VITAMIN A AND ITS BENEFITS FOR EXERCISE
Many key components of the body are dependent on vitamin A to maintain their function. This includes the respiratory system - obviously of prime importance in fitness training - our digestive tract linings, the uretha and bladder.
The different forms of vitamin A (retinoids and carotenoids) have varying functions within the body.
As an antioxidant, the carotenoids have been shown to have an important role in quenching free radical reaction.
It plays a role in immunity and the antibody response to infections.
It functions as an anti-inflammatory agent.
Research has demonstrated a link between red blood cell formation and vitamin A. As red blood cells utilise iron to transport oxygen around the body, anaemia is often found in those with a vitamin A deficiency, even though iron levels appear to be adequate. Anaemia can greatly impair athletic performance.
A sufficient supply of retinol is required to enable our eyes to adjust to low levels of light. Inadequate levels of vitamin A will result in night-blindness, hence the old adage that ‘carrots help you see in the dark’. The speed with which an individual becomes accustomed to the dark is an indication of vitamin A status.
Sufficient protein must be present in the diet for vitamin A to be delivered to the required cells within the body as it is transported to its target sites by attaching to a specific retinol-binding protein and a pre-albumin in the blood.
In the majority of cases foods that are derived from animals contain pre-formed vitamin A (retinol). This is easily hydrolysed in the intestine. Eggs, dairy products, liver and fish or fish oils are all good sources of vitamin A. Plant foods contain beta-carotene (a carotenoid). Sources can be found in carrots, dark green leafy vegetables, tomatoes, red peppers and broccoli. Fruits such as peaches, mangoes and apricots are also a good source. These pro-vitamins can also convert to retinol.
Unlike some other vitamins, cooking processes do not significantly harm retinol or carotenoids.
Clearly it is vital for an athlete to ensure that their intake of vitamin A is sufficient given that so many functions and processes within the body are reliant on carotenoids and retinoids. However, in excess vitamin A can be highly toxic. As vitamin A is fat soluble, excess levels will not be excreted in the urine, but will be stored in the liver. Hence the potential for toxicity and poisoning. Symptoms of high dosage include liver and bone damage, abdominal pain, dry skin, double vision, vomiting and hair loss.