It is a common myth that mega doses of vitamins improve athletic performance. Vitamin B needs do increase with vigorous activity, but these needs are easily met with an increase in caloric intake, which is needed with increased energy expenditure.
Iron deficiency can occur with vigorous exercise.
It can impair athletic performance by leading to accumulation of lactate in muscles and lactic acid buildup in muscles leads to muscle cramps. New studies show iron as an oxidant, having the opposite effect of antioxidants. 2- 4 hours before to allow for gastric emptying. A small 150 - 500 calorie meal of high carbohydrates is ideal. Seven simple carbohydrates taken immediately before or during prolonged exercise improves performance, however the immediate onset of exercise prevents hypoglycemia with the release of glucogen and catecholamines.