Most vitamins serve as essential parts of enzymes or coenzymes that are vital to the metabolism of fats and carbohydrates (thus, they do not themselves yield energy, but are nutrients).

Extensive research has found little evidence to suggest that vitamin supplementation in well-fed athletes, eating a balanced diet has any benefits. However, people who are following a heavy programme of exercise may find that they develop a vitamin B1 (thiamin) deficiency, which is involved in CHO metabolism and Central Nervous System functioning. Excessive aerobic exercise can also lead to a vitamin C deficiency effecting connective tissue repair, iron absorption and the healing of infection. Heavy aerobic exercise or resistance training may elevate the need for vitamin B6 needed for protein metabolism and blood cell formation.

From the research it becomes clear that people exercising need to watch that their diet is well balanced and contains enough of the vitamins that may become deficient, so normal functioning is maintained.

Vitamins can be grouped into two categories (fat soluble and water soluble vitamins) according to the mediums they dissolve in (the types of foods that they are found in).

Vitamin Charts

Fat-Soluble vitamins

Vitamin	Main functions	Sources	Deficiency	Excess
A	Essential for vision in dim light; necessary for maintenance of mucous membranes, skin and growth	As retinol in milk, fortified margarine, butter, cheese, egg yolk, liver and fatty fish. As carotenes in milk, carrots, tomatoes, dark green vegetables	Reduced night vision; loss of sight through gradual damage to the cornea. Lowered resistance to infection	Vitamin A is stored in the liver and toxicity can occur
D	Promotes calcium and phosphate absorption from food and is thus essential for bones and teeth	Sunshine, fortified margarine, oily fish, egg yolk, fortified breakfast cereals	Failure of bones to grow and calcify leading to rickets in children and osteomalacia in adults	Vitamin D can be toxic
E	Protects cell membranes from damage by oxidation	Vegetable oils, nuts, vegetables and cereals	Deficiency may occur in premature infants or due to malabsorption	Not known
K	Essential in the formation of blood clotting proteins	Synthesis by bacteria in the gut. Dark green leafy vegetables, eg cabbage, brussel sprouts and spinach	Deficiency leads to an increased clotting time	Not known