Physical Education · Ch 5 — Sports and Nutrition
Vitamins
5.2.5
Vitamins
5.2.5 Vitamins
Vitamins are chemicals the body needs in small amounts to work properly. They act in many ways, mostly as 'helpers' — for example, many of the B-vitamins help the body use protein, fats and carbohydrates.
Vitamins fall into two categories:
- Water-soluble vitamins — all the B vitamins and vitamin C. Any amount the body does not use passes through the kidneys and leaves in urine or stool, so the body needs these in frequent small doses; they are unlikely to reach toxic levels.
- Fat-soluble vitamins — vitamins A, D, E and K. These are stored in the body's cells and are not passed out as easily as water-soluble vitamins, so they are more likely to reach toxic levels if taken in excess.
The two tables below list the water-soluble and fat-soluble vitamins, their important functions, and the foods that supply them.
Table 2.i — Water-soluble vitamins
| Nutrient | Important functions | Sources |
|---|---|---|
| Thiamine (vitamin B1) | • Works as the coenzyme thiamine pyrophosphate (TPP), needed for energy metabolism • Important for nerve function • Needed for DNA and RNA synthesis | Whole-grain cereals, pulses, peanuts and seeds, mushrooms, green peas, beans, egg yolk and meat |
| Riboflavin (vitamin B2) | • Acts as two coenzymes, FMN and FAD, needed for energy metabolism • Important for normal vision and skin health | Milk and milk products; eggs, liver, kidney; green leafy vegetables such as broccoli; whole-grain cereals; legumes |
| Niacin (vitamin B3) | • Part of the coenzymes NAD and NADP, needed for energy metabolism • Important for the nervous system, digestive system and skin | Whole-grain cereals, pulses, meat, poultry, fish, vegetables (especially mushrooms). Eggs, milk and milk products lack niacin but are rich in the EAA tryptophan, which the body can convert to niacin (60 mg tryptophan yields 1 mg niacin) |
| Vitamin B6 (pyridoxal, pyridoxine and pyridoxamine) | • Part of the coenzyme pyridoxal phosphate, needed for protein and amino-acid metabolism and involved in many enzymes for carbohydrate, fat and protein metabolism • Helps make white blood cells and heme in haemoglobin | Meat, poultry, fish, nuts, sunflower seeds, pulses, whole grains, spinach, bananas, potatoes |
| Biotin | • Functions as a coenzyme in metabolic reactions | Widespread in foods: organ meats (liver, kidney), egg yolk, nuts (almonds, peanuts, walnuts), soybeans and other legumes, whole grains, bananas, cauliflower, mushrooms; also produced by bacteria in the intestinal tract |
| Pantothenic acid | • Part of coenzyme A (CoA), needed for energy metabolism | Widespread in foods: milk, meat, peanuts, eggs |
| Folic acid / Folate | • Part of an enzyme needed for making DNA and new cells, especially red blood cells • Formation of neurotransmitters • Needed to maintain normal blood pressure and reduce cancer risk | Green leafy vegetables (especially spinach), pulses, oranges and orange juice, and liver; also cabbage, cauliflower and broccoli |
| Cobalamin (vitamin B12) | • Part of two coenzymes, methylcobalamin and 5-deoxyadenosylcobalamin, needed for making new cells • Important for nerve function | Meat, poultry, fish, seafood, eggs, milk and milk products; not found in plant foods |
| Ascorbic acid (vitamin C) | • Antioxidant; role in collagen formation and so in wound healing; part of an enzyme needed for protein metabolism • Important for the immune system and helps iron absorption | Fruits and vegetables, especially citrus fruits, fresh vegetables of the cabbage family, sprouts, amla and guava |
Table 2.ii — Fat-soluble vitamins
Fat-soluble vitamins are stored in the body's cells and are not excreted as easily as water-soluble ones, so taking them in high amounts can become toxic; a balanced diet usually supplies enough.
| Nutrient | Important functions | Sources |
| --- | --- | --- | …