and vitamin C led to decreased endurance capacity within a few weeks. This decrease was most probably due to the deficiency in the B vitamins rather than vitamin C (see section on vitamin C).

Because deficiencies of several B vitamins will lead to performance decrements, it is reasonable to assume that supplementation with a combination of B vitamins would enhance performance. Several studies have evaluated the effects of vitamin B complex supplementation (an excellent and detailed review can be found in Williams, 1989). Using a controlled, crossover design, Keys and Henschel (1941) examined the effect of supplementation with 100 mg nicotinic acid amide, 5 mg thiamin chloride, and 100 mg ascorbic acid daily for 4 weeks. Subjects were eight infantry men, and the exercise test was a 15-minute submaximal treadmill test (marching) where the subjects carried a pack and rifle. Compared with the placebo, the supplementation did not result in improved physiological parameters during exercise. In a follow-up study, Keys and Henschel (1942) examined the effects of a supplement containing 5 to 17 mg thiamin, 10 mg riboflavin, 100 mg nicotinic acid, 10 to 100 mg vitamin B₆, 20 mg calcium pantothenate, and 100 to 200 mg ascorbic acid for 4 to 6 weeks. Subjects were 26 soldiers, and the exercise test was a strenuous treadmill run. Like their first study, Keys and Henschel found no beneficial effects on performance, so that endurance and resistance to fatigue were unaltered.

The effect of B complex supplementation on endurance capacity during a treadmill test was examined in physically active male college students (Read and McGuffin, 1983). The supplement contained 5 mg thiamin, 5 mg riboflavin, 25 mg niacin, 2 mg pyridoxine, 0.5 µg vitamin B₁₂, and 12.5 mg pantothenic acid. After 6 weeks of supplementation, there was no significant improvement in endurance capacity.

Early and Carlson (1969) suggested that vitamin B complex supplementation could enhance exercise in the heat because these water-soluble vitamins may be lost via sweating. They studied the effect of one dose of a vitamin B supplement, which contained 100 mg thiamin, 8 mg riboflavin, 100 mg niacinamide, 5 mg pyridoxine, 25 mg cobalamin, and 30 mg pantothenic acid. High school males were given either the supplement or a placebo 30 minutes before running 10 50-yard dashes during hot weather. The running times were recorded for each trial. The group that received the supplement showed less fatigue (drop-off in running time) over the trials. These authors suggested that the amount of supplement and the combination of ingredients may be important for a supplement to be effective. They stated that the lower dosages of vitamins used in previous studies may not have been adequate to fulfill the additional vitamin requirement because of sweat loss and heightened metabolic activity with exercise in the heat.

Henschel et al. (1944a) examined the effects of a supplement containing 200 mg ascorbic acid or 0.5 mg thiamin, 10 mg riboflavin, and 100 mg