Vitamin C

Vitamin C functions as an antioxidant and is also involved in reactions that form the connective-tissue protein collagen. Fresh fruits and vegetables are the best sources of vitamin C. Meats and dairy products are low in vitamin C, and cereal grains contain none (unless fortified). Vitamin C is easily destroyed by cooking (heat) and exposure to air (oxygen). It is also highly water soluble, making it easily removed from foods cooked in water. The deficiency disease scurvy is almost nonexistent today. Toxicity from high, regular supplemental intakes of the vitamin is rare, but may include a predisposition to developing kidney stones and a reduction in tissue sensitivity to the vitamin. Doses of 100 to 200 milligrams per day will saturate the body with vitamin C,³³ yet many people take supplemental doses of 1,000 to 2,000 milligrams per day, well above the 75 to 90 milligrams per day of the DRI.

A number of studies have evaluated the relationship between vitamin C intake and athletic performance, although the results are inconsistent. Part of the problem with many of these studies is poor standardization between subjects and a general lack of comparative controls. Nevertheless, according to a review of studies that used controls and provided vitamin C supplements at or below 500 milligrams per day (remember that the DRI is 75 milligrams for adult women and 90 milligrams for adult men), there was no measurable benefit to athletic performance.³⁴ One study noted that when a 500-milligram dose of vitamin C was provided shortly (4 hours) before testing, there was a significant improvement in strength and a significant reduction in maximal oxygen consumption, but no impact on muscular endurance.³⁵ When subjects were provided with the same amount for 7 days, the result was an improvement in strength but a decrease in endurance. When these same subjectswere provided with 2,000 milligrams each day for 7 days, the athletes' VO₂max was lowered, but no change was evident in endurance performance.

Athletes involved in concussive sports-here muscle soreness occurs or an injury requires more collagen formation-may benefit from a slightly higher level of vitamin C. Studies on animals suggest that vitamin C improves the healing process, and inadequate vitamin C inhibits healing.³⁶ It has also been suggested that muscle soreness may be more rapidly relieved when consuming moderate supplemental doses of vitamin C and other antioxidants.³⁷

It is difficult to make a rational recommendation on vitamin C and performance, but athletes should keep the safe upper limit (2,000 milligrams per day) of this vitamin in mind before investing in supplements. Because some studies demonstrate that high doses may cause endurance problems, the intake level should be kept below the point of causing performance deficits. Vitamin C is known to enhance iron absorption. In 1993, there were three reported deaths due to iron overload, and the people who died were taking large daily doses of vitamin C.³⁸ Also consider that many athletes already consume more than 250 milligrams of vitamin C each day from food alone because of their high intake of fresh fruits and vegetables. A reasonable recommendation is to eat an abundant amount of fresh fruits and vegetables (wonderful sources of carbohydrate and many other nutrients besides vitamin C). If that's not possible, a reasonable strategy is to take a moderate daily supplement containing the DRI (between 75 and 90 milligrams per day). Except for athletes chronically consuming diets that are inadequate in energy, athletes meet the DRI and consume more vitamin C than the general nonathlete population.³⁹ Even someone consuming a low but regular intake of fruits and vegetables is likely to meet the DRI for vitamin C, but a low-level supplement may provide an appropriate safety buffer.