All you need to know about 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.
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 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, is 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 discoloration of the skin might occur.
I remember experimenting 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 color. At the end of the month, there were some slight changes noticed, they 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 many 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 mother’s tale that eating carrots can help you to see in the dark, well this 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 mother’s advice and remember to eat your carrots!
Possible Additional Benefits of Vitamin A 1
· May reduce the risk of breast, lung, colon, prostate and cervical cancer
· May reduce the risk of heart disease and stroke
· May retard muscular degeneration (a common cause of blindness among the elderly)
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
The average daily intake level is sufficient to meet the nutritional requirements of nearly all (97-98%) healthy individuals in a particular life stage and gender group.
AI-Adequate Intake (used when an RDI cannot be determined)
The average daily nutrient intake level based on observed or experimentally-determined approximations or estimates of nutrient intake by a group (or groups) of apparently healthy people that are assumed to be adequate.