Vitamins are generally classified as water soluble or fat soluble, vitamins A, D, E and K are all fat soluble, which means that if not immediately used by the body they are absorbed and stored in fat tissue or the liver. This is important as if too much is stored, they can accumulate in your body and become toxic, this is very unlikely to occur if you eat a healthy, balanced diet. If you take supplements containing any of these you should take care that you are taking the correct recommended dose, this is especially important if taking multiple supplements, for example cod liver oil supplements also typically contain high levels of vitamin A, so should not be taken alongside any other supplementary sources.
The UK Government currently recommends the following individuals should supplement:
- Vitamins A, C and D: All children aged 6 months to 5 years
The UK recommended daily intake for vitamin A is 700 µg for men and 600 µg for women and should not exceed 1500 µg, research has shown that above this there is an increased risk of developing osteoporosis which is particularly important for menopausal women and the elderly (PHE, 2005). High levels of vitamin A can harm unborn babies, so it is advised that pregnant women do not take vitamin A supplements or consume liver/liver products such as pate as these contain very high levels.
Vitamin A is found in the body in three forms: retinol, retinal and retinoic acid and the precursors are carotenoids for example beta-carotene. Their major functions in the body are healthy vision by maintenance of the cornea, epithelial cells and mucosa of the eye and maintaining skin health by participating in protein synthesis and cell differentiation. Beta-carotene predominantly gets converted into vitamin A, but any leftover can function as an antioxidant, capable of protecting the body against disease, interestingly when taken in the form of a supplement research shows no benefit (Myung, 2010). This may be in part due to the dependence of the presence of other micronutrients, for example it is thought that vitamin A may control which bone-building genes respond to vitamin D and zinc is required for the synthesis of vitamin A’s retinol binding transport protein, this underlies the importance of eating a wide variety of nourishing foods daily (Whitney, 2011).
In order to meet daily vitamin A needs, try to include several servings of brightly coloured fruit and vegetables, beta-carotene is a yellow-orange compound and excellent sources include sweet potato, carrots, strawberries, oranges and pumpkin as well as dark leafy greens such as broccoli and spinach (the beta-carotene colour is masked by large amounts of green pigmented chlorophyll). Fast food is notoriously lacking in vitamin A, if consumed regularly it is advisable to increase the colourful fruit and vegetable content of other meals.
References
Public Health England, 2005 SACN Review of Dietary Advice on Vitamin A – GOV.UK
Myung, S.K et al, 2010. Effects of antioxidant supplements on cancer prevention: Meta-analysis of RCT. Annals of Oncology 21:166-179
Whitney, E et al, 2011. Understanding Nutrition: 2nd Edition
MLT Nutrition 