Table of Contents:
- Types of Vitamin A
- Vitamin A Intake
- Functions of Vitamin A
A good balance of nutrients is required for overall good health but what happens if one of the nutrients is lacking?
Vitamin A is one of the fat soluble vitamins and so can be stored in the body, but a reduced intake or increased need may result in a deficiency which can have implications for health.
We always take an evidence-based approach and in this article we take a look at the importance of including adequate vitamin A in your diet.
There are a variety of forms of vitamin A and these can be split into two groups.
Preformed vitamin A comes from animal sources including oily fish such as tuna, mackerel, salmon, herring and trout and from liver, the dark meat from poultry, eggs and dairy products.
Provitamin A comes from specific carotenoids from fruits and vegetables that can be converted to an active form of vitamin A.
Not all carotenoids are converted to vitamin A but the ones that are include beta-carotene, alpha-carotene and beta-cryptoxanthin.
These are found in orange and green fruits and vegetables such as squash, pumpkin, peppers, sweet potato, carrots, broccoli, spinach and other dark green leafy vegetables.
A combination of both forms of vitamin A should be included in the diet regularly to ensure body stores are adequate.
If you are pregnant or breastfeeding there is an increased need for vitamin A, but care must be taken as vitamin A in excess has been linked to birth defects (1).
During conception and pregnancy provitamin A food sources can be useful as the body will convert these to active vitamin A when required.
Provitamin A is not linked with birth defects (2).
The tolerable upper safe limit for vitamin A has been set by the Scientific Committee on Food and the EFSA Scientific Panel on Dietetic Products, Nutrition and Allergies at 3000µg RE (10,000IU) for most adults.
Exceptions are post-menopausal women or those at high risk of bone fracture - for these the level is set at 1500µg RE (5000 IU) (3).
Studies have shown that high levels of vitamin A from diet or supplements may lead to a decrease in bone mineral density, this is thought to be due to vitamin A regulating gene expression involved in bone building and breakdown (4).
The same meta-analysis also found that a low intake of vitamin A also increased the risk of issues with bone density and fracture.
Perhaps the most well known function of vitamin A is its role in vision.
It is required for normal eye development during pregnancy (5) and also supports the function of the retina.
Within the retina, vitamin A is needed to support specialised dim light and colour receptor cells.
Therefore, a lack of vitamin A may impact dim light or colour vision.
The incidence of night blindness is common among populations that are more at risk of severe vitamin A deficiency.
The body has several natural barriers that act as a first line of defence including the skin, and the linings of the respiratory tract, urinary tract and gut.
Vitamin A aids in the maintenance of these natural barriers and so supports natural defences against infection or invasion.
It has also been found to have an immune modulatory effect and may enhance the outcome of particular vaccine programmes, such as measles (6).
It may also play a role in regulating the development of autoimmune disease (7).
Vitamin A is involved in the regulation of the growth and specialisation of almost all cells within the body.
It is heavily involved in regulation of gene expression, which may impact how the body uses information in the genes to make vital components like proteins.
Vitamin A has been shown to regulate several activities involved in cancer such as cell proliferation, differentiation and apoptosis (programmed cell death) (8,9), as well as promoting tumour suppressor genes.
Although vitamin A clearly has a role to play in prevention of cancer, currently there are no studies to indicate that increasing vitamin A intake to greater than the recommended daily amount is beneficial.
Despite the occurrence of birth defects when there is excess vitamin A intake during pregnancy, it is required to ensure healthy fertility and foetal development.
Vitamin A regulates gene expression for growth hormones and plays a role in the development and formation of the eyes, ears and heart.
Birth defects are also seen in cases of low vitamin A intakes.
Vitamin A seems to play a role in thyroid health and studies on animals indicate that a deficiency of vitamin A may disrupt the communication between the thyroid and the pituitary gland.
Animals who were deficient in vitamin A showed an increased production of thyroid stimulating hormone (TSH), increase in circulating thyroid hormones, a reduced uptake of iodine and an increase in the size of the thyroid (goitre) (10).
Restoring vitamin A and iodine in cases of deficiency significantly improves thyroid function and goitre (11).
Quite often these are pharmaceutical synthetic preparations of vitamin A given in very high doses and are linked with many side effects.
Like many nutrients, vitamin A plays a role in a myriad of functions within the body and maintaining an adequate intake is essential for overall body protection and health.
If you would like to know more about vitamin A and your health, advice from an Amchara Personalised Health practitioner may be beneficial.
We’re dedicated to providing you with both insightful information and evidence-based content, all orientated towards the Personalised Health approach.
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