In the competitive world of sports, the smallest advantage can make an enormous difference in the outcome of a contest. A supplement that could improve an athlete's strength, speed, or endurance could make the difference between tenth place and first place in a race. Supplements advocated for these purposes are discussed in the article Sports and Fitness Support: Enhancing Performance.

Supplements could conceivably play another helpful role for athletes: aiding recovery from the “side effects” of intense exercise. While exercise of moderate intensity is almost undoubtedly a purely positive activity, high-intensity endurance exercise, such as running marathons, can cause respiratory infections. In addition, all forms of exercise, when carried to the extremes, can cause severe muscle soreness, which may in turn get in the way of training. Herbs and supplements advocated for these problems are the subject of this article.

For information on natural treatments intended to aid recovery from injuries caused by sports, see the Sports Injury article.

According to a double-blind, placebo-controlled study involving 92 runners, taking 600 mg of vitamin C for 21 days prior to a race made a significant difference in the incidence of sickness afterwards.¹ Within 2 weeks after the race, 68% of the runners taking placebo developed symptoms of a common cold, versus only 33% of those taking the vitamin C supplement. As part of the same study, nonrunners of similar age and gender to those running were also given vitamin C or placebo. Interestingly, for this group, the supplement had no apparent effect on the incidence of upper respiratory infections. Vitamin C seemed to be specifically effective in this capacity for those who exercised intensively.

Two other studies found that vitamin C could reduce the number of colds experienced by groups of people involved in rigorous exercise in extremely cold environments.² One study involved 139 children attending a skiing camp in the Swiss Alps, while the other enrolled 56 military men engaged in a training exercise in Northern Canada during the winter months. In both cases, the participants took either 1 g of vitamin C or placebo daily at the time their training program began. Cold symptoms were monitored for 1 to 2 weeks following training, and significant differences in favor of vitamin C were found.

However, one very large study of 674 US Marine recruits in basic training found no such benefit.² The results showed no difference in the number of colds between the treatment and placebo groups.

What’s the explanation for this discrepancy? There are many possibilities. Perhaps basic training in the Marines is significantly different from the other forms of exercise studied. Another point to consider is that the Marines didn’t start taking vitamin C right at the beginning of training, but waited 3 weeks. The study also lasted a bit longer than the positive studies mentioned above—it continued for 2 months. Maybe vitamin C is more effective at preventing colds in the short term. Of course, another possibility is that it doesn’t really work. More research is needed to know for sure.

For more information, including dosage and safety issues, see the full Vitamin C article.

Like vitamin C, the amino acid glutamine may be helpful for preventing the infections that occur after severe exercise.

Glutamine is an important fuel source for some of our immune system cells. Some evidence suggests that athletes who have trained very hard have lower-than-normal levels of glutamine in their blood.³ One double-blind clinical trial involving 151 athletes found that supplementation with 5 g of glutamine immediately after heavy exercise, followed by another 5 g 2 hours later, reduced the incidence of infections quite significantly.⁴ Only 19% of those taking glutamine reported infections, while 51% of the placebo group succumbed to illness.

Probiotics are healthy organisms found in the digestive tract. Not only can they help preventive intestinal infections, they appear to help prevent colds as well. In a double-blind, controlled trial involving 20 healthy elite distance runners, researchers found that a probiotic supplement ( Lactobacillus fermentum) given over a 4-month period during winter training was significantly more effective at reducing the number and severity of respiratory symptoms compared to a placebo.²⁶

Weaker evidence suggests that beta-sitosterol might also offer some promise for this purpose.¹⁰

However, thymus extract, another proposed immune booster for athletes, does not seem to work, according to a double-blind, placebo-controlled trial of 60 athletes.⁵

Exercising increases the presence of free radicals, naturally occurring substances that can damage tissue. Some researchers have theorized that such damage may in part cause the muscle soreness, and perhaps muscle deterioration, that can accompany a strenuous workout.^6,7 Based on this theory, but little direct evidence, various antioxidants have been proposed to help prevent athletic muscle soreness or muscle damage including the following:

• Astaxanthin plus lycopene¹²
• Beta-carotene
• Cherry juice²¹
• Coenzyme Q₁₀
• Oligomeric proanthocyanidins (OPCs)
• Selenium
• Vitamin C
• Vitamin E

One double-blind trial compared vitamin C, vitamin E, and placebo for muscle soreness in 24 male volunteers.⁸ Vitamin C was found to relieve muscle soreness, while vitamin E did not. Two other studies failed to find vitamin C combined with vitamin E effective.^9,13-15 Another study failed to find benefit with the algae-derived carotenoid astaxanthin.¹⁶

One small double-blind study found that use of a mixed amino acid reduced muscle soreness caused by endurance exercising of the arm.²² These researchers actually performed two studies. The first involved simply taking the amino acid 30 minutes prior to exercising, and failed to find benefit. The second, more effective regimen added, in addition, one dose immediately after exercise and two doses daily for the next four days. In addition, a specific family of amino acids, BCAAs, have shown some promise for reducing muscle damage after long distance running.²⁴

The proteolytic enzyme supplement bromelain, used for sports injuries, has also been proposed for reducing muscle soreness after exercise. However, a double-blind, placebo-controlled trial that compared bromelain against placebo failed to find benefit.¹¹ Another study, this one using a mixed proteolytic enzyme supplement, also failed to find benefits.²⁵

Collagen hydrolysate is a nutritional supplement that may benefit cartilage tissue in joints. In a randomized, placebo-controlled study involving healthy college athletes with joint pain, 10 g daily of collagen hydrolysate appeared to effectively reduce the pain over a 24 week period.²⁷

The supplement phosphatidylserine has also failed to prove effective for reducing muscle soreness after exercise,¹⁷ as has chondroitin¹⁸ and magnet therapy.^19-20 In one study, the supplement glucosamine not only failed to prove effective for reducing exercise-induced muscle soreness, but actually increased it.²³

Athletes who train excessively may experience a condition called overtraining syndrome. Symptoms include depression, fatigue, reduced performance, and physiologic signs of stress. Numerous supplements have been suggested as treatments for this condition, most prominently antioxidants, and glutamine, but none have yet been proven effective.