Retinol (Vitamin A)
Retinol, also known as Vitamin A is a generic description for at least 7 different active forms of the vitamin. As a fat soluble vitamin it is an important dietary component in the growth and repair of body tissues, boosting the immune system and in the maintenance of our eyes, skin, teeth, bones and mucous membranes. Vitamin A is also well known for its antioxidant properties and possesses antiviral, anti-carcinogenic and cardio-protective properties.
Vitamin A deficiencies are one of the most common vitamin deficiencies known. They are often seen in third world countries where malnutrition is a problem but are also seen in the top 5 nutrient deficiencies seen in children under the age of 5 in America. Deficiency in vitamin A can lead to a number of health related problems such as becoming more susceptible to infectious diseases particularly in the lung (eg pneumonia) and can also lead to blindness.
Despite vitamin A deficiencies being common, large doses of vitamin A in the form of retinol can also be toxic, particularly to pregnant women or people with liver impairments. As a fat soluble vitamin, the body stores retinol, where excessive consumption can lead retinol levels to accumulate to toxic levels within the body having detrimental health effects. It is believed that an estimated 5% of people who supplement with vitamin A unknowingly suffering from toxic symptoms which may include dry damaged skin and nails, nausea and vomiting.
Beta-Carotene (Provitamin A) is a precursor of vitamin A that the body breaks down into retinol as it needs to without creating toxic levels, for this reason it is safer to get your vitamin A in the form of beta-carotene. Beta carotene is also a more potent antioxidant than retinol which may help the body deal with oxidative stress and in particular has been found to be beneficial in the prevention and treatment of many cancers.
Given the implications of retinol toxicity it is suggested that if using supplementation that you look for supplements than provide vitamin A in the form of beta-carotene. Please refer to the chapter on nutritional supplements for more information.
One of our most commonly asked questions here at expert nutrition is whether large doses of beta-carotene are toxic?
The good news is that even high doses of beta carotene have not been shown to exhibit toxicity, even during pregnancy. However problems such as loose stools and a slight discolouration of the skin might occur.
I remember doing and experiment back when I was at university where we all had to eat lots (and lots) of carrots for a month to see if our skin would change colour. At the end of the month there were some slight changes noticed, they definitely didn't warn us about the loose stools until after the experiment was over, although we all noticed! In summary beta carotene is a much safer way to get your vitamin A as your body will only breakdown what it needs.
What are the best sources of Vitamin A?
Vitamin A can come from a number of sources including retinols which are found in animal products such as liver, most fish, eggs and dairy products and carotenoids which are found in plant based foods in particular those that have red or yellow pigments including most fruits and vegetables particularly carrots, pumpkin, spinach and sweet potato.
Remember the old mothers tale that eating carrots can help you to see in the dark, well this actually has an element of truth. Carrots are a good source of beta carotene which the body breaks down into retinol as it needs. The name retinol dates back to when vitamin A was first discovered to be beneficial to the retina found in the eye. In particular retinol plays an important role in maintaining the health of the rods, a part of the eye that is responsible for seeing low intensities of light and shades of grey. We now know that a deficiency in vitamin A commonly leads to night blindness, so take your mothers advice and remember to eat you carrots!
Possible Additional Benefits of Vitamin A 1
Recommended Dietary Intake for Vitamin A
A recent re-evaluation of dietary requirements for all vitamins and minerals was published by the National Health and Medical Research Council6. The dietary recommendations for Retinol from this publication are summarised below.
Please refer to the following definitions when interpreting these recommendations:
RDI-Recommended Daily Intake
AI-Adequate Intake (used when an RDI cannot be determined)
UL-Upper Limit of Intake
RECOMMENDATIONS BY LIFE STAGE AND GENDER Vitamin A
Source: National Health and Medical Research Council. Nutrient Reference Values for Australia and New Zealand. Department of Health and Ageing, Canberra 2006, copyright Commonwealth of Australia reproduced by permission.
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