A Fundamental Breakdown: Vitamin A

Introduction

As mentioned in a previous post, we will be releasing articles on each micronutrient over time, detailing their role in the body, the recommended intake level given by various regions and the Upper Tolerable Limit, what symptoms may occur if you are getting too little (a deficiency) or too much (a toxicity), as well as the forms and amounts we use in our products. These posts will be released in the same order as nutrients are listed on the EU nutrition table. 

As with previous posts, these will be displayed as a brief, bolded statement which gives the basic information, followed by a more complex, unbolded explanation.

Today’s post will be on the first of these nutrients - vitamin A.

Role of vitamin A

Vitamin A supports cell growth and health, immune function and vision. Cell growth and health is aided by vitamin A acting as an antioxidant to prevent damage from harmful, reactive cells. Vitamin A is involved in the production of different white blood cells, supporting the immune response. Finally, vitamin A aids vision by forming a molecule that generates electrical signals that stimulate the visual cortex in the brain.

Vitamin A is an antioxidant, which means they ‘fight’ free radicals in the body. Free radicals are highly reactive molecules that can cause damage to cells and DNA due to their reactivity. They can cause cell damage via what is known as oxidative stress. As the term “antioxidant” implies, they ‘fight’ against the oxidative free radicals by reacting with them, nullifying their ability to cause cellular damage and inhibit healthy cell division and growth. Leaving these free radicals in the body to cause oxidative damage to DNA can lead to the formation of cancers, so this is a particularly vital role of vitamin A. Oxidative stress has also been linked to other chronic diseases, like diabetes, heart disease and cognitive decline, so ensuring an adequate intake of vitamin A is very important. 

Vitamin A also goes beyond just this, though, in terms of immune function. Vitamin A is a key component in the creation of B- and T-cells (bone-marrow cells and thymus cells respectively), which are very heavily involved in our immune system. Our immune response is very complex, but at a simple level it involves the actions of different types of these B- and T-cells. B-cells are the main cells involved in the production of antibodies for fighting off diseases, while T-cells are involved in inducing the death of cells that have been infected with viruses, or are dysfunctional or damaged for other reasons. Without these cells, various pathogens would be able to run rampant around the body killing disease, and infected or dysfunctional cells would be able to pass on disease or raise the risk of cancer formation. The immune response is far more complex than this, with there being different types of B- and T-cells along with other lymphocytes (white blood cells), but this is beyond the scope of this article.

Vitamin A, when active in the body, is in the form of retinal. Retinal (specifically 11-cis-retinal) combines with a protein called opsin to make rhodopsin. When exposed to light, this rhodopsin undergoes a structural change, with the 11-cis-retinal part of the molecule converting to all-trans-retinal. This causes a change in the structure of the overall rhodopsin molecule, which in turn induces an electrical signal which passes along the optic nerve, onto the visual cortex of the brain. This improves colour vision, as well as allows better sight in low-light environments - which incidentally is where the idea that eating carrots (which are high in a form of vitamin A called beta-carotene) lets you see better in the dark comes from!

The RDA (Recommended Dietary Allowance) and UTL (Upper Tolerable Limit) of vitamin A

The RDA for vitamin A is 800 micrograms in the EU, 900 micrograms in the US & Canada, and 900 micrograms according to the Nordic Nutrition Recommendations. The Upper Tolerable Limit is 3000 micrograms.

The above RDAs are actually a slight oversimplification, as they refer to the RDAs and UTL for vitamin A when it is in the form of preformed retinol. Vitamin A actually comes in many different forms, and these all have different Retinol Activity Equivalents (RAEs). The RAEs of some of the different forms of vitamin A are as follows:

  • 2 micrograms of supplemented beta-carotene = 1 RAE

  • 12 micrograms of dietary beta-carotene = 1 RAE

  • 24 micrograms of dietary alpha-carotene = 1 RAE

  • 24 micrograms of dietary beta-cryptoxanthin = 1 RAE

So using the values of 900 micrograms RAE for the RDA and 3000 micrograms RAE for the UTL, you’d actually need to consume 10800 micrograms of dietary beta-carotene to meet your needs, and 36000 micrograms to hit the Upper Tolerable Limit. In practice, your body will stop converting beta carotene to the active retinol form once your needs are met, so it’s very unlikely you’ll experience toxicity symptoms from beta-carotene alone. 100 grams of raw carrot contains about 10000 micrograms of beta-carotene, so that alone can almost get you to the RDA (and cooking the carrot can actually increase the beta-carotene content).

Further to the above, lactating mothers need to make sure to consume more vitamin A than others to meet the nutrient needs of both them and their baby. The EU does not provide specific recommendations for this, but in the US and Canada, the Daily Value for lactating mothers is 1300 micrograms RAE. 

Signs of vitamin A deficiency

Extreme vitamin A deficiency can cause blindness, and increase the risk of death from various diseases like measles. It can also cause issues in foetal development, and can harm pregnant mothers. Less severe deficiencies can cause acne and other skin issues.

As mentioned previously, vitamin A helps form rhodopsin, which is involved in signal generation along the optic nerve. With an extreme vitamin A deficiency, insufficient rhodopsin can be generated for this, leading to blindness. In fact, vitamin A deficiency is the leading cause of preventable childhood blindness in the world according to the World Health Organisation. 

Due to vitamin A’s role in the immune system (via the generation of B- and T-cells), an inadequate intake can also lead to a compromised immune response. When a deficiency is extreme, this can increase the risk of death from various diseases, as the body is unable to fight them off due to the degree of immunocompromisation. 

Due to vitamin A’s involvement in healthy cell growth, a deficiency can lead to skin issues due to inflammation. This can lead to eczema or acne, with studies showing that some sufferers of these conditions can benefit from treatment with alitretinoin, which is otherwise known as 9-cis-retinoic acid, a form of vitamin A.

Signs of vitamin A toxicity

Vitamin A toxicity can be either acute or chronic, with chronic symptoms including vision issues, nausea, hair loss, headaches, dry skin and jaundice. Acute symptoms are rarer but more severe, and can even include death.

Vitamin A toxicity is rare when consuming foods rather than supplements, due to the quantities of intake required to experience problems, and because vitamin A in foods (aside from organ meats) is generally in a form like beta-carotene, not pre-formed retinol.

Chronic toxicity is caused by long-term ingestion of doses significantly over the Upper Tolerable Limit (around 5-10x the UTL). In addition to the symptoms above, this can cause itchy skin, poor appetite and confusion. In pregnant women, this can also impact fetal health.

Acute toxicity is far rarer, but also a lot more dangerous. Symptoms would typically appear within just hours or days, and can be very severe. Some estimates place the dosage for acute toxicity at around 7500 micrograms RAE per kilogram of body weight, but it’s best to just avoid huge doses to be safe, as effects include liver damage, increased cranial pressure and death. So steer clear of very high-dose supplements.

Finally, while beta-carotene and other carotenoids have not been associated with vitamin A toxicity in the same way, very high beta-carotene intake has been linked to a higher risk of lung cancer and heart disease in smokers.

What we use in our products

In our products, we include 900 micrograms of preformed retinol, and 1800 micrograms of beta-carotene. These amounts have been chosen to ensure nutrient needs are met, whilst not getting too close to the Upper Tolerable Limit.

The source of preformed retinol we use from v1.4 of GlycoGenesis and v1.3.3 of KetoGenesis is retinol acetate. Previously to these versions, we used retinyl palmitate. We made the change to entirely remove palm oil from our production line, because while we were assured the palm oil was responsibly sourced, this can be difficult to track reliably and the acetate form is just as bioavailable. The 900 microgram amount was chosen to fully meet all vitamin A RDAs on its own, for those who experience difficulties converting beta-carotene to retinol.

The source of beta-carotene we use from v1.4 of GlycoGenesis and v1.3.3 of KetoGenesis is a fermented form with a high ratio of cis-beta-carotene to trans-beta-carotene, due to the beneficial effects cis-beta-carotene can have in the body that all-trans-beta-carotene doesn’t seem to. Previously to these versions, we used a synthetic form of beta-carotene that was much higher in trans-beta-carotene. We include 1800 micrograms of beta-carotene: an amount that allows many of the benefits of cis-beta-carotene (such as inhibiting progression of atherosclerosis) and also achieves an optimal ratio of vitamin A to vitamin D - a topic we’ll discuss in greater detail in a future blog post on nutrient-nutrient interactions.