(That can cause problems in high doses)
Some supplements can benefit an athlete of any age if taken according to the manufacturers’ recommendations. For example, Vitamins and Mineral Supplements can benefit an athlete on a poor or weight-reducing diet who may not be getting enough vitamins and/or minerals through the diet. However, large doses of them can be toxic. For example, iron deficiency is relatively common in endurance athletes, particularly menstruating females, and directly affects performance by reducing the oxygen carrying capacity of the blood. However, megadoses of iron can create imbalances in other minerals such as copper because high iron intakes inhibit copper absorption in the gut. High levels of iron can also increase the risk of cardiovascular disease.
Creatine has been shown to benefit repeated sprint-performance in sports such as team sports where sprints are interspersed with rest or recovery periods of low intensity such as soccer, basketball or hockey. Athletes are recommended to load with 20-25 grams/day over 5 days then maintain with 1-2 grams/day to maximise the benefits. While not often taken in larger doses, in those people susceptible to kidney problems, the loading phase and regular use may be not recommended.
Kidney function may also be reduced in athletes taking in more than 2.8 grams/kg body weight/day of protein. Athletes are recommended protein dosages of between 0.8-1.6 grams/kg body weight/day with possible larger doses of 2.0 grams/kg body weight/day for masters athletes wanting to put on muscle mass via weight training.
Caffeine has been shown to legally enhance endurance performance with minimal side effects when used in dosages of 3-6 mg/kg body weight (one No-Doze tablet contains 100 mg caffeine). Higher dosages often result in nausea, dizziness, gut upsets and insomnia.