commercial gyms may use particular supplements for a variety of reasons. Differences may exist in the choice of supplement depending on age, gender, or reason for exercise. It is important to determine what supplements people who exercise take, why they take them, and their sources of information in order to help health professionals educate this population. Some people may learn about supplements from unqualified sources rather than health professionals. Eliason et al. (6) found that participants who purchased supplements at a health store did not rely on physicians or other health professionals for supplement information. This study examined the use of supplements by people who exercise and determined the source from which these people obtained information.

Methods and Materials Selection of Population To be included in this study, subjects attending a commercial gym in a suburb of Long Island, NY exercised at least 4 times per wk at 1 h per session, and had been exercising at this intensity for at least 1 y. A preliminary questionnaire was administered, regarding the above criteria. A convenience sample of 222 people, 18 y and older, met qualification standards and completed the survey. Questionnaire The survey included questions concerning demographic characteristics such as age, gender, education, employment, and health status. Data concerning type and frequency of supplement use, reasons for supplement use, main reason for exercising, and sources of supplement information were collected. The anonymous survey, consisting of 25 questions, was developed based on previously published studies (5–7,17, 21, 25, 26). It was reviewed and evaluated by faculty, colleagues, and registered dietitians for readability and content validity. A similar population at 2 different gyms on Long Island, New York pilot tested the questionnaire. Data Collection Surveys were distributed and collected on the same day by the researcher. Following completion of the questionnaire, each participant was given an energy bar and asked if they had forgotten to list any supplements. If so, they were given the opportunity to make the appropriate revisions. Data were collected over a period of 2 d by 1 researcher (LM). Data Analysis Analyses of data were performed using SPSS for Windows (v. 10.0, SPSS Inc., Chicago, IL). Descriptive statistics including frequency distribution were developed. When data were incomplete, a reduced n was used. Comparisons were made by chi square. Differences were considered significant if the P value was < 0.05. Group-by-group comparisons were considered significant at P < 0.017 (Bonferroni correction).

Supplement Use at a Commercial Gym

483

Results Demographics Participants of the study were primarily male (82.0%) and Caucasian (80.4%). A majority of the subjects (86.4%) attended or had graduated from college, and 19.0% had started or completed advanced degrees. Almost half (46.5%) of the subjects reported working in business, while 21.7% had other, unspecified occupations. Participants considered themselves to be healthy; excellent health was reported by 50.7% and good health by 43.9%. The population tended to be young; 52.3% were 30 y or younger (Table 1A). For comparative purposes, 3 age groups were established: Group 1, participants who were 18 to 30 y (n = 113); Group 2, 31 to 45 y (n = 68); and Group 3, 46 y and older (n = 35). Data were not analyzed separately for females because of the small numbers in the survey (n = 40). The types of exercise reported in Table 1B included weightlifting by 86.4% of participants, endurance/cardiovascular exercise by 73.6%, and strength training by 53.6 %. Few (16.8%) reported engaging in circuit training.

Table 1A Age of Subjects Exercising at a Commercial Gym Age of subjects 18–20 21–25 26–30 31–35 36–40 41–45 46–50 51–55 56–60 > 60

N

%

14 59 40 32 21 15 15 13 5 2

6.5 27.3 18.5 14.8 9.7 6.9 6.9 6.0 2.3 0.9

Note. Missing data n = 6; 2.7%.

Table 1B Types of Exercise at a Commercial Gym Type of exercise Weightlifting Endurance/cardiovascular Strength training Circuit training

N

%

190 162 118 37

86.4 73.6 53.6 16.8

Note. More than 1 response possible. Missing data n = 2; 0.9%.


484

Table 1C

Main Reason for Exercising at a Commercial Gym Reason

N

%

Bodybuilding Health reasons Endurance/cardiovascular Weight loss Improve performance in a sport

65 43 19 18 16

29.7 19.6 8.7 8.2 7.3

Note. Missing data n = 61; 27.5%.

Supplement Use A majority (84.7%) of the subjects reported taking at least 1 supplement, and 93.4% of these persons had been taking them for at least 1 y. Of those using these products, 94.5% consumed supplements throughout the year, and only 5.5% took them during specific seasons. Participants were asked to reveal the types and frequency of use of all the supplements they were consuming at the time of the study (Table 2). The four that were taken “regularly” (more than 5 times per wk) by the largest proportion of the participants included: multivitamin and minerals (MVM; 45.0%), protein shakes/bars (PRO; 42.3%), vitamin C (34.7%), and vitamin E (23.4%). Also used on a regular basis were calcium (17.1%), B complex vitamins (16.2%), carbohydrate shakes/bars (14.4%), glutamine (14.0%), ephedra/Ma Huang (13.1%), and creatine (12.6%). When comparing supplement use by age group (Table 3), more of those in Group 3 (46 y and older) consumed multivitamin and mineral supplements compared to participants in Group1 (ages 18 to 30 y; P = 0.006). A higher percentage of those in Group 3 regularly consumed vitamin E compared to those in either Group 2 (P = 0.0003) or Group 1 (P = 0.0001) Supplement use was also categorized as taken or not taken. Taken included the categories regularly, occasionally, and seldom. Protein shakes/bars were taken by 54.9% of participants, creatine (33.3%), carbohydrate shakes/bars (30.2%), ephedra/Ma Huang (27.9%), glutamine (27.1%), chromium picolinate (18.9%), carnitine (16.7%), ginseng (16.2%), arginine (14.9%), ornithine (13.5%), and androstenedione (13.1%). When data were compared by age group as taken or not taken (Table 4), the use of 3 supplements varied significantly by age group. An increased use of vitamin E by the oldest participants in Group 3 was identified, compared to the younger participants in Group 1 (P = 0.017). In addition, more in the 2 younger Groups 1 (P = 0.004) and 2 (P = 0.005) selected protein shakes/bars compared to the oldest participants of Group 3. More of the youngest subjects of Group 1 chose creatine compared to the oldest participants of Group 3 (P = 0.001). Reasons for Supplement Use Participants who could list as many reasons as desired indicated that supplements were chosen to build muscle (49.1%), prevent future illness (38.4%), increase energy


Table 2

485

Supplements Used By Subjects Who Exercise at a Commercial Gym Regularly

Supplement Multivitamin/mineral Multivitamin/no mineral B-complex Vitamin C Vitamin E Other antioxidants Iron Calcium Chromium picolinate Carbohydrate shakes/bars Protein shakes/bars Glutamine Carnitine Arginine Ornithine Creatine Other amino acids Androstenedione Yohimbe Ginseng Ephedra/Ma Huang Dehydroepiandrosterone (DHEA) Other herbs Other

Occasionally

Seldom

Never

n

%

n

%

n

%

n

%

100 19 36 77 52 14 23 38 18 32 94 31 15 8 9 28 4 4 4 8 29

45.0 8.6 16.2 34.7 23.4 6.3 10.4 17.1 8.1 14.4 42.3 14.0 6.8 3.6 4.1 12.6 1.8 1.8 1.8 3.6 13.1

26 16 14 24 18 2 9 10 11 19 20 14 8 10 6 24 2 3 9 12 18

11.7 7.2 6.3 10.8 8.1 0.9 4.1 4.5 5.0 8.6 9.0 6.3 3.6 4.5 2.7 10.8 0.9 1.4 4.1 5.4 8.1

15 13 12 11 14 7 20 15 13 16 8 15 14 15 15 22 6 22 11 16 15

6.8 5.9 5.4 5.0 6.3 3.2 9.0 6.8 5.9 7.2 3.6 6.8 6.3 6.8 6.8 9.9 2.7 9.9 5.0 7.2 6.8

81 174 160 110 138 197 170 159 180 155 100 162 185 189 192 148 210 193 198 186 160

36.5 78.4 72.1 49.5 62.2 89.1 76.6 71.6 81.1 69.8 45.0 73.0 83.3 85.1 86.5 66.7 94.6 86.9 89.2 83.8 72.1

6 6 13

2.7 2.7 6.0

4 0 2

1.8 0.0 0.9

11 2 0

5.0 0.9 0.0

201 210 202

90.5 94.6 91.0

Note. Regularly = greater than 5 times per wk; occasionally = 2 to 4 times per week; seldom = 1 to 2 times per wk or less; never = not taken.

(36.1%), improve performance in a sport (24.4%), gain strength (22.4%), and aid in recuperation (20.5%). Other reasons for taking supplements were reported less frequently. Three reasons for taking supplements varied significantly by age group (Table 5). More in Groups 1 (P = 0.0002) and 2 (P = 0.0001) took supplements to build muscle compared to the older participants of Group 3. More of the oldest participants in Group 3 consumed supplements to prevent future illness or disease compared to the youngest participants in Group 1 (P = 0.009). There was some trend that more of the youngest participants (Group 1) chose supplements to gain strength compared to Group 2 (P = 0.028) and Group 3 (P = 0.027). Although the overall comparison of the 3 groups indicated a significant difference by age group, group-by-group comparisons were not significant at the P < 0.017 level. Participants (15.3%, n = 34) who reported not taking supplements believed that they do not work (38.2%) and that enough nutrients were obtained from their diet (35.3%).


486

Table 3 Comparison By Age for Supplements Taken Regularly Versus Occasionally, Seldom, or Never Group 1 (age 18 to 30; n = 113) Supplementa Multivitamin and mineralc Regularly Sometimes, occasionally, never Vitamin Ed Regularly Sometimes, occasionally, never

Group 2 (age 31 to 45; n = 68)

Group 3 (age 46+; n = 35)

n

%

n

%

n

%

40

35.4

36

52.9

21

60.0

73

64.6

32

47.1

14

40.0

18

15.9

13

19.1

19

54.3

95

84.1

55

80.9

16

45.7

Pb

.010

.0001

Note. Regularly = greater than 5 times per wk, occasionally = 2 to 4 times per wk, seldom = 1 to 2 times per wk. aComparisons for all other supplements not significantly different; bchi square. cGroup 1 significantly different from Group 3 (P = 0.006); dGroup 3 significantly different from Group 1 (P = 0.0001) and Group 2 (P = 0.0003).

Table 4

Supplements “Taken” Compared By Agea Group 1 (age 18 to 30; n = 113)

Group 2 (age 31 to 45; n = 68)

Group 3 (age 46+; n = 35)

Supplementa

n

%

n

%

n

%

Pb

Vitamin Ec Taken Not Taken

39 74

34.5 65.5

23 45

33.8 66.2

20 15

57.1 42.9

.038

Protein shakes/barsd Taken Not taken

67 46

59.3 40.7

41 27

60.3 39.7

11 24

31.4 68.6

.009

Creatinee Taken Not taken

47 66

41.6 58.4

22 46

32.4 67.6

4 31

11.4 88.6

.004

Note. “Taken” = the categories regularly, occasionally, and seldom. aComparisons for all other supplements are not significantly different; bchi square. cGroup 3 significantly different from Group 1 (P = 0.017); dGroup 3 significantly different from Group 1 (P = 0.004) and Group 2 (P = 0.005); eGroup 3 significantly different from Group 1 (P = 0.001).


Table 5

487

Reason for Taking Supplements Compared By Age Group 1 (age 18 to 30; n = 113)

Group 2 (age 31 to 45; n = 68)

Group 3 (age 46+; n = 35)

Reasona

n

%

n

%

n

%

Pb

To build musclec Take at least 1 supplement No supplement

63 49

56.3 43.8

37 30

55.2 44.8

6 29

17.1 82.9

.0001

To prevent future illnessd Take at least 1 supplement No supplement

35 77

31.3 68.8

29 39

42.6 57.4

19 15

55.9 44.1

.026

To gain strength Take at least 1 supplement No supplement

34 79

30.1 69.9

10 55

15.4 84.6

4 31

11.4 88.6

.018

e

Note. More than one response possible. aComparisons for all other reasons are not significantly different; bchi square. cGroup 3 significantly different from Group 2 (P = 0.0001) and Group 1 (P = 0.0002); dGroup 3 significantly different from Group 1 (P = 0.009); eGroup 1 compared to Group 2 (P = 0.028) and Group 3 (P = 0.027).

Main Reason for Exercise One item in the questionnaire asked subjects to indicate their main reason for exercise; however, 27.5% (n = 61) reported more than 1 reason so that data from these participants could not be further analyzed. The main reason for exercise reported by the 161 participants who correctly answered this question (Table 1C) was bodybuilding (29.7%) followed by health reasons (19.6%). Other responses were less frequently reported, and thus data were not further analyzed [endurance/cardiovascular (8.7%), weight loss (8.2%), improve performance in a sport (7.3%)]. As shown in Table 6, of those participants who exercised for bodybuilding (n = 65): 72.3% selected protein, 61.5% multiple vitamin and mineral supplements, 52.3% creatine, 49.2% ephedra, 49.2% vitamin C, 43.1% glutamine, and 36.9% carbohydrates. For those subjects who exercised for health reasons (n = 43), 60.5% chose multiple vitamin and mineral supplements, 44.2% protein, 41.9% vitamin C, 37.2% vitamin E, 27.9% calcium, and 25.6% creatine. Comparison of supplement use by those who exercised for bodybuilding or health reasons indicated that significantly more of those who took supplements for bodybuilding took protein shakes/bars (P = 0.003), creatine (P = 0.006), or ephedra (P = 0.0001). Sources of Information To learn about supplements, the following sources of information were used by more than half of the participants: magazines (65.8%), family/friends (63.1%),


488

Table 6

Main Reason for Exercise Versus Supplementation Bodybuilding (n = 65)

Supplement Multivitamin with minerals Multivitamin without minerals B-complex Vitamin C Vitamin E Other antioxidants Iron Calcium Chromium picolinate Carbohydrate shakes/bars Protein shakes/barsa Glutamine Carnitine Arginine Ornithine Creatinea Other amino acids Androstenedione Yohimbe Ginseng Ephedra/Ma Huanga Dehydroepiandrosterone (DHEA) Other herbs Other

Health reasons (n = 43)

n

%

n

%

40 15 17 32 19 5 16 16 13 24 47 28 14 12 10 34 6 9 10 12 32 7 1 3

61.5 23.1 26.2 49.2 29.2 7.7 24.6 24.6 20.0 36.9 72.3 43.1 21.5 18.5 15.4 52.3 9.2 13.8 15.4 18.5 49.2 10.8 1.5 4.8

26 7 11 18 16 8 9 12 9 12 19 8 7 6 6 11 4 8 4 9 7 4 3 5

60.5 16.3 25.6 41.9 37.2 18.6 20.9 27.9 20.9 27.9 44.2 18.6 16.3 14.0 14.0 25.6 9.3 18.6 9.3 20.9 16.3 9.3 7.3 11.9

Note. More than 1 response for supplementation possible per reason. aSignificantly different: protein shakes/bars (P = 0.003), creatine (P = 0.006), ephedra/Ma Huang (P = 0.0001).

personnel at a vitamin/health food store (55.7%), and books (54.5%). Many subjects (45.5%) relied on the media and 38.7% on personal trainers. A third or fewer of the participants indicated consulting a physician (33.8%), registered dietitian/certified dietitian/nutritionist (28.4%), pharmacist (17.1%), and/or chiropractor (16.4%) for supplement information. Approximately 49% of subjects who took supplements reported checking qualifications of those who supplied them with information.

Discussion Previous studies have shown that subjects tend to underreport their supplement use (7, 13). The current study followed the recommendations of Hensrud et al. (13). Written responses about supplement use were followed by a discussion to determine


489

if any additional supplements may have been taken. The participants were given the chance to make appropriate revisions as needed. In this study, a higher percentage of subjects reported taking supplements (84.7%) compared to reports of other populations (7, 15, 26, 27). Previous research and the results of the current study have shown that vitamins and minerals were the most frequently chosen supplements (5, 7, 15, 18, 29). Few studies have reported the use of supplements, such as protein or carbohydrate shakes/bars, glutamine, ephedra/Ma Huang, creatine, chromium picolinate, or other botanicals (15, 20). In this study, many participants (42.3%) consumed protein shakes/bars and from 8% to 14% reported selection of carbohydrate shakes/bars, glutamine, ephedra, creatine, or chromium picolinate on a regular basis (greater than 5 times per wk). The Commission on Dietary Supplement Labels indicated that ephedra was one of the top 10 botanical products sold in selected U.S. health food stores in 1995 (23). In the present study, ephedra was supplemented “regularly” by 13.1% and taken at least 1 to 2 times per wk by 27.9% of subjects. The use of ephedra has been of concern because it has been linked to several deaths and to more than 800 adverse effects since 1998 (4, 9, 11, 24). Kamber et al. (14) analyzed 75 products used for sports supplementation and found that some supplements contained caffeine and ephedrine when the compounds were “either not or not clearly declared on the labels.” Interestingly, the current study found that approximately 7 participants took supplements that contained ephedra as one of its ingredients, but the participants did not list ephedra as a supplement that they took. It is troubling that more supplements may have been taken by this population that contained ephedrine. It was only after the completion of the study that the researcher was made aware that some of the products listed in the questionnaire might have contained ephedra even though the company might not have indicated it. Few studies have compared supplement use by age group. In the present study, more older people tended to take multivitamin and mineral supplements and vitamin E regularly compared to younger people. More younger subjects in the present study consumed protein shakes/bars and creatine compared to older participants, although these supplements may not have been taken as frequently as 5 times per wk (regularly). Kaufman et al. (15) found that older persons took multivitamin and minerals supplements, while more younger men tended to take creatine. Consistent with previous studies, many persons took supplements to build muscle, prevent future illness, increase energy, improve performance in a sport, gain strength, or aid in recuperation (6, 17, 18, 23). The older people reported using supplements to prevent future disease or illness, while participants younger than 45 took at least 1 supplement to build muscle. Neuhouser et al. (18) showed that their subjects, who had a mean age of 44, took multivitamins to feel better, vitamin C to prevent acute illness, and vitamin E and calcium to avoid chronic disease. Because the number of older respondents in the current study is relatively small, further analysis with a larger representation of older persons is warranted. Comparisons were made for those subjects who reported that their main reason for exercise was bodybuilding (n = 65) and health reasons (n = 43). More of the bodybuilding group took the supplements creatine, protein shakes/bars, and ephedra that have been shown to aid or have been marketed for bodybuilding. Bodybuilders often use creatine to increase muscle creatine and phosphocreatine and enhance athletic performance (8, 10, 15). Ephedra, now banned, was


490

usually used for weight loss and was marketed for weight loss as well as enhanced athletic performance (24). The use of carbohydrate supplements by 36.9% of bodybuilders was unexpected, because many bodybuilders tend to follow a high protein, low carbohydrate diet. Many participants refused the energy bar that was offered to them after the completion of the questionnaire because it “contained too much carbs.” Carbohydrate supplementation has been shown to aid in prolonged, low- and moderate-intensity exercise (21). Neuhouser et al. (18) found that those people who reported that their main purpose for exercise was for health reasons used multivitamin and mineral supplements, vitamin C, vitamin E, and calcium as supplements to stay healthy and prevent future illness. Kaufman et al. (15) also found that supplements were used for nonspecific health reasons. Consistent with Eldridge and Sheehan’s study (5), many participants reported using the following sources of information regarding supplement use: magazines, family/friends, personnel at a vitamin/health food store, and books. One-third (34%) consulted physicians, which is consistent with previous studies (7, 18, 24, 28). Health professionals such as registered dietitians or certified dietitian/nutritionists and pharmacists were infrequently consulted. Eliason et al. (6) found similar results. In conclusion, many people who exercised extensively at a commercial gym took dietary supplements. A wide variety of vitamin and mineral supplements as well as other herbs and botanicals were chosen. At the time of this study 28% of the participants reported taking ephedra, and 7 additional subjects did not realize that they were doing so. Age of the respondent influenced the choice of supplement and the reason for taking supplements. Participants also chose different supplements, depending on their main reason for exercising. Health professionals were least frequently consulted for supplement information. Gyms, such as the one included in this study, may well need to have qualified health professionals such as nutritionists available to members. These professionals can provide accurate information about supplements and assist members to be aware of both positive as well as adverse health effects of dietary supplements.

References 1. Barron, R.L., and G.J. Vanscoy. Natural products and the athlete: facts and folklore. Ann. Pharmacother. 27: 607-615,1993. 2. Balluz, L.S., S.M. Kieszak, R.M. Philen, and J. Mulinare. Vitamin and mineral supplement use in United States: results from the third National Health and Nutrition Examination Survey. Arch. Fam. Med. 9:258-262, 2000. 3. Bazzarre, T.L., A. Scarpino, R. Sigmon, L.F. Marquart, S.L. Wu, and M. Izurieta. Vitaminmineral supplement use and nutritional status of athletes. J. Am. Coll. of Nutr. 12: 162-169,1993. 4. Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration. Dietary supplements: warnings and safety information. Retrieved 9/15/03 from http: //www.cfsan.fda.gov/~dms/ds-warn.html. 5. Eldridge, A.L., and E.T. Sheehan. Food supplement use and related beliefs: survey of community college students. J. Nutr. Educ. 26:259-265,1994. 6. Eliason, B.C., J. Kruger, D. Mark, and D.N. Rasmann. Dietary supplement users: demographics, product use, and medical system interaction. J. Am. Board Fam. Prac. 10:265-271, 1997.


491

7. Eliason, B.C., J. Myszkowski, A. Marbella, and D. Rasmann. Use of dietary supplement by patients in a family practice clinic. J. Am. Board Fam. Prac. 9:249-253,1996. 8. Feldman, E.B. Creatine: a dietary supplement and ergogenic aid. Nutr. Rev. 57:45-50, 1999. 9. Fetrow, C.W., and J.R. Avila. Professional’s Handbook of Complementary & Alternative Medicines. Springhouse, PA: Springhouse, 1999, pp. 239-242. 10. Francaux, M., R. Demeure, J.F. Goudemant, and J.R. Poortmans. Effect of exogenous creatine supplementation on muscle PCr metabolism. Int. J. Sports Med. 21:139-145, 2000. 11. Gurley, B.J., S.F. Gardner, L.M. White and P.L. Wang. Ephedrine pharmacokinetics after the ingestion of nutritional supplements containing ephedra sinica (Ma Huang). Therapeutic Drug Monitoring. 20:439-445,1998. 12. Grunewald, K.K., and R.S. Bailey .Commercially marketed supplements for bodybuilding athletes. Sports Medicine. 15:90-103, 1993. 13. Hensrud, D.D., D.D. Engle, and S.M. Scheitel .Underreporting of the use of dietary supplements and nonprescription medications among patients undergoing a periodic health examination. Mayo Clinic Proceedings. 74:443-447, 1999. 14. Kamber, M., N. Baume, M. Saugy, and L. Rivier. Nutritional supplements as a source for positive doping cases? Int. J. Sports Nutr. Exerc. Metab. 11:258-263, 2001. 15. Kaufman, D.W., J.P. Kelly, L. Rosenberg, T.E. Anderson, and A.A. Mitchell. Recent patterns of medication use in the ambulatory adult population of the United States: The Slone Survey. JAMA. 287:337-344, 2002. 16. Kraemer, W.J., and J.S. Volek. Nutritional aspects of exercise: creatine supplement—its role in human performance. Clinics in Sports Medicine. 18:651-666, 1999. 17. Krumbach, C.J., D.R. Ellis, and J.A. Driskel. A report of vitamin and mineral supplement use among university athletes in a Division I institution. Int. J. Sports. Nutr. 9: 416-425,1999. 18. Neuhouser, M.L., R.E. Patterson, and L. Levy. Motivations for using vitamin and mineral supplements. J. Am. Diet. Assoc. 99:851-854, 1999. 19. Philen, R.M., D.I. Ortiz, S.B. Auerbach, and H. Falk. Survey of advertising for nutritional supplements in health and bodybuilding magazines. JAMA. 268:1008-1011,1992. 20. Radimer, K.L., A.F. Subar, and F.E. Thompson. Nonvitamin, nonmineral dietary supplements: issues and findings from the third National Health and Nutrition Examination Survey. J. Amer. Diet. Assoc. 100:447-454, 2000. 21. Rauch, H.G.L., J.A. Hawley, M. Woodey, T.D. Noakes, and S.C. Dennis. Effects of ingesting a sports bar versus glucose polymer on substrate utilization and ultraendurance performance. Int. J. Sports Med. 20:252-257, 1999. 22. Read, M.A., R.L. Brunner, G. Miller, S.T. St. Jeor, B.J. Scott and T.P. Carmody. Relationship of vitamin/mineral supplementation to certain psychologic factors. J. Am. Diet. Assoc. 91:1429-1431, 1991. 23. Report of the Commission on Dietary Supplement Labels. (1997). Retrieved 9/15/03 from http://web.health.gov/dietsupp/ch2.htm. 24. Shekelle, P.G., M.L. Hardy, S.C. Morton, M. Maglione, W.A. Mojica, M.J. Suttorp, S.L. Rhodes, L. Jungvig, and J. Gagne. Efficacy and safety of ephedra and ephedrine for weight loss and athletic performance. JAMA. 289:1537-1545, 2003 25. Sobal, J., and L.F. Marquart. Vitamin/mineral supplement use among athletes: a review of the literature. Int. J. Sport Nutr. 4:320-334, 1994.

492


26. Sobal, J., and L.F. Marquart. Vitamin/mineral supplement use among high school athletes. Adolescence. 29:835-843, 1994. 27. Subar, A.F., and G. Block. Use of vitamin and mineral supplements: demographics and amounts of nutrients consumed. Am. J. Epidemiol. 132:1091-1101, 1990. 28. Stricker, P.R. Sports pharmacology: other ergogenic agents. Clinics in Sports Medicine. 17:283-297, 1998. 29. USDA Food Surveys Research Group. Supplementary data tables USDA’s 1994–1996 continuing survey of food intakes by individuals. 1999. Retrieved 6/7/01 from http: //www.barc.usda.gov:80/bhnrc/foodsurvey/pdf/Supp.pdf.

Acknowledgments The authors would like to thank the gym and the study participants for their cooperation. Thanks also goes to Alessandra Sarcona for her assistance.