Vitamin A got its name because it was the first vitamin to be discovered.  

In the 1880’s an unknown substance, with a growth supporting “accessory factor” was identified as essential to human nutrition. This became known as fat-soluble A until it was finally isolated, crystallised and renamed vitamin A in 1937.

Confusion over carrots

The forms of vitamin A the body requires are derived from retinol. Retinol is preformed vitamin A found in animal foods.

This differs from the vitamin A precursors, (beta carotene and the other carotenoids) abundant in the highly coloured fruits and vegetables. To be usable, these carotenoids must be converted into retinol in our digestive system. The rate of this is conversion is about 12-to-1 in a healthy person with good gut function.

Despite carrots legendary status for providing vitamin A, you would need to eat 48 carrots each day to prevent vitamin A deficiency.  

Conversion and absorption issues

Chronic disease, digestive inflammation, poor lipid metabolism, alcohol use and some medications make it difficult to convert carotenoids into retinol. Our genes affect this process, with 45% of the population being “non-converters”. This significantly reduces the ability to make retinol from plant foods as well as limiting the levels of vitamin A that can circulate in the bloodstream.

When it comes to thyroid function, vitamin A is a double-edged sword. We need thyroid hormone to turn carotenoids into retinol the digestive tract and we need retinol to create thyroid hormone. Retinol is important for T3 to activate the genes that control our metabolism.Did your GP check your vitamin A levels when testing your thyroid function? This is important; particularly if you’re taking thyroid medication and continue to experience the symptoms of low thyroid.

Because it’s fat-soluble, Vitamin A is absorbed best when it’s eaten with some fat. This means we need a healthy gallbladder, to produce bile to emulsify the fat, so it can be transported in the blood stream. For people without a gallbladder or with gallbladder dysfunction the risk of vitamin A deficiency increases significantly.

What happens when we don’t get enough

Vitamin A has wide ranging benefits for our health, some we don’t hear much about.

It a powerful antioxidant that helps to scavenge free radicals and fight inflammation.

Other biological processes dependent on vitamin A include healthy skin and the proper function of our lungs, heart, and kidneys. It plays vital role in the regulation of gut health including the microbiome, digestive inflammation, and leaky gut.

Vitamin A is well known for its role in vision – dry eyes, night blindness, cataracts, and macular degeneration. It’s helps to make the hormones testosterone and oestrogen, important for fertility and reproduction. Without enough vitamin A, boys won’t go through puberty.  It helps protect us from age-related loss of muscle strength, physical and cognitive disability. It’s vital for cell growth and differentiation, immune function, and reduces the risk of chronic diseases such as type-2 diabetes, heart disease and cancers.


An important and underrated role of vitamin A is in the production of red blood cells and haemoglobin. Suboptimal levels of vitamin A are seldom considered in the assessment of anaemia. Retinol regulates iron metabolism and many other important metabolic pathways.

Retinol in conjunction with copper plays a vital role in the iron recycling system. See here

Playing nicely together

It’s impossible to separate out the individual roles of all the essential nutrients. They are all needed in their bioavailable forms and the right combinations with each other to ensure a healthy well-functioning body.

Vitamin A and D balance is an example of these interactions. These work harmoniously together to ensure good health, but when they become out of balance, they compete for the same receptors and can block the absorption of each other. Remember vitamin A plays alongside magnesium, copper, zinc, and iron. Although supplementing individual nutrients such as zinc and vitamin D has become popular (particularly during Covid), I urge you to check that you need them and to avoid overuse.

Testing vitamin A status

Blood testing (serum or plasma) is the most common, however like all nutrition testing, accuracy and interpretation can pose a challenge.  Although considered reasonably accurate in determining deficiency, an isolated serum vitamin A test may not tell us much about your status and what’s going on. Comprehensive vitamin and mineral testing is more useful as it provides insights into the bigger picture, rather than basing information off high and low values of single tests.

There are many reasons why nutrients test high or low that may not be related to your intake. Despite the challenges with testing, I believe these can help when getting to the root cause of health problems. Results can provide good motivation to make nutritional and lifestyle changes and may be useful when assessing the efficacy of supplements in restoring nutrient balance.

Vitamin A in foods

Like many essential nutrients, the preformed vitamin A (retinol) is found exclusively in animal foods. The best sources are liver, eggs, seafood/fish, butter and other dairy products.

For those who don’t eat liver or can’t consume dairy, organ supplements and cod-liver-oil provide good food-based options. Remember, if you’re selecting cod-liver-oil avoid those with synthetic vitamin D, zinc and other additives.

Vegans and vegetarians may struggle to get enough vitamin A in their diets. Many fruits and vegetables are high in carotenoids including sweet potato, squash, carrots, kale, mangos, nectarines and apricots. Unfortunately, it can be difficult to convert these into retinol, particularly when hypothyroid and gut inflammation is present. The high fibre along with high phytate and oxalate levels found in many fruits and vegetables reduced the conversion factor. Another important consideration requirement of fat to enhance absorption. This is often low in plant-based diets.

Eating real food

While I love understanding the biochemical pathways of the individual nutrients involved in our health, at the end of the day we evolved to get these from the foods our ancestors ate, without needing biochemistry degrees. An ancestral real food diet is the first place to start when improving health. In our modern food environment, this can be challenging for many reasons and there are times when supplementation may be necessary. I encourage you to use food-based supplements first and give them time to work. It can take years for nutrient deficiencies to show up as symptoms and these can take a long time to resolve.

While a nutrient dense diet is a prerequisite for good health, eliminating the harmful foods is equally important. Start with the vegetable oils, PUFA’s. These are extremely damaging. Eliminate those junk processed foods such as crips, cakes and cookies. I consider the highly processed breakfast cereals and other wheat-based products in this category. Check the labels not only for the sugar content but all the synthetic vitamins that are added in the name of good health.

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