Vegan Vitamin A: How to get Enough on a Vegan Diet

Vitamin A is not generally known to be a potentially critical nutrient in vegan diets. However, it may be more difficult for some people to achieve an adequate status on a vegan diet than others.

Find out in this article why this is the case, and how you can achieve an adequate status on a plant-based diet.

Did you know that…

… there are about 50 carotinoids that belong to the provitamin A compounds?

Vitamin A: General Information

Vitamin A is a fat-soluble vitamin. This means that fats (and bile acids) are necessary for digestion. There are different vitamin A compounds that perform different functions in the body.

More than 95 % of the vitamin A in the body is stored in the liver, primarily as retinyl palmitate or stearate (retinyl esters), from where it is released into the blood as needed. On the one hand, this storage capacity means that the stores are sufficient for 1-2 years – provided they were well filled – but on the other hand, it also means that an oversupply is possible. This is because, unlike the water-soluble vitamins, excess vitamin A is not excreted through the kidneys and urine.

The body can get vitamin A in two ways:

• Via direct intake of preformed vitamin A (retinol in the form of retinyl esters) in foods of animal origin.
• Via endogenous (endogenous) conversion from carotenoids in plants. Products of animal origin also contain carotenoids. If animals are fed carotenoid-rich feed, the substances accumulate in the tissues (e.g. milk, cheese, butter, egg yolk).

Although vitamin A itself is not found in plant foods, it can be converted from carotenoids to vitamin A in the body. Carotenoids are therefore considered precursors for vitamin A and are referred to as pro-vitamins. Therefore, an adequate status is theoretically possible without the direct intake of vitamin A. However, there are other factors that influence the conversion and thus the extent to which vitamin A can assume its functions in the body (Westphal and Böhm, 2015).

Functions of Vitamin A

Vitamin A is involved in many important functions in the body. These include:

• involvement in the visual process
• support cell division
• participation in the growth process
• reproduction function
• support immune function
• involvement in embryonic development

(Heseker and Stahl, 2010).

You probably know beta-carotene as a carotenoid. But there are many others, such as alpha-carotene or beta-cryptoxanthin. However, not all carotenoids have provitamin A function. Lycopene and lutein, which you may know as the color-giving ingredient in tomatoes, are among them. However, this does not mean that they are “useless”. On the contrary, as phytochemicals, they perform important antioxidant functions in the body. This means that they prevent the formation of potentially harmful oxygen radicals (ROS) and thus prevent oxidative damage to DNA, for example. However, high-dose beta-carotene ingested via dietary supplements and under high oxygen partial pressure (for example in the lungs) as well as under strong oxidative stress were also observed to have pro-oxidant properties.

Beta-carotene performs the following functions, among others:

• stimulating effect on the immune system
• influence on cell differentiation, intracellular signaling pathways, apoptosis
• is used in the food industry as a colorant (E160a) (in butter, margarine, ice cream, desserts, as a vitamin additive) without maximum quantity restriction
• possible positive effects on disease risks (some cancers, type 2 diabetes mellitus, atherosclerosis; inflammatory diseases such as rheumatism and asthma)
• UV protection at 15-180 mg/d taken for at least 10 weeks (including lycopene) (not comparable with sunscreen!)

(Westphal and Böhm, 2015; transGen-Datenbank).

There is also evidence that vitamin A and beta-carotene may increase the absorption of iron by reducing the inhibitory effect due to phytates and tannins (Layrisse et al., 2000). This would be an interesting aspect for vegans because they often consume many of these inhibitors, which can have a negative effect on the bioavailability of iron or zinc, for example, and thus increase the risk of inadequate status.

However, this effect is not confirmed in all studies, and it is unclear whether it also applies to the intake of trivalent non-heme iron from plants. This is because in the studies, the subjects ate meals fortified with iron fumarate. This is divalent iron, which beta-carotene probably prevented from oxidizing to trivalent and thus became more available. The ratio of iron and beta-carotene in the meals also played a role, which is difficult to control in daily diet.

You see, an adequate supply of vitamin A is important. But how can you ensure your intake of vegan vitamin A is adequate?

Vitamin A on a Vegan Diet

When considering carotenoids as precursors to vitamin A, there are roughly two aspects to consider:

1. the bioavailability of the carotenoids
2. the conversion efficiency of carotenoids to the active vitamin A form

Bioavailability

Vitamin A in combination with fat has a bioavailability of 70 to 90 %, that of beta-carotene is between 5 % and 65 % (EFSA, 2019). On the one hand, this is relatively low, and on the other hand, it shows the second difficulty: the wide range of variation. How high the bioavailability of the carotenoids is depends, among other things, on

• the food matrix
• the method of preparation
• other components of the meal
• other carotenoids contained in the meal
• age
• state of health
• genetic factors

For example, in an in vitro study, beta-carotene from raw carrots had a bioavailability of only 3 %; when cooked, it was 27 %, and with fat, it was 39 % (Hedrén et al., 2002). You will get more tips later in the article.

Once the carotenoids have been absorbed in the intestine, the second aspect comes into play: this is where the provitamin A is converted to retinol. But how much vitamin A is produced from the carotenoids varies from person to person. Your genes play a crucial role. Read on for some interesting background information.

How Genetics Influences the Conversion of Beta-Carotene to Vitamin A

After absorption into the enterocytes of the intestinal mucosa (cells in the mucous membrane of the small intestine), provitamin A is converted into vitamin A by enzymes. According to current knowledge, two enzymes are responsible for this process: beta-carotene oxygenase 1 (BCMO1) and beta-carotene dioxygenase 2 (BCDO2). The former is the best known and probably the most important enzyme in this process.

But how active this enzyme is varies greatly between individuals. In studies, 27-45 % of people were classified as so-called ‘poor responders‘. They have a lower conversion rate. But what is the reason for that?

The gene that encodes (and thus activates) the enzyme BCMO1 can have different structures. In research, these variations in the nucleotides (which are the individual base pairs of the DNA) are referred to as “single nucleotide polymorphisms” (SNPs). These SNPs affect enzyme activities. SNPs located on the BCMO1 gene have been shown to reduce the conversion rate by 32-69 %, those located outside the gene by 48-59 %. They carry designations such as rs12934922, rs7501331, rs6420424, rs11645428, and rs6564851 (Leung et al., 2009; Lietz et al., 2012a; Lietz et al., 2012b).

Not only is the conversion of beta-carotene to vitamin A genetically variable, but SNPs are also known for the genes that affect the conversion of lutein and zeaxanthin. There are differences between ethnic groups in the prevalence of SNPs. In Europe, studies have shown that up to half of the population may be affected (Leung et al., 2009). Accordingly, those who are carriers of one or more polymorphisms can form only little vitamin A from carotenoids. In the case of a vegan diet, that means when no preformed vitamin A is consumed at all, this could make an adequate status very difficult.

Due to the many functions that vitamin A performs in the body, a deficiency can have negative consequences.

Vitamin A Deficiency

A temporary undersupply does not immediately lead to deficiency symptoms because the liver stores last for a while. The first symptoms can only be expected after about six months. Vitamin A deficiency symptoms include:

• impaired vision
• night blindness
• blindness
• skin and mucous membrane changes
• growth arrest
• impairment of the sense of smell and taste
• disruption of the reproductive function
• digestive and absorption disorders
• increased tendency to infections

But does that mean you should supplement to be on the safe side? This is only recommended to a limited extent. As with all fat-soluble nutrients, hypervitaminosis (oversupply) is possible and can have dangerous consequences.

Oversupply of Vitamin A

The Tolerable Upper Intake Level (UL) for vitamin A is 3 mg RAE per day for adults, and postmenopausal women are recommended to consume no more than 1.5 µg RAE daily. This means that if this amount is consumed every day for a lifetime, adverse health effects are unlikely (SCF and NDA, 2018; EFSA, 2006). Hypervitaminosis from dietary vitamin A is very unlikely and may occur at most with regularly high liver consumption. If pregnant and in the first trimester, it is recommended to avoid consumption of liver and vitamin A supplements to be on the safe side, as malformations in the embryo could occur (Biesalski et al., 2020).

An acute intake that is too high can lead to

• nausea
• vomiting
• headache
• standing disorders
• itching

The consequences of chronic overconsumption are non-specific, such as

• scaly skin
• hair loss
• fatigue
• bone, joint and muscle pain.
• swelling of the spleen and liver and cirrhosis of the liver after a long period of time

(Heseker and Stahl, 2010).

By the way: An oversupply of vitamin A in a vegan diet with beta-carotene is not possible because in the body the conversion is down-regulated when sufficient vitamin A is available. You may have noticed a yellowing of the skin if you have eaten a lot of carrots, pumpkin and sweet potato. This may look a bit strange at first, but it is no reason to worry. This phenomenon, which is technically called “carotenoderma“, is not dangerous to health. It only reflects high intake (Biesalski et al., 2017).

However, a high intake of beta-carotene via dietary supplements is not recommended. This is because there is evidence that the risk of lung cancer is increased, especially in heavy smokers. EFSA considers the intake of up to 15 mg of beta-carotene from dietary supplements and food additives to be safe (EFSA, 2012). Observational studies also show a possible association between high vitamin A intake (but not beta-carotene) and increased risk of hip fractures (Knapik and Hoedebecke, 2021; Charkos et al., 2020).

So you see, neither under- nor oversupply is good. But how do you know whether your intake of vegan vitamin A is sufficient?

Checking the Nutritional Status

Unfortunately, it is not so easy to determine the nutritional status of vitamin A. This is because the blood level of retinol is not well suited for this purpose due to the body’s own regulatory mechanisms. If levels are low, the deficiency is already severe (Biesalski et al., 2017). In addition, plasma concentrations may be influenced by other factors, such as infections, and elevated retinol concentrations do not necessarily indicate an oversupply, but may also indicate renal dysfunction (Heseker and Stahl, 2010).

A liver biopsy is indeed the most reliable method to check the status. But this is not practical. A functional and relatively reliable method is the so-called “relative dose-response (RDR) test“. In this test, retinyl palmitate is administered orally and the change in serum retinol is then observed. Changes of 20  % or more are considered to be indicative of a deficiency. However, this method is also very complex. The modified RDR, in which 3,4-didehydroretinyl acetate is administered, and the retinol binding protein (RBP) RDR test, as well as other methods, have been proposed as possible simpler alternatives (Tanumihardjo, 2012; Fujita et al., 2009).

In contrast, it is relatively easy to check the nutritional status of beta-carotene. This is because plasma levels are a reliable parameter. However, there are no defined levels at which a deficiency occurs; the best preventive effects probably occur at 0.5 µmol/l, and a deficiency could be present at less than 0.3 µmol/l. High fasting concentrations could indicate reduced conversion (Biesalski et al., 2017).

Even if it is not possible for you to measure your vitamin A status directly, you can get an idea of whether you are consuming enough carotenoids to (theoretically) provide an adequate vitamin A status.

Needs and Intake Recommendations

First, you can check how many carotenoids you consume in your diet and compare this amount with the current reference values for nutrient intake. To do this, you can use tablesof food nutrients, software programs or our Nutrient Database, in which the carotenoid contents are specified.

The D-A-CH reference values (for the German speaking countries) for vitamin A are “recommended intakes”. For adults, it is 850 µg RAE for men and 700 µg RAE for women. Pregnant and breastfeeding women have a higher requirement (800 and 1300 µg RAE, respectively) (DGE, 2020b).

What does the “RAE” stand for? It is the abbreviation for “retinol activity equivalent” and the use takes into account the respective biological activities of the different vitamin A forms. This is to account for the different pro-vitamin A activity and usability of the carotenoids. Interactions with other food ingredients and availability from food items are also considered. Accordingly, the following applies:

1 µg RAE = 1 µg retinol (the active form)

1 µg RAE = 12 µg beta-carotin

1 µg RAE = 24 µg other provitamin A carotenoids.

You can see that, compared to preformed vitamin A, twelve times as much beta-carotene must be ingested to achieve the same efficacy. However, these conversion rates and derived recommendations apply to a mixed diet. Whether higher amounts are necessary in a vegan diet is unclear. For those with genetically limited conversion efficiency these average recommendations may not be enough. It is also important to ensure an adequate amount of fat in the diet and a good digestion of fat.

So it might be more difficult to ensure a sufficient intake of vitamin A as a vegan, especially with a specific genetic disposition. But how do you know whether you can convert only little of the beta-carotene to vitamin A? Especially with a vegan diet, this would be important information.

For this purpose, one can use genetic testing. But caution is advised here: Only a few commercially offered “genetic tests” provide reliable information on this. This is possible, for example, through “genotyping tests”, which provide information about existing gene variants on the basis of saliva samples. If you want to do such a test, inform yourself extensively about the test methods and whether relevant genetic variations are examined at all. Regardless of this, you would do well to keep an eye on vitamin A in your vegan diet.

Tips for the Intake of Vitamin A on a Vegan Diet

You cannot (currently) change your genetics. But you can improve your vitamin A intake on a vegan diet in four ways:

1. Choose foods high in carotenoids.
2. Use preparation methods that increase bioavailability.
3. Reduce the bioavailability inhibiting factors.
4. Supplement vitamin A.

Vegan Vitamin A Food

The preformed vitamin A is mainly found in foods of animal origin such as butter, liver, egg and cheese. Sample RAE contents can be found in Table 1.

Table 1: Vitamin A From Food of Animal Origin (BLS)

In a vegan diet, you should make sure to include food items with high RAE content. An overview of good vegan sources can be found in Table 2.

Tabelle 2: Vegan Food Items for Vitamin A Intake (BLS)

The quantities and compositions of carotenoids depend, among other things, on the growing conditions, the degree of ripeness at harvest, processing and storage. Since the bioavailability is also very strongly influenced by the preparation, the orientation on such tables is only of limited help. You will learn more about this later (Westphal and Böhm, 2015; Biesalski et al., 2017).

You can influence the levels in your food:

• Chop and heat just before eating.
• Do not heat them too much and for a long time (< 100 °C).
• Be sure to store them in a cool place away from light.
• Do not store them for too long.
• Juicing fruit can release organic acids, which can accelerate decomposition.

(Westphal and Böhm, 2015).

Integrate carotenoid-rich foods into your diet on a regular basis. This way, you will benefit from the improved vitamin A supply and the effects of the phytochemicals. The DGE has listed two examples of vegan foods with which you can meet your RAE requirements within one day (DGE, 2020a):

Table 3: Covering Vitamin A Requirements on a Vegan Diet (Example 1)

Table 4: Covering Vitamin A Requirements on a Vegan Diet (Example 2)

That doesn’t actually look difficult, does it?

But: The reduced conversion efficiency of many people is probably not sufficiently taken into account. Therefore, it is not clear whether these amounts are sufficient for everyone who eats a vegan diet. To reduce the risk of vitamin A deficiency, you can improve the bioavailability of the ingested carotenoids.

Increasing Bioavailability

The bioavailability of carotenoids in food depends, among other things, on the food matrix, i.e. other food components, other carotenoids in the meal, fat content and type, and the age of the person taking in it.

You can improve the absorption of carotenoids in the gastrointestinal tract by

• Combining beta-carotene-containing foods with fats: an improvement is probably achieved at 2.4 to 5.0 g (DGE, 2020a). This may increase BCMO1 activity and result in the secretion of bile salts, which are necessary for emulsification and thus absorption. Probably, in the context of a balanced diet, the intake does not necessarily have to occur simultaneously; it seems to be sufficient if it is a few hours apart, for example at the next meal (Ribaya-Mercado, 2002).
• Breaking down the food (cut it into small pieces, puree it, chew it intensively). This breaks down the cellular matrix, loosens the bond to protein and releases the carotene from the intracellular organelles (Westphal and Böhm, 2015).
• Gently cooking the food. This also breaks down the cellular matrix. However, you should avoid overheating, as this will result in preparation losses (Westphal and Böhm, 2015).

These are the best-known and best-proven ways to improve the bioavailability of carotenoids. There is also evidence from in vitro studies (in the laboratory on cells) that calcium could increase absorption by up to 100 %. However, opposite effects have also been observed in humans. The amounts of calcium that are probably required can usually only be achieved via supplements; calcium carbonate was used here. Probably, the effect depends, among other things, on the calcium type and amount, the type of carotenoids, and the food matrix.

The same applies to iron and zinc: In studies, 20 mg of iron fumarate or zinc sulfate improved the vitamin A status. However, also in this respect, no clear findings can currently be derived for practical application. There are also studies in which inhibitory effects were observed with these nutrients (Corte-Real and Bohn, 2018).

Reducing Factors That Inhibit Absorption

The absorption of beta-carotenoids could be reduced by (high amounts of) iron, zinc, calcium and magnesium. This effect was shown in different studies. However, the amounts used are generally not consumed in everyday life; for calcium and magnesium, they could be achieved through high-dose supplementation. You could separate the intake of these supplements from a carotenoid-containing meal to be on the safe side. One possible reason for their inhibitory effect is that these divalent metal ions can bind free fatty acids and bile salts, which could inhibit the absorption of beta-carotene (Corte-Real and Bohn, 2018).

Furthermore, dietary fiber reduces the intake, which is often consumed in large quantities in a vegan diet. Since the carotenoid-containing foods are usually rich in fiber at the same time, this cannot be avoided on the one hand and balances itself out on the other. However, you can be careful not to take in too much fiber and especially limit the amount of isolated fiber (guar gum, locust bean gum, xanthan gum, etc.). This not only has a positive effect on the absorption of beta-carotene, but also on the availability of other nutrients (Westphal and Böhm, 2015).

Practical Implementation

Here are a few exemplary meals, with which you can improve your intake of vitamin A on a vegan diet:

• peppers stuffed with amaranth in tomato sauce from the oven
• pumpkin-sweet potato soup
• pumpkin curry
• veggie-quiche
• sweet potato-mango soup

Supplementing Vegan Vitamin A

Another way to reduce the risk of insufficient vitamin A intake in vegan diets is to consume preformed vegan vitamin A via dietary supplements. This bypasses the conversion step and thus potential gene polymorphisms do not play a role. Products with retinyl palmitate or retinyl acetate can be used.

Since the intake of preformed vitamin A is very close to the UL in high consumers according to the National Consumption Study II, foods may not be fortified with vitamin A in Germany (exception: margarine or mixed fat products) and the Federal Institute for Risk Assessment (BfR) recommends a daily intake (including a safety factor) of 0.2 mg per day. Accordingly, this maximum dose is intended to prevent oversupply in consumers with the highest intake – it is less relevant in vegan diets (BfR, 2021).

The Linus Pauling Institute at Oregon State University recommends a dose of no more than 750 μg (2500 IU) of vitamin A for daily long-term supplementation (Linus Pauling Institute, 2021). Thus, this amount is roughly equivalent to the DGE’s intake recommendation for vitamin A. Since vegans do not ingest preformed vitamin A in their diet and this dosage is far from UL, it can be considered adequate for vegans. However, you only know whether it is adequate by checking your status.

When choosing a supplement, make sure it is a synthetically produced form of vitamin A, made without ingredients of animal origin. A supplement with added fat might somewhat aid in absorption if the meal does not contain enough fat.

Conclusion: Vegan Vitamin A

Vitamin A is usually not counted among the potentially critical nutrients in vegan diets. This is because even though it is not itself found in plant foods, conversion from carotenoids is possible.

But: On the one hand, the carotenoids have a low bioavailability, on the other hand, the conversion rate is very variable and, depending on genetics, it can be severely limited. This can make it difficult to obtain an adequate status of vitamin A from carotenoid intake alone. Because of the limited ability to determine deficiencies or find out if you have a genetic predisposition to reduced conversion, low-dose supplements of preformed vegan vitamin A can be considered. However, it is always best to consult with your doctor before taking these supplements, as interactions with medications are possible. In addition, high-dose supplements should not be taken as a preventive measure to avoid an overdose with harmful consequences.

However, the findings on reduced conversion and the inferred assumption that some vegans are at high risk for insufficient vitamin A intake are not based on clearly established knowledge. The relevance of genetic polymorphisms to everyday (vegan) diets is not clear. Whether vegans are at high risk for adverse health effects due to inadequate vitamin A intake is currently not clear. However, it is an exciting topic to keep an eye on as a vegan.

Our recommendation: Keep your beta-carotene intake high through food and pay attention to measures to increase bioavailability. A moderate-dose vegan vitamin A supplement, for example in a multivitamin, can be used.

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Image Sources

Image Sources

• Title Image – Vitamin A: © Yulia Furman - stock.adobe.com

Medical Disclaimer and Other Notes

Medical Disclaimer

Like any science, medicine and related disciplines are subject to constant development. Research and clinical experience expand our knowledge, especially with regard to treatment and therapy. Insofar as a recommendation, dosage, application, etc. is mentioned in the information provided, you may trust that we have taken great care to ensure that this information corresponds to the state of knowledge at the time of completion of the work. However, no guarantee or liability can be assumed for such information. You are required to check them carefully yourself and act on your own responsibility. Furthermore, our recommendations and advice are in no way intended to replace medical advice, diagnosis or treatment in the case of an existing illness - it is not a therapy. You should therefore never use the information we provide as your sole source for making health-related decisions. In case of complaints, medical advice should be sought in any case.