What are vitamins?

Micronutrients Do not supply energy Do not contribute to body mass Essential for metabolism Lack deficiency diseases Only vitamin D (some B-niacin; some K) can be

synthesised Others in the diet from plant sources (indirectly via

animals) sometimes as provitamins (e.g. carotene for Vitamin A).

disparate structure, related to lipids or carbohydrates 13 have been identified.

Vitamin B1 - Thiamin

• First vitamin to be discovered;• White rice consumption beriberi

– Neurological symptoms - fatigue, irritation, poor memory, sleep disturbances, anorexia, abdominal discomfort and constipation, burning sensations in the feet, calf muscle cramps and weakness.

– In 1890’s Dr. Eijkman noticed that chickens fed white rice developed similar symptoms. Chickens got better on brown rice

– Substance responsible not isolated until 1911 – an amine – called a vitamine

Water Soluble Vitamins.

Generally coenzymes (or their precursors) Bind with protein apoenzymes to produce the active enzyme Not stored Excess excreted in the urine Constant ingestion is necessary to avoid avitaminoses No serious hypervitaminoses.

Lipid Soluble Vitamins.

• stored in the liver (A, D, K) and adipose tissue (E)• do not need to be constantly ingested• can accumulate in excess.

• Hypervitaminosis A • teratogenic• bone swelling, weight loss and pruritis in children• nausea, anorexia, headache, brittle bones, alopecia and diarrhoea in adults.

• Hypervitaminosis D• kidney damage.

• Accidental excess supplementation in food processing • e.g. 4 cases in Boston, USA, 1992 after 500x excess added to milk.

• Supplementation with A and D must be with care!• Excess E and K is benign.

The Fat-Soluble Vitamins

Vit Significance Sources RDA Avitminosis Hypervitaminosis

A Maintains epithelia, Green and 1 mg Retarded growth, Liver damage, synthesis of yellow night blindness, skin peeling, visual pigments. vegetables. deterioration of CNS effects

epithelia. (nausea, anorexia).

D Bone growth, Sunlight, cod 10ug Rickets, Calcium deposits Ca & P absorption liver oil, dairy Osteomalacia. in tissues. at gut and kidneys. eggs, cornflakes! E Antioxidant. Meat, milk, 12 mg Anaemia. None reported. Protects vit A vegetables, & fatty acids. cereals.

K Hepatic synthesis Vegetables; 0.7- Bleeding Liver dysfunction, of prothrombin & intestinal 0.14 mg disorders. jaundice. other clotting factors. bacteria.

Vitamin A

• Vitamin A or retinol - immediate precursor to – retinal, critical role in

vision;– retinoic acid, intracellular

messenger that affects transcription of a number of genes.

• Many plants contain carotenoids such as beta-carotene that can be converted to vitamin A within tissues

Vitamin D

Biological function of vitamins

Uptake from gut.

Water soluble Diffusion. B12 by active transport with intrinsic factor.

Lipid soluble In micelles Transported in chylomicrons. Require dietary fats for absorption. Supplements must be taken with a meal.

To supplement or not to supplement?

• A balanced, non-vegan, diet supplies the RDA of all the vitamins

• No evidence for vitamins as ergogenic aids

• Megadoses (RDA x >10) of C may produce gout, haemolytic anaemia and GI upset.

• Megadoses of other vitamins can lead to hypervitaminoses

• Vitamin C supplementation may reduce the incidence of URTI infection in ultramarathon runners

• 30% of US adults use vitamin supplements

• Many sports scientists and free radical researchers hedge their bets

Vitamins as ergogenic aids.

Why do athletes commonly take vitamins? • They believe that megadoses will improve sports performance or enhance recovery.• They are concerned that prolonged marginal deficiency will compromise health and sports performance.• Higher RDA?

Most commonly supplemented vits – B’s , C, and E.

Do athletes get enough vitamins? •Increased energy intake associated with training, and a balanced diet, so athletes take an excess of vitamins. • Marginal vitamin deficiency may affect performance and has been detected in athletes with restricted food intakes. .

• Endurance training, (increased mitochondrial biogenesis and other metabolic adaptations) increases retention of vits E, C, B2 (riboflavin) and B6 (pyridoxine)?

Dietary antioxidants and exercise

• Radicals - molecules that possess an unpaired electron in outer shell/orbital

• Highly reactive and promote damaging oxidation reactions with cellular proteins, lipids or DNA oxidative stress (impaired cellular function)

• Exercise results in increased production of radicals (Davies et al., 1982)

• Primary source is mitochondria – 2-5% of oxygen undergoes 1 electron reduction superoxide radicals

Antioxidants

• Cells protected by – endogenous antioxidants eg. superoxide dismutase,

glutathione peroxidase and catalase;

– Exogenous dietary antioxidants eg. Vits E, C, carotenoids, flavenoids, ubiquinones (eg. Coenzyme Q)…

– Also trace minerals act as co-factors for antioxidant enzymes eg. Cu, Zn, Fe, Se, Mn

– Nb Vits C and β-carotene can function as both anti- and pro-oxidants

Homocysteine