Definition and Regulation of Dietary Supplements
Product Development and Quality Assurance
Evaluation of Nutritional Ergogenic Aids
Does The Theory Make Sense?
Is There Any Scientific Evidence Supporting The Ergogenic Value?
Are the studies basic research done in animals/clinical populations or have the studies been conducted on athletes/trained subjects? Studies reporting improved performance in rats or persons with type 2 diabetes may be insightful but research conducted on non-diabetic athletes is much more practical and relevant.
Were the studies well controlled? For ergogenic aid research, the study should be a placebo controlled, double-blind, and randomized clinical trial if possible. This means that neither the researcher's nor the subject's were aware which group received the supplement or the placebo during the study and that the subjects were randomly assigned into the placebo or supplement group. An additional element of rigor is called a cross-over design, where each subject, at different times (separated by an interval known as a "washout period"), is exposed to each of the treatments. While utilization of a cross-over design is not always feasible, it removes the element of variability between subjects and increases the strength of the findings. At times, supplement claims have been based on poorly designed studies (i.e., small groups of subjects, no control group, use of unreliable tests, etc) and/or testimonials which make interpretation much more difficult. Well-controlled clinical trials provide stronger evidence as to the potential ergogenic value.
Do the studies report statistically significant results or are claims being made on non-significant means or trends reported? Appropriate statistical analysis of research results allows for an unbiased interpretation of data. Although studies reporting statistical trends may be of interest and lead researchers to conduct additional research, studies reporting statistically significant results are obviously more convincing. With this said, a sports nutrition specialist must be careful not to commit type II statistical errors (i.e., indicating that no differences were observed when a true effect was seen but not detected statistically). Since many studies on ergogenic aids (particularly in high level athletes) evaluate small numbers of subjects, results may not reach statistical significance even though large mean changes were observed. In these cases, additional research is warranted to further examine the potential ergogenic aid before conclusions can be made.
Do the results of the studies cited match the claims made about the supplement? It is not unusual for marketing claims to greatly exaggerate the results found in the actual studies. Additionally, it is not uncommon for ostensibly compelling results, that may indeed by statistically significant, to be amplified while other relevant findings of significant consumer interest are obscured or omitted (e.g. a dietary supplement showing statistically significant increases in circulating testosterone yet changes in body composition or muscular performance were not superior to a placebo). The only way to determine this is to read the entire article, and not just the abstract or even the article citation, and compare results observed in the studies to marketing claims. Reputable companies accurately and completely report results of studies so that consumers can make informed decisions about whether to try a product or not.
Were results of the study presented at a reputable scientific meeting and/or published in a peer-reviewed scientific journal? At times, claims are based on research that has either never been published or only published in an obscure journal. The best research is typically presented at respected scientific meetings and/or published in reputable peer-reviewed journals. Two ways to determine a journal's reputation is either identifying the publisher or the "impact factor" of the journal. A number of "peer-reviewed" journals are published by companies with ties to, or are actually owned by, nutritional products companies (even though they may be available on PubMed). Therefore, we recommend looking up the publisher's website and see how many other journals they publish. If you see only a few other journals this is a suggestion that the journal is not a reputable journal. Alternatively, inquire about the impact factor, a qualitative ranking determined by the number of times a journal's articles are cited. Impact factors are determined and published by Thomson Reuters under Journal Citation Reports® (a subscription service available at most university libraries). Most journals list their impact factor on the journal home page. The most significant and erudite scientific articles are typically the most read and the most cited.
Have the research findings been replicated at several different labs? The best way to know an ergogenic aid works is to see that results have been replicated in several studies preferably by a number of separate, distinct research groups. The most reliable ergogenic aids are those in which a number of studies, conducted at different labs, have reported similar results of safety and efficacy. Additionally, replication of results by different, unaffiliated labs with completely different authors also removes or reduces the potentially confounding element of publication bias (publication of studies showing only positive results) and conflicts of interest. A notable number of studies on ergogenic aids are conducted in collaboration with one or more research scientists or co-investigators that have a real or perceived economic interest in the outcome of the study. This could range from being a co-inventor on a patent application that is the subject of the ergogenic aid, being paid or receiving royalties from the creation of a dietary supplement formulation, or having stock options or shares in a company that owns or markets the ergogenic aid described in the study. An increasing number of journals require disclosures by all authors of scientific articles, and including such disclosures in published articles. This is driven by the aim of providing greater transparency and research integrity. Disclosure of a conflict of interest does not alone discredit or dilute the merits of a research study. The primary thrust behind public disclosures of potential conflicts of interest is the prevention of a later revelation of an interest that has the potential of discrediting the study in question, the authors, and even the research center or institution where the study was conducted.
Is The Supplement Legal And Safe?
Classifying and Categorizing Supplements
General Dietary Guidelines for Active Individuals
Strategic Eating and Refueling
Proposed Ergogenic Value
Summary of Research Findings
Males 900 mcg/d Females 700 mcg/d
Constituent of rhodopsin (visual pigment) and is involved in night vision. Some suggest that vitamin A supplementation may improve sport vision.
No studies have shown that vitamin A supplementation improves exercise performance .
5 mcg/d (age <51)
Promotes bone growth and mineralization. Enhances calcium absorption. Supplementation with calcium may help prevent bone loss in osteoperotic populations.
As an antioxidant, it has been shown to help prevent the formation of free radicals during intense exercise and prevent the destruction of red blood cells, improving or maintaining oxygen delivery to the muscles during exercise. Some evidence suggests that it may reduce risk to heart disease or decrease incidence of recurring heart attack.
Numerous studies show that vitamin E supplementation can decrease exercise-induced oxidative stress [482–484]. However, most studies show no effects on performance at sea level. At high altitudes, vitamin E may improve exercise performance . Additional research is necessary to determine whether long-term supplementation may help athletes better tolerate training.
Males 120 mcg/d Females 90 mcg/d
Important in blood clotting. There is also some evidence that it may affect bone metabolism in postmenopausal women.
Vitamin K supplementation (10 mg/d) in elite female athletes has been reported to increase calcium-binding capacity of osteocalcin and promoted a 15-20% increase in bone formation markers and a 20-25% decrease in bone resorption markers suggesting an improved balance between bone formation and resorption .
Males 1.2 mg/d Females 1.1 mg/d
Coenzyme (thiamin pyrophosphate) in the removal of CO2 from decarboxylic reactions from pyruvate to acetyl CoA and in TCA cycle. Supplementation is theorized to improve anaerobic threshold and CO2 transport. Deficiencies may decrease efficiency of energy systems.
Dietary availability of thiamin does not appear to affect exercise capacity when athletes have a normal intake .
Males 1.3 mg/d Females 1.7 mg/d
Constituent of flavin nucleotide coenzymes involved in energy metabolism. Theorized to enhance energy availability during oxidative metabolism.
Dietary availability of riboflavin does not appear to affect exercise capacity when athletes have a normal intake .
Males 16 mg/d Females 14 mg/d
Constituent of coenzymes involved in energy metabolism. Theorized to blunt increases in fatty acids during exercise, reduce cholesterol, enhance thermoregulation, and improve energy availability during oxidative metabolism.
Studies indicate that niacin supplementation (100-500 mg/d) can help decrease blood lipid levels and increase homocysteine levels in hypercholesteremic patients [488, 489]. However, niacin supplementation (280 mg) during exercise has been reported to decrease exercise capacity by blunting the mobilization of fatty acids .
1.3 mg/d (age <51)
Has been marketed as a supplement that will improve muscle mass, strength, and aerobic power in the lactic acid and oxygen systems. It also may have a calming effect that has been linked to an improved mental strength.
A coenzyme involved in the production of DNA and serotonin. DNA is important in protein and red blood cell synthesis. Theoretically, it would increase muscle mass, the oxygen-carrying capacity of blood, and decrease anxiety.
In well-nourished athletes, no ergogenic effect has been reported. However, when combined with vitamins B1 and B6, cyanocobalamin has been shown to improve performance in pistol shooting . This may be due to increased levels of serotonin, a neurotransmitter in the brain, which may reduce anxiety.
Folic acid (folate)
Functions as a coenzyme in the formation of DNA and red blood cells. An increase in red blood cells could improve oxygen delivery to the muscles during exercise. Believed to be important to help prevent birth defects and may help decrease homocysteine levels.
Studies suggest that increasing dietary availability of folic acid during pregnancy can lower the incidence of birth defects . Additionally, it may decrease homocysteine levels (a risk factor for heart disease) . In well-nourished and folate deficient-athletes, folic acid did not improve exercise performance .
Acts as a coenzyme for acetyl coenzyme A (acetyl CoA). This may benefit aerobic or oxygen energy systems.
Research has reported no improvements in aerobic performance with acetyl CoA supplementation. However, one study reported a decrease in lactic acid accumulation, without an improvement in performance .
Serves as an antioxidant. Theorized to help minimize exercise-induced lipid peroxidation and muscle damage.
Research indicates that beta carotene supplementation with or without other antioxidants can help decrease exercise-induced peroxidation. Over time, this may help athletes tolerate training. However, it is unclear whether antioxidant supplementation affects exercise performance .
Males 90 mg/d Females 75 mg/d
Used in a number of different metabolic processes in the body. It is involved in the synthesis of epinephrine, iron absorption, and is an antioxidant. Theoretically, it could benefit exercise performance by improving metabolism during exercise. There is also evidence that vitamin C may enhance immunity.
In well-nourished athletes, vitamin C supplementation does not appear to improve physical performance [497, 498]. However, there is some evidence that vitamin C supplementation (e.g., 500 mg/d) following intense exercise may decrease the incidence of upper respiratory tract infections [471, 499, 500].
Proposed Ergogenic Value
Summary of Research Findings
Boron has been marketed to athletes as a dietary supplement that may promote muscle growth during resistance training. The rationale was primarily based on an initial report that boron supplementation (3 mg/d) significantly increased β-estradiol and testosterone levels in postmenopausal women consuming a diet low in boron.
Studies which have investigated the effects of 7 wk of boron supplementation (2.5 mg/d) during resistance training on testosterone levels, body composition, and strength have reported no ergogenic value [171, 172]. There is no evidence at this time that boron supplementation during resistance-training promotes muscle growth.
1000 mg/d (ages 19-50)
Involved in bone and tooth formation, blood clotting, and nerve transmission. Stimulates fat metabolism. Diet should contain sufficient amounts, especially in growing children/adolescents, female athletes, and postmenopausal women . Vitamin D needed to assist absorption.
Males 35 mcg/d Females 25 mcg/d (ages 19-50)
Chromium, commonly sold as chromium picolinate, has been marketed with claims that the supplement will increase lean body mass and decrease body fat levels.
Animal research indicates that chromium supplementation increases lean body mass and reduces body fat. Early research on humans reported similar results , however, more recent well-controlled studies reported that chromium supplementation (200 to 800 mcg/d) does not improve lean body mass or reduce body fat [176, 180].
Males 8 mg/d Females 18 mg/d (age 19-50)
Iron supplements are used to increase aerobic performance in sports that use the oxygen system. Iron is a component of hemoglobin in the red blood cell, which is a carrier of oxygen.
Most research shows that iron supplements do not appear to improve aerobic performance unless the athlete is iron-depleted and/or has anemia .
Males 420 Females 320
Activates enzymes involved in protein synthesis. Involved in ATP reactions. Serum levels decrease with exercise. Some suggest that magnesium supplementation may improve energy metabolism/ATP availability.
Phosphorus (phosphate salts)
Phosphate has been studied for its ability to improve all three energy systems, primarily the oxygen system or aerobic capacity.
Recent well-controlled research studies reported that sodium phosphate supplementation (4 g/d for 3 d) improved the oxygen energy system in endurance tasks [400–402]. There appears to be little ergogenic value of other forms of phosphate (i.e., calcium phosphate, potassium phosphate). More research is needed to determine the mechanism for improvement.
An electrolyte that helps regulate fluid balance, nerve transmission, and acid-base balance. Some suggest excessive increases or decreases in potassium may predispose athletes to cramping.
Although potassium loss during intense exercise in the heat has been anecdotally associated with muscle cramping, the etiology of cramping is unknown [505, 506]. It is unclear whether potassium supplementation in athletes decreases the incidence of muscle cramping . No ergogenic effects reported.
Marketed as a supplement to increase aerobic exercise performance. Working closely with vitamin E and glutathione peroxidase (an antioxidant), selenium may destroy destructive free radical production of lipids during aerobic exercise.
An electrolyte that helps regulate fluid balance, nerve transmission, and acid-base balance. Excessive decreases in sodium may predispose athletes to cramping and hyponatremia.
During the first several days of intense training in the heat, a greater amount of sodium is lost in sweat. Additionally, prolonged ultraendurance exercise may decrease sodium levels leading to hyponatremia. Increasing salt availability during heavy training in the heat has been shown to help maintain fluid balance and prevent hyponatremia [64, 509].
Vanadyl sulfate (vanadium)
Vanadium may be involved in reactions in the body that produce insulin-like effects on protein and glucose metabolism. Due to the anabolic nature of insulin, this has brought attention to vanadium as a supplement to increase muscle mass, enhance strength and power.
Males 11 mg/d Females 8 mg/d
Constituent of enzymes involved in digestion. Associated with immunity. Theorized to reduce incidence of upper respiratory tract infections in athletes involved in heavy training.
Dietary Supplements and Athletes
Muscle Building Supplements
Muscle Building Supplements
Weight Loss Supplements
Apparently effective and generally safe
Weight gain powders
Low-calorie foods, MRPs, and RTDs
Ephedra, caffeine, and salicin-containing thermogenic supplements taken at recommended doses in appropriate populations (ephedra banned by FDA)
Water and sports drinks
HMB (untrained individuals initiating training)
Green tea extract
Conjugated Linoleic Acids
Post-exercise carbohydrate & protein
Too early to tell
Growth hormone releasing peptides and secretogues
Gymnema sylvestre, chitosan)
Medium chain triglycerides
Apparently not effective and/or dangerous
Sulfo-polysaccharides (myostatin inhibitors)
Conjugated linoleic acids
Vanadyl sulfate (vanadium)