The appropriate timing and provision of specific nutrients can help optimise training adaptations for men. Incorporating these principles as they age may also serve as an effective strategy to maintain strength, muscle mass and performance. Richard B Kreider, PhD, FACSM, investigates
As men get older, they notice a number of changes occurring in their bodies. They often lose muscle mass, gain fat and notice a decrease in strength, speed, agility and flexibility. They also notice that it takes longer to recover from exercise and recreational activities.
Additionally, they may discover that their cholesterol levels and other risk factors to chronic disease increase over time. As a result, many men become more interested in health, wellness and slowing the natural ageing process. Research has indicated that as men age, regular exercise and nutrition, including that directed toward performance-enhancement, can play an important role in optimising health and maintaining performance.
There are five basic components of health-related fitness: cardiovascular, muscular strength, muscular endurance, flexibility and body composition. It is well known that exercise can help slow down or prevent the normal declines in cardiopulmonary endurance, muscular strength, muscular endurance, flexibility and muscle mass that often occur as men age.1,2 The important point is that the more aerobic activity and resistance training is maintained as one gets older, the less loss is experienced in functional capacity.
Diet also plays an important role in maintaining health and slowing the normal ageing process. For active individuals, it is recommended by the American Diabetes Association that they consume a nutrient-dense, isocaloric, high-fibre diet consisting of 45?55 per cent complex carbohydrates (e.g., whole grains, legumes, fruits and vegetables), 10?15 per cent protein from quality sources (e.g., lean meat, fish, poultry and dairy products), and 25?30 per cent from fat (preferably low in saturated and trans-fatty acids).3 For individuals engaged in intense training, there is a greater need for carbohydrates and quality protein in the diet than by those who are more sedentary.4
Nutrition To Optimise Training And Performance
Research in sports nutrition has indicated that the appropriate timing and provision of specific nutrients can help optimise adaptations to training. For active men, incorporating these principles as they age may also serve as an effective strategy to maintain strength, muscle mass and performance. The following describes some basic nutritional principles used by athletes that may also help men maintain strength and muscle mass as they get older.
Creatine may be the most effective nutritional supplement available to help individuals increase high-intensity exercise capacity and muscle mass during training. Numerous studies have indicated that creatine supplementation increases body mass and muscle mass during resistance training. Gains are typically 2?5 pounds greater than controls during four to 12 weeks of training.5 The gains in muscle mass appear to be a result of an improved ability to perform high-intensity exercise that enables an athlete to train harder and thereby promote greater training adaptations and muscle hypertrophy.6
Because creatine supplementation has been found to increase strength and muscle mass, there has been interest in determining whether creatine may be beneficial in older populations. Most studies indicate that creatine supplementation in elder populations does lead to increased gains in strength and muscle mass.7,8 However, some studies show no effect.9,10 There also is evidence that creatine supplementation may decrease the incidence of injury during training,11 reduce muscle atrophy and facilitate rehabilitation following injury.12
The only clinically significant side effect reported from creatine supplementation has been weight gain.13 Although concerns have been raised about the safety and possible side effects of creatine supplementation,14 recent long-term safety studies have reported no apparent side effects.15,16 Consequently, for ageing men, creatine appears to be one of the best supplements available to help maintain strength, muscle mass and performance and may also be a way to slow or prevent age-related loss in muscle and strength as well.
Beta-hydroxy-beta-methylbutyrate (HMB) is a metabolite of the amino acid leucine. Leucine and meta-bolites of leucine have been reported to inhibit protein degradation.17 Supplementing the diet with 1.5?3g/day calcium HMB has been typically reported to increase muscle mass and strength, particularly amongst untrained subjects initiating training and older subjects.18,19 Gains in muscle mass are typically 0.5?1kg greater than controls during three to six weeks of training. There also is recent evidence that HMB may lessen the catabolic effects of prolonged exercise and that there may be additive effects of co-ingesting HMB with creatine.20,21
While the positive effects of HMB supplementation in untrained and older populations have been consistently reported, the effects of HMB supplementation in athletes are less clear. Most studies conducted on trained subjects have reported non-significant gains in muscle mass, possibly due to a greater variability in response of HMB supplementation amongst athletes.22,23
However, a recent meta-analysis concluded that creatine and HMB appear to be two effective nutritional supplements to enhance gains in strength and muscle mass during training.24 HMB supplementation appears to be safe and has been reported in one study to help reduce cholesterol.25 Consequently, HMB may be a supplement for men to consider as they get older.
Essential amino acids (EAA) ingested at 3?6g prior to and/or following exercise stimulate protein synthesis in both younger and older subjects.26,27,28,29,30,31 Theoret-ically, this may enhance gains in muscle mass during training.
In support of this theory, a recent study found that ingesting EAA with carbohydrates immediately following resistance exercise promoted significantly greater training adaptations in elderly men as compared to waiting until two hours after exercise to consume the supplement.32
Although more data are needed, there appears to be strong theoretical rationale and some supportive evidence that EAA supplementation may enhance protein synthesis and training adaptations. Ingestion of EAA following exercise may be a safe and effective nutritional strategy for men to maximise the benefits of exercise training in an attempt to maintain strength and muscle mass as they age. There are no health risks of ingesting 3?6g EAA, even in renal disease patients.
Glutamine is the most plentiful non-essential amino acid in the body and plays a number of important physiological roles.33 Glutamine has been reported to increase cell volume and stimulate protein and glycogen synthesis.34,35,36 Theoretically, the provision of 6?10g glutamine prior to and/or following exercise may help to optimise cell hydration and protein synthesis during training and can lead to greater gains in muscle mass and strength.33,37
In support of this hypothesis, researchers found that subjects who supplemented their diet with 5g/day glutamine and 3g/day branched-chain amino acid-enriched whey protein during training promoted about a two-pound greater gain in muscle mass and greater gains in strength than ingesting whey protein alone.38
There are data showing that patient populations and athletes have low glutamine levels and that supplementation of glutamine increases lymphocytic response to immune challenge and/or helps minimise the effects of intense exercise on the immune system.39 Theoretically, glutamine supplementation during training should enhance gains in strength and muscle mass as well as help athletes tolerate training to a better degree.
Carnitine is an important transporter of fatty acids from the cytosol into the mitochondria of the cell. Carnitine also protects the cell from acyl-CoA accretion through the generation of acylcarnitines.40 Carnitine supplementation has been theorised to improve exercise performance by enhancing muscle fatty acid oxidation, sparing muscle glycogen utilisation, altering glucose homeostasis, enhancing acylcarnitine production, improving training responses and delaying muscle fatigue.40 Carnitine supplementation also has been theorised to help decrease muscle trauma in response to periods of intensified training as well as help promote fat loss during training.
The available scientific evidence to support these theories is mixed. While there are some studies showing increased fat oxidation and/or weight loss, many studies show little ergogenic benefit from L-carnitine.41
A recent study has rekindled interest in L-carnitine as a nutritional supplement for active individuals.42 Researchers found that 2g/day L-carnitine for three weeks prior to performing six days of high-repetition squat exercise significantly reduced plasma markers of purine catabolism (hypoxanthine, xanthine oxidase and serum uric acid) and circulating cytosolic proteins (myoglobin, fatty acid-binding protein and creatine kinase).
In addition, plasma malondialdehyde—a marker of oxidative stress and cell damage— returned to resting values sooner and the amount of muscle disruption was 41?45 per cent lower when taking L-carnitine compared to the placebo.
The researchers concluded that L-carnitine supplementation was effective in assisting recovery from high-repetition squat exercise. For older individuals engaged in intense training, L-carnitine supplementation may help reduce exercise-induced muscle trauma.
Nutritional Promotion Of General Health In Active Men
Some nutrients may be particularly important for active individuals as they age. Some of these nutrients may help slow the ageing process and/or improve the health of the heart, bones, joints and endocrine system and bolster immunity. Unfortunately, this is necessarily a cursory treatment of these primary areas of concern for ageing individuals.
Antioxidants combat excessive elevations in reactive oxygen species and free radicals have been implicated as a possible contributing factor to ageing because they consume endogenous antioxidants and damage cells.43 Furthermore, intense exercise has been reported to increase free radical production and markers of oxidative stress.44 However, studies are equivocal whether chronic training affects antioxidant status.45
Nevertheless, nutritionists often recommend that older individuals, particularly if they are involved in intense exercise training, consume a diet rich in antioxidants such as vitamin C, vitamin E, selenium, beta-carotene and alpha-lipoic acid.46 Numerous studies indicate that, each and together, these antioxidants decrease markers of oxidative stress and muscle damage.47,48,49,50,51,52
While the majority of studies report no ergogenic effects of antioxidant supplementation on performance or training adaptations, several recent studies have reported some beneficial effects. For example, one recent double-blind study of 16 individuals reported that 150mcg selenium, 2,000IU retinol, 120mg ascorbic acid and 30IU alpha-tocopherol during tapered training reinforced antioxidant status response to exercise.53
Another study found that 1,200IU/day vitamin E during six days of intensified run training decreased markers of oxidative stress and muscle trauma.54
Finally, researchers in Spain found that vitamin C supplementation prior to performing a duathlon helped minimise exercise-induced increases in markers of oxidative stress and muscle damage.55
Several nutritional strategies are important to decrease risk to cardiovascular disease. For example, research suggests that people who maintain a diet low in saturated fat, trans-fatty acids, cholesterol and sodium are at a decreased risk for cardiovascular disease.56
Niacin supplementation has been reported to decrease total cholesterol in hyperlipidemic patients, particularly when combined with lipid-lowering statin medications.57 However, the beneficial effects of niacin supplementation on cholesterol levels may be negated to some degree in that niacin has also been reported to concomitantly increase homocysteine levels, which is a risk factor for heart disease.58
Vitamin E may decrease risk to initial and/or subsequent heart attacks.59 However, other studies have questioned this potential relationship.60 Because vitamin E is a good antioxidant, there may be health benefits from supplementing the diet with vitamin E even if there are no effects on risk to heart attacks.
Vitamin B12 and folate supplements may reduce homocysteine levels.61,62 However, some studies report no effects.63 Folate supplementation has also been reported to decrease risk of peripheral artery disease.64 One study found that supplementing the diet with a mixed fruit and vegetable concentrate high in antioxidants and folate lowered homocysteine levels.65
Omega-3 fatty acids, L-arginine, vitamin C and folic acid may bring about beneficial actions in various vascular diseases by enhancing endothelial nitric oxide production.66 However, additional research is needed to determine whether judicious combinations of these nutrients may serve as a novel approach to prevent and manage conditions such as hyperlipidemias, coronary heart disease, atherosclerosis, peripheral vascular disease and some neurodegenerative conditions.
Collectively, although much more research is needed, some evidence supports supplementation of niacin, vitamins C and E, folate, vitamin B12, omega-3 fatty acids and L-arginine to help decrease various risk factors associated with heart disease.
Bone And Joint Health
While loss of bone mass is typically thought to be more of a problem in females, older men also are susceptible to developing osteoporosis.67
Calcium and vitamin D have been reported to slow bone loss in both men and women.67 Maintaining adequate dietary availability of calcium is important to maintain bone mass.68 Consequently, ingesting an adequate amount of calcium and vitamin D in the diet may be an important strategy to maintain bone health as men age, particularly if they are undergoing androgen therapy for prostate cancer.69
Glucosamine and chondroitin have been reported to slow cartilage degeneration and reduce the degree of joint pain in active individuals.70,71 Glucosamine and chondroitin supplementation may be particularly helpful to slow cartilage degeneration in men who have old knee injuries. Collectively, dietary supplementation of calcium, glucosamine or chondroitin may help men maintain bone and joint health as they age.
Although glucosamine and chondroitin appear to be safe, people with glucose intolerance or diabetes should be counseled to check with their physician prior to taking these supplements.
The body naturally uses the androgen testosterone to stimulate the creation of protein throughout the body, especially in muscle. Testosterone is the most powerful regulator of muscle. Because androgens increase the building of contractile muscle proteins in the body, researchers believe they can help augment muscle mass that is lost during ageing.
Dehydroepiandrosterone (DHEA) and its sulfated conjugate DHEAS represent the most abundant adrenal steroids in circulation.72 Although DHEA is considered a weak androgen, it can be converted to the more potent androgens testosterone and dihydrotestosterone in tissues. In addition, DHEA can be converted into androstenedione and testosterone. DHEA levels have been reported to decline with age in humans.73 The decline in DHEA levels with ageing has been associated with increased fat accumulation and risk for heart disease.74
Because DHEA is a naturally occurring compound, it has been suggested that dietary supplementation of DHEA may help maintain DHEA availability, maintain and/or increase testosterone levels, reduce body fat accumulation and/or reduce risk to heart disease as one ages.72,74
Although animal studies have generally supported this theory, the effects of DHEA supplementation on body composition in human trials have been mixed. One randomised, double-blind study reported that 1,600mg/day DHEA for 28 days in five untrained healthy males promoted a 31 per cent reduction in percentage of body fat.75 Conversely, another study reported that 40mg/day DHEA for eight weeks had no effect on body weight, percent body fat or serum lipid levels in obese adolescents.76
Although more research is needed, these findings provide some support to contentions that DHEA and/or 7-keto DHEA may help maintain DHEA levels as one ages and be an effective weight-loss supplement, particularly in older individuals. However, additional research is needed before definitive conclusions can be made.
Prohormones such as androstenedione, 4-androstenediol, 19-nor-4-andro-stenedione and 19-nor-4-androstenediol are naturally derived precursors to testosterone. Prohormones have become popular amongst body builders because they are touted as natural testosterone boosters.
Although there is a strong theoretical rationale that prohormones may increase testosterone levels, there is virtually no evidence that these compounds affect training adaptations in younger men with normal hormone levels. In fact, most studies indicate that they do not affect testosterone and that some may actually increase estrogen levels and reduce HDL cholesterol.78,79,80
Since androgen levels decline as men age, there may be greater potential use of prohormones in older individuals to replace diminishing androgen levels. Over the last few years, studies have indicated that testosterone replacement in hyogonodal men can increase strength and muscle mass and can positively affect markers of health.81,82,83
Consequently, it is plausible that development of dietary prohormone supplements capable of maintaining or increasing testosterone levels may serve as viable nutritional means of replacing diminishing testosterone levels in hypogonodal men. However, additional research is necessary to test this hypothesis.
Exercise And Immunity
Moderate exercise improves immunity. However, intense exercise has been reported to increase susceptibility to upper respiratory-tract infections.84,85,86 For this reason, there has been interest in identifying ways to keep athletes healthy during intense training.
Carbohydrates, echinacea (Echinacea purpurea, E. angustifolia), glutamine, vitamin C and zinc have been the most extensively studied. Although more research is necessary, some evidence supports dietary supplementation of these nutrients to lessen the immunosuppressive effects of intense exercise and/or training.84,85,86,87 Consequently, some have recommended that athletes who feel a cold or an upper respiratory-tract infection coming on should supplement their diet with some of these nutrients. As intense exercise can suppress immune function in older individuals, use of these nutrients may help active ageing men stay healthy.
Richard B Kreider, PhD, FACSM, is Professor and Chair of the Department of Health, Human Performance and Recreation at Baylor University, Waco, Texas. Kreider has conducted more than 300 studies on nutrition and exercise including ones on carbohydrates, protein, amino acids, sodium phosphate, creatine, calcium HMB, conjugated linoleic acids (CLA), pyruvate, Coleus forskohli and various nutritional formulations designed to promote muscle hypertrophy and/or fat loss.
1. Kraemer WJ, et al. American College of Sports Medicine position stand. Progression models in resistance training for healthy adults. Med Sci Sports Exerc 2002;34(2):364.
2. Hass CJ, et al. Prescription of resistance training for healthy populations. Sports Med 2001;31(14):953.
3. Position of the American Dietetic Association: nutrition, ageing, and the continuum of care. J Am Diet Assoc 2000;100(5):580.
4. Kreider R, et al. Exercise and sport nutrition: A balanced perspective for exercise physiologists. Professionalization Exerc Physiol online 2003;6(8). Available: www.css.edu/users/tboone2/asep/balancedPerspective.pdf.
5. Kreider RB. Effects of creatine supplementation on performance and training adaptations. Mol Cell Biochem 2003;244(1-2):89.
6. Volek JS, et al. Performance and muscle fiber adaptations to 12 weeks of creatine supplementation and heavy resistance training. Med Sci Sport Exerc 1999;31(5).
7. Gotshalk LA, et al. Creatine supplementation improves muscular performance in older men. Med Sci Sports Exerc 2002;34(3):537.
8. Brose A, et al. Creatine supplementation enhances isometric strength and body composition improvements following strength exercise training in older adults. J Gerontol Series A Biol Sci 2003;58(1):11.
9. Bermon S, et al. Effects of creatine monohydrate ingestion in sedentary and weight- trained older adults. Acta Physiol Scand 1998;164(2):147.
10. Eijnde BO, et al. Effects of creatine supplementation and exercise training on fitness in males 55 to 75 years old. J Appl Physiol 2003 Aug;95(2):818-28. Epub 2003 Mar 28.
11. Watsford ML, et al. Creatine supplementation and its effect on musculotendinous stiffness and performance. J Strength Cond Res 2003;17(1):26.
12. Hespel P, et al. Oral creatine supplementation facilitates rehabilitation of disuse atrophy and alters expression of muscle myogenic factors in humans. J Physiol 2001;536(Pt 2):625.
13. Terjung RL, et al. American College of Sports Medicine roundtable. The physiological and health effects of oral creatine supplementation. Med Sci Sports Exerc 2000 Mar;32(3):706-17.
14. Juhn MS, Tarnopolsky M. Potential side effects of oral creatine supplementation: a critical review. Clin J Sport Med 1998;8(4):298.
15. Schilling BK, et al. Creatine supplementation and health variables: a retrospective study. Med Sci Sports Exerc 2001;33(2):183.
16. Kreider RB, et al. Long-term creatine supplementation does not significantly affect clinical markers of health in athletes. Mol Cell Biochem, In Press, 2003.
17. Nair KS, et al. Effect of leucine on amino acid and glucose metabolism in humans. Metabolism 1992;41(6):643.
18. Gallagher PM, et al. Beta-hydroxy-beta-methylbutyrate ingestion, Part I: effects on strength and fat free mass. Med Sci Sports Exerc 2000;32(12):2109.
19. Vukovich MD, et al. Body composition in 70-year-old adults responds to dietary beta-hydroxy-beta-methylbutyrate similarly to that of young adults. J Nutr 2001;131(7):2049.
20. Knitter AE, et al. Effects of beta-hydroxy-beta-methylbutyrate on muscle damage after a prolonged run. J Appl Physiol 2000;89(4):1340.
21. Jowko E, et al. Creatine and beta-hydroxy-beta-methylbutyrate (HMB) additively increase lean body mass and muscle strength during a weight-training program. Nutrition 2001;17(7-8):558.
22. Slater G, et al. Beta-hydroxy-beta-methylbutyrate (HMB) supplementation does not affect changes in strength or body composition during resistance training in trained men. Int J Sport Nutr Exerc Metab 2001;11(3):384.
23. Kreider R, et al. Effects of calcium B-HMB supplementation during training on markers of catabolism, body composition, strength and sprint performance. J Exerc Physiol Online 2000;3(4):48. Available: www.css.edu/users/tboone2/asep/dreiderFERREIRA.pdf.
24. Nissen SL, Sharp RL. Effect of dietary supplements on lean mass and strength gains with resistance exercise: a meta-analysis. J Appl Physiol 2003;94(2), 651.
25. Nissen S, et al. beta-hydroxy-beta-methylbutyrate (HMB) supplementation in humans is safe and may decrease cardiovascular risk factors. J Nutr 2000;130(8):1937.
26. Rasmussen BB, et al. An oral essential amino acid-carbohydrate supplement enhances muscle protein anabolism after resistance exercise. J Appl Physiol 2000;88(2):386.
27. Rasmussen BB, et al. Oral and intravenously administered amino acids produce similar effects on muscle protein synthesis in the elderly. J Nutr Health Aging 2002;6(6):358.
28. Miller SL, et al. Independent and combined effects of amino acids and glucose after resistance exercise. Med Sci Sports Exerc 2003;35(3):449.
29. Borsheim E, et al. Essential amino acids and muscle protein recovery from resistance exercise. Am J Physiol Endocrinol Metab 2002;283(4):E648.
30. Tipton KD, et al. Acute response of net muscle protein balance reflects 24-h balance after exercise and amino acid ingestion. Am J Physiol Endocrinol Metab 2003;284(1):E76.
31. Ferrando AA, et al. Differential anabolic effects of testosterone and amino acid feeding in older men. J Clin Endocrinol Metab 2003;88(1):358.
32. Esmarck B, et al. Timing of postexercise protein intake is important for muscle hypertrophy with resistance training in elderly humans. J Physiol 2001;535(Pt 1):301.
33. Kreider RB. Dietary supplements and the promotion of muscle growth with resistance exercise. Sports Med 1999;27(2):97.
34. Low SY, et al. Responses of glutamine transport in cultured rat skeletal muscle to osmotically induced changes in cell volume. J Physiol 1996;492 ( Pt 3):877.
35. Rennie MJ, et al. Amino acid transport in heart and skeletal muscle and the functional consequences. Biochem Soc Trans 1996;24(3):869.
36. Varnier M, et al. Stimulatory effect of glutamine on glycogen accumulation in human skeletal muscle. Am J Physiol 1995;269(2 Pt 1):E309.
37. Antonio J, Street C. Glutamine: a potentially useful supplement for athletes. Can J Appl Physiol 1999;24(1):1.
38. Colker CM. Effects of supplemental protein on body composition and muscular strength in healthy athletic male adults. Curr Ther Res 2000;61(1):19.
39. Rohde T, et al. Effect of glutamine supplementation on changes in the immune system induced by repeated exercise. Med Sci Sports Exerc 1998;30(6):856.
40. Brass EP. Supplemental carnitine and exercise. Am J Clin Nutr 2000;72(2 Suppl), 618S.
41. Gleim GG, Glace B. Carnitine as an ergogenic aid in health and disease. J Am Coll Nutr 1998;17(3):203.
42. Volek JS, et al. L-Carnitine L-tartrate supplementation favorably affects markers of recovery from exercise stress. Am J Physiol Endocrinol Metab 2002;282(2), E474.
43. Urso ML, Clarkson PM. Oxidative stress, exercise, and antioxidant supplementation. Toxicology 2003;189(1-2):41.
44. Chevion S, et al. Plasma antioxidant status and cell injury after severe physical exercise. Proc Natl Acad Sci USA 2003;100(9):5119.
45. Clarkson PM, Thompson HS. Antioxidants: what role do they play in physical activity and health? Am J Clin Nutr 2000;72(2 Suppl):S637.
46. Polidori MC. et al. Physical activity and oxidative stress during aging. Int J Sports Med 2000;21(3):154.
47. Appell HJ, et al. Supplementation of vitamin E may attenuate skeletal muscle immobilization atrophy. Int J Sports Med 1997;18(3):157.
48. Schroder H, et al. Effects of alpha-tocopherol, beta-carotene and ascorbic acid on oxidative, hormonal and enzymatic exercise stress markers in habitual training activity of professional basketball players. Eur J Nutr 2001;40(4):178.
49. Jakeman P and Maxwell, S., Effect of antioxidant vitamin supplementation on muscle function after eccentric exercise. Eur J Appl Physiol Occup Physiol 1993;67(5):426.
50. Avellini L, et al. Effect of exercise training, selenium and vitamin E on some free radical scavengers in horses (Equus caballus). Comp Biochem Physiol B Biochem Mol Biol 1999;123(2):147.
51. Khanna S, et al. Alpha-lipoic acid supplementation: tissue glutathione homeostasis at rest and after exercise. J Appl Physiol 1999;86(4):1191.
52. Henriksen EJ, Saengsirisuwan V. Exercise training and antioxidants: relief from oxidative stress and insulin resistance. Exerc Sport Sci Rev 2003;31(2):79.
53. Margaritis I, et al. Antioxidant supplementation and tapering exercise improve exercise-induced antioxidant response. J Am Coll Nutr 2003;22(2):147.
54. Itoh H, et al. Vitamin E supplementation attenuates leakage of enzymes following 6 successive days of running training. Int J Sports Med 2000;21(5):369.
55. Tauler P, et al. Influence of vitamin C diet supplementation on endogenous antioxidant defences during exhaustive exercise. Pflugers Arch 2003;446(6):658.
56. Dietary guidelines for healthy American adults. A statement for physicians and health professionals by the Nutrition Committee, American Heart Association. Circulation 1986;4(6):1465A.
57. Alaswad K, et al. Combination drug therapy for dyslipidemia. Curr Atheroscler Rep 1999;1(1):44.
58. Garg R, et al. Niacin treatment increases plasma homocyst(e)ine levels. Am Heart J 1999;138(6 Pt 1):1082.
59. Virtamo J, et al. Effect of vitamin E and beta carotene on the incidence of primary nonfatal myocardial infarction and fatal coronary heart disease. Arch Intern Med 1998;158(6):668.
60. Kritharides L, Stocker R. The use of antioxidant supplements in coronary heart disease. Atherosclerosis 2002;164(2):211.
61. de Bree A, et al. Coronary heart disease mortality, plasma homocysteine, and B-vitamins: a prospective study. Atherosclerosis 2003;166(2):369.
62. Neal B, et al. Dose-dependent effects of folic acid on plasma homocysteine in a randomized trial conducted among 723 individuals with coronary heart disease. Eur Heart J 2002;23(19):1509.
63. Hung J, et al. Folate and vitamin B-12 and risk of fatal cardiovascular disease: cohort study from Busselton, Western Australia. Brit Med J 2003;326(7381):131.
64. Merchant AT, et al., The use of B vitamin supplements and peripheral arterial disease risk in men are inversely related. J Nutr 2003;133(9):2863.
65. Samman S, et al. A mixed fruit and vegetable concentrate increases plasma antioxidant vitamins and folate and lowers plasma homocysteine in men. J Nutr 2003;133(7):2188.
66. Das UN. Folic acid says NO to vascular diseases. Nutrition 2003;19(7-8):686.
67. Gennari C. Calcium and vitamin D nutrition and bone disease of the elderly. Public Health Nutr 2001;4(2B):547.
68. Nordin BE, et al. Nutrition, osteoporosis, and aging. Ann NY Acad Sci 1998;854:336.
69. Ross RW, Small EJ. Osteoporosis in men treated with androgen deprivation therapy for prostate cancer. J Urol 2002;167(5):1952.
70. Braham R, et al. The effect of glucosamine supplementation on people experiencing regular knee pain. Br J Sports Med 2003;37(1):45.
71. Vad V, et al. Exercise recommendations in athletes with early osteoarthritis of the knee. Sports Med 2002;32(11):729.
72. Ebeling P, Koivisto VA. Physiological importance of dehydroepiandrosterone. Lancet 1994;343(8911):1479.
73. Denti L, et al. Effects of aging on dehydroepiandrosterone sulfate in relation to fasting insulin levels and body composition assessed by bioimpedance analysis. Metabolism 1997;46(7):826.
74. De Pergola G, et al. Body fat accumulation is possibly responsible for lower dehydroepiandrosterone circulating levels in premenopausal obese women. Int J Obes Relat Metab Disord 1996;20(12):1105.
75. Nestler JE, et al. Dehydroepiandrosterone reduces serum low density lipoprotein levels and body fat but does not alter insulin sensitivity in normal men. J Clin Endocrinol Metab 1988;66(1):57.
76. Vogiatzi MG, et al. Dehydroepiandrosterone in morbidly obese adolescents: effects on weight, body composition, lipids, and insulin resistance. Metabolism 1996;45(8):1011.
77. Kalman DS, et al. A randomized double-blind, placebo-controlled study of 3-acetyl-7-oxo-dehydroepiandrosterone in healthy overweight adults. Curr Thera 2000;61:435.
78. Broeder CE, et al. The Andro Project: physiological and hormonal influences of androstenedione supplementation in men 35 to 65 years old participating in a high-intensity resistance training program. Arch Intern Med 2000;160(20):3093.
79. Ballantyne CS, et al. The acute effects of androstenedione supplementation in healthy young males. Can J Appl Physiol 2000;25(1):68.
80. Brown GA, et al. Acute hormonal response to sublingual androstenediol intake in young men. J Appl Physiol 2002;92(1):142.
81. Szeszycki EE, Testosterone replacement increases fat-free mass and muscle size in hypogonadal men. JPEN J Parenter Enteral Nutr 1997;21(4):241.
82. Wang C, et al. Transdermal testosterone gel improves sexual function, mood, muscle strength, and body composition parameters in hypogonadal men. Testosterone Gel Study Group. J Clin Endocrinol Metab 2000;85(8):2839.
83. Testosterone replacement, weight lifting help wasting. Aids Alert 1996;11(6):suppl 1.
84. Nieman DC. Nutrition, exercise, and immune system function. Clin Sports Med 1999;18(3):537.
85. Nieman DC, Pedersen BK. Exercise and immune function. Recent developments. Sports Med 1999;27(2):73.
86. Shephard RJ, Shek PN. Immunological hazards from nutritional imbalance in athletes. Exerc Immunol Rev 1998;4:22.
87. Kasa, R.M., Vitamin C: from scurvy to the common cold. Am J Med Technol 1983;49(1):23.