Chrome 2001
Aetna Intelihealth InteliHealth Aetna Intelihealth Aetna Intelihealth
. .

Carepass Ad Carepass Ad .
Chrome 2001
Chrome 2001

Harvard Commentaries
Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School

Focus on Fitness Focus on Fitness

Can Nutritional Supplements Enhance Athletic Performance? (Part 2 of 2)

July 09, 2013

By Howard LeWine M.D.

Brigham and Women's Hospital



There are over 100 compounds advertised to be supplemental "ergogenic aids," substances you eat that improve your use of energy, increase energy production, or shorten the time needed to recover from exercise. Of these, only a few actually have any evidence to support their use as performance enhancers. But many are known to be dangerous or potentially harmful.

In Part 1, I discussed the ergogenic qualities of vitamins and minerals, amino acids and proteins, and carbohydrates. In general, compounds from these categories are relatively safe when taken in the prescribed dosages. Some of them do indeed improve performance if an athlete is not getting sufficient amounts from a balanced diet.

The other supplements do not have a dietary origin, and in fact act like drugs. But unlike prescription medications, the U.S. Food and Drug Administration (FDA) does not have the same regulatory control over supplements.

Back to top


Caffeine is the one compound with good scientific evidence to support its use as an athletic-performance enhancer. Taken in moderate doses, it's relatively safe. Caffeine is the only substance for which the International Olympic Committee (IOC) has set an acceptable level on urine samples, less than 12 micrograms per milliliter. A higher amount will bar an athlete from competition.

Caffeine's positive effect on athletic performance is most significant for endurance events such as long-distance running, cycling, and swimming. Normally, after 30 minutes of exertion glycogen (the body's most immediate source of glucose for energy) begins to deplete. Caffeine can slow the depletion of glycogen. At an intense pace, glycogen will not run out for one or two hours, but once it does, you can "hit the wall." By preserving glycogen stores longer, you can potentially increase your exercise time by 20%, or perhaps finish a race a little faster. The exact reason for this is under debate, but in some athletes caffeine stimulates earlier and greater use of fat burning for energy.

Performance in short-duration, high-intensity or strength events isn't enhanced by caffeine. The exception may be caffeine's central nervous system stimulation that might help in events requiring rapidly changing circumstances that need quick reactions and sudden alterations of body movements. On the other hand, you would want to avoid caffeine for events that require a steady hand.

The other potentially positive effects of caffeine for exercise include decreased awareness of feeling tired, mental alertness, and improvement in mood to help you maintain a workout program.

But caffeine definitely has its downside. There are important side effects of caffeine that can be quite detrimental to performance and if not attended to can be harmful. Performance-enhancing doses of caffeine cause you to urinate with greater frequency and with higher volumes. The diuretic action of caffeine needs to be balanced by drinking plenty of non-caffeinated beverages before, during, and after exercise. Some athletes get quite restless and nervous with any caffeine. Caffeine even in small amounts can cause insomnia.

The usual recommended caffeine dose is 250 to 500 milligram taken one hour before an event. I suggest starting at a dose in the lower range, about 300 milligrams, the amount in two cups of strong regular coffee, one to two hours before exercise. A person who never drinks coffee may need less, while someone who drinks two or more cups daily might need more.

Athletes required to provide urine testing must be very careful about how much caffeine they consume. Caffeine is present in many teas, sodas, chocolate, energy supplements, and over-the-counter medicines. The amount of caffeine can quickly add up and result in disqualification from competition. This is also good advice for any exercise enthusiast. Doses above those recommended can decrease performance.

Back to top

Ephedra (Ma Huang)

Ephedra and related compounds such as phenylpropanolamine, ephedrine, epinephrine, and phenylephrine don't enhance athletic performance nor do they provide any nutritional benefit. Ephedra-like substances stimulate the nervous system, increase heart rate and blood pressure, and speed up the metabolism. They are considered illegal substances by the IOC and National Collegiate Athletic Committee. Ephedra was banned by the FDA in December 2003. Athletes have died from taking amphetamine-like substances.

Drugs related to ephedra are used in asthma treatment, but even if prescribed can disqualify an athlete. Athletes with asthma competing at the highest levels need to inform the sports association of the medications they are taking. The athletes must be certain that none of their medications, including inhalers, is on the list of banned substances. Many of the over-the-counter asthma sprays contain banned substances.

If you have asthma but exercise non-competitively, good control of the condition with medications means more enjoyment of exercise and better performance.

Back to top


Despite the claims, "andro" (short for androstenedione) doesn't build muscle mass or enhance athletic performance. It may boost testosterone levels a bit, but most of the supplement is converted to the female hormone estrone, a form of estrogen. As an estrogen booster, andro can increase breast size (called gynecomastia). In addition, the supplement increases heart-attack risk, lowers HDL (good) cholesterol, and promotes acne. Over the long term, it can increase the size of the prostate gland. Andro is a banned substance for competition at the amateur level and also for many professional sports.

Back to top

DHEA (Dehydroepiandrosterone)

DHEA is a naturally occurring steroid made primarily in the adrenal glands. DHEA tends to fall as we age. It is still being studied in older men to determine if supplemental DHEA improves strength. However, DHEA isn't effective in improving athletic performance or strength training in people of any age. Side effects of DHEA are unknown. Because DHEA can be converted to testosterone and estrogen, DHEA may result in problems similar to those of andro.

Back to top

Coenzyme Q10

Coenzyme Q10 (Co Q10) is one of the key enzymes that are essential to energy production inside the body's cells. Within each cell, Coenzyme Q10 resides in the mitochondria, the powerhouse of aerobic metabolism. Since this is a natural energy booster inside all cells, it's easy to understand why people would be excited about a coenzyme Q10 supplement. But after many years of trying, scientists have been unable to show any performance-enhancing benefit when it is taken by mouth. Reports of side effects are rare.

Back to top

Howard LeWine, M.D., is chief editor of Internet publishing, Harvard Health Publications. He is a clinical instructor of medicine at Harvard Medical School and Brigham and Women's Hospital. Dr. LeWine has been a primary care internist and teacher of internal medicine since 1978.

More Focus on Fitness Articles arrow pointing right
    Print Printer-friendly format    
HMS header
 •  A Parent's Life
 •  Woman to Woman
 •  Focus on Fitness
 •  Medical Myths
 •  Healthy Heart
 •  Highlight on Drugs
 •  Food for Thought
 •  What Your Doctor Is Saying
 •  What Your Doctor Is Reading
 •  Minding Your Mind
 •  Man to Man

This website is certified by Health On the Net Foundation. Click to verify.