1 What are they?
Vitamin A is a vitamin that comes in two forms: retinol and the provitamin beta-carotene (which we convert to vitamin A). Beta-carotene is one of the 600 different carotenoids which are found in plants; approximately 20 of these have been found in human blood and tissues. They are believed to provide protection to both plants and humans. Carotenoids give fruit and vegetables their red, orange, yellow colours.
You may also be familiar with the names lutein and lycopene.
2 How do vitamin A and carotenoids work as antioxidants?
In general, carotenoids are believed to scavenge free radicals, as well as helping to reduce the highly reactive oxygen molecules that form some free radicals. One type of carotenoids known as xanthophylls, help to protect against damage from sunlight and protect eye health. They have also been found to have roles in the immune system (including allergies), bone health and the nervous system.
Retinol is thought to have two potential antioxidant benefits: it reacts and combines with free radicals preventing them damaging cells (“scavenging”); and regulates nitric oxide production in various tissues, including the heart cells. While nitric oxide acts as a free radical, it is also thought to have antioxidant properties, lower blood pressure and improve blood supply around the body.
3 Where in the body do we find carotenoids?
Because carotenoids are fat-soluble we store excess nutrients within the body until they are needed, unlike with excess water-soluble nutrients which we excrete.
The highest levels of carotenoids are found in the liver and body fat. However, high levels have also been found in the adrenal glands, eyes, skin, testes and corpus luteum (a temporary structure formed during ovulation and pregnancy).
4 Sources
Vitamin A (retinol) can be found in dairy products, oily fish and liver.
Carotenoids can be found in plants such as carrots, tomatoes, green leafy vegetables, squash, avocados and cantaloupe melon. They are also available from egg yolks.
NOTE: individuals who smoke should avoid taking supplements containing beta-carotene as it may increase their risk of developing lung cancer.
5 Absorption
Unlike many of our nutrients, we are often able to utilise carotenoids better after they have been prepared and cooked.
Sources of carotenoids are best consumed alongside healthy fats, if they don’t already contain fat, as they are fat-soluble. However, health conditions which affect people’s absorption of fats may interfere with their absorption of the carotenoids. Some medications (for example aspirin) may also reduce absorption of beta-carotene. If you have any concerns about nutrient absorption in relation to medication, do not change your medications without prior consultation with your doctor!
References/Further Reading
- Potential Role of Carotenoids as Antioxidants in Human Health and Disease – Fiedor and Burda. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3942711/
