Amount of Evidence: Low Potential Benefits: Reasonable Safety: Reasonable
TABLE OF CONTENTS
What is vitamin A?
Vitamin A is a fat-soluble vitamin with many functions in the body. Its different forms are often called “retinoids.” They include retinol, retinal, retinoic acid, and retinyl ester. While vitamin A supplements can be very useful for fixing a deficiency, they can easily cause more harm than good. In this article, we will look at vitamin A’s main benefits, potential side effects, and how to use it the right way.
Potential benefits
It is important to note that all of the potential benefits mentioned below are dose-dependent. In general, the higher the dose you take, the more pronounced the effects will be. However, they do reach a plateau at a certain point. We will discuss the best dosing protocol later in this article.
Major benefits
Correcting a vitamin A deficiency – A deficiency in vitamin A can have a terrible impact on health and overall quality of life. Fortunately, a severe deficiency is not as common as a deficiency of many other nutrients. A moderate deficiency is way more common and can lead to many problems you will learn about later in the article. If you experience some of the symptoms of deficiency or you know your vitamin A levels are too low, fixing a deficiency is the main benefit of vitamin A supplements.
Minor benefits
Reduced wrinkles – Topical use of retinol has been shown to reduce wrinkles in older people.
Reduced intensity of measles – The supplement has been shown to reduce the risk of measles complications or death in children with measles and vitamin A deficiency.
Unproven benefits
The effect of vitamin A on these parameters has either not been sufficiently researched or the science shows little to no efficacy in these areas.
Skin cancer – While the vitamin can help reduce wrinkles from sun damage, it does not reduce the risk or the progression of skin cancer.
Head and neck cancer – Taking vitamin A by mouth does not reduce the risk of developing new tumors or improve survival in people with head and neck cancer.
Blood flow – No significant change has ever been noted.
Blood pressure – There isn’t any strong evidence to support vitamin A supplements help with blood pressure to a notable degree.
DNA protection – Vitamin A has never been shown by human studies to protect DNA from oxidative damage.
Triglycerides – No significant influence has ever been noted.
Cholesterol – Vitamin A does not directly influence HDL or LDL cholesterol levels.
VO2 max – The supplement does not appear to directly improve your VO2 max.
Risk of stroke – Relative to placebo, vitamin A supplements have never been shown to reduce the risk of stroke.
Serum T3 and T4 – There is no significant interaction between vitamin A supplements and serum T3 and T4.
Well-being – Vitamin A supplements do not reduce rates of depression. They also don’t appear to increase subjective well-being in any way, assuming you are not deficient.
Weight – The supplement does not lead to weight loss or weight gain.
Strength – Vitamin A supplements do not help you gain strength or muscle mass faster.
Asthma – The supplement has never been shown to notably help with asthma.
Power output – Vitamin A does not influence power output during cardio or resistance training. It does not impact endurance either.
Kidney function – Biomarkers of kidney function are not significantly altered with supplementation of vitamin A relative to placebo.
Sleep quality – The supplement does not appear to increase sleep quality. It also does not affect sleep duration.
Stress and anxiety – Vitamin A supplements do not directly impact cortisol levels. They may indirectly lower stress and anxiety levels if you are deficient in the nutrient.
Metabolic rate – The supplement does not speed up your metabolism, nor does it slow it down.
Possible side effects
These side effects are dose-dependent and the risk for them increases (most often linearly but sometimes exponentially) as you increase the dose. Some of the side effects are only relevant to very high doses.
Vitamin A toxicity – Mild toxicity can cause liver damage, fatigue, hair loss, nausea, vomiting, dry skin, cracked lips, and headaches. Severe toxicity could lead to death. However, that would only happen if you took extremely high doses of vitamin A or ate certain types of liver in huge quantities. The side effect doesn’t really apply to carotenoids since they are very unlikely to cause toxicity in most people.
Increased risk for cancer – Retinyl palmitate has been associated with DNA damage and an increased risk for skin cancer and other types of cancer in animals.
Imbalance in fat-soluble vitamins – Vitamins A, D, E, and K get broken down in the body by the same mechanism. Since they share the same breakdown pathways, consuming lots of one vitamin may increase the breakdown of the others. So if you take too much vitamin A, your body may turn on this pathway and break down more of the other vitamins as well. Put simply, megadosing one of those fat-soluble vitamins is not the best idea unless you also increase your intake of the other ones.
Diarrhea – This side effect is not dangerous (assuming the diarrhea doesn’t lead to severe dehydration) and typically only occurs if you take very high doses at once.
Nausea – Just like diarrhea, this side effect is not dangerous.
Birth defects – Too much vitamin A can cause birth defects, especially in the first 8 weeks of pregnancy.
Who should not take vitamin A?
You should probably avoid taking the vitamin if you:
already get a lot of vitamin A from food
do not experience symptoms of deficiency
are deficient in other fat-soluble vitamins (D, E, and K)
are pregnant (too much vitamin A can cause birth defects, especially in the first 8 weeks of pregnancy)
suffer from liver disease (too much vitamin A can make the disease worse)
Who will benefit the most?
You should consider taking the vitamin if you:
experience symptoms of vitamin A deficiency or you know you are deficient from blood tests
don’t get enough vitamin A from food
are a vegan or vegetarian
are on a low-fat diet
have genetics that make you poor at converting carotenoids to retinol (around 50% of us have an impaired ability to convert carotenoids to retinol by 50-75%)
supplement with high doses of other fat-soluble vitamins (vitamin D, E, and K)
suffer from hypothyroidism, zinc deficiency, or iron deficiency (since these can hurt the conversion of beta-carotene to retinol)
Forms of vitamin A
The forms of vitamin A include:
Beta-carotene – Carotenoids are mostly plant-based forms of vitamin A named after carrots. There are over 700 carotenoids but beta-carotene is the most popular one. While you do not need beta-carotene to survive and it doesn’t do much on its own, it can convert to retinol, the active form of vitamin A.
Retinol – This is the active form of vitamin A, found primarily in animal organs. Retinol is named after the retina which is a part of the eye where most of the vitamin A is found.
Lutein– While lutein is a carotenoid and therefore a part of vitamin A, it doesn’t act like beta-carotene or retinol in the body. Lutein’s primary function is that it can protect us from going blind when we get old.
Zeaxanthin– This carotenoid is very similar to lutein.
Astaxanthin– Astaxanthin has a similar structure to that of lutein or zeaxanthin but appears to be more beneficial as a dietary supplement.
Beta-cryptoxanthin – This carotenoid mainly acts as an antioxidant.
Lycopene– Just like lutein and zeaxanthin, lycopene is a carotenoid but doesn’t act like vitamin A. This form is almost exclusively found in tomatoes and it may have some benefits that retinol doesn’t, such as reducing the risk for prostate cancer.
Alpha-carotene – Just like beta-carotene, alpha-carotene can act as provitamin A, meaning it can convert to retinol.
Retinyl palmitate – Retinyl palmitate is a synthetic retinyl ester. In the body, it is harder to utilize this form than retinol. Also, this form has been associated with an increased risk for skin cancer and other issues and should therefore be avoided.
Retinyl acetate – Retinyl acetate is an acetate ester of retinol. While this form appears to be safer than retinyl palmitate, it can still lead to many of the side effects associated with it.
This article is specifically about retinol and carotenoids that convert to it. The benefits and side effects above do not necessarily apply to lutein, zeaxanthin, astaxanthin, beta-cryptoxanthin, and lycopene.
If you wish to supplement with vitamin A to fix a deficiency, beta-carotene is the best option.
Retinyl palmitate and acetate have a much worse risk-to-benefit ratio compared to beta-carotene and should therefore be avoided.
Signs of vitamin A deficiency
The most common symptoms of deficiency include:
dry eyes
trouble seeing at night
getting common colds regularly
difficulty falling asleep or waking up
fatigue throughout the day
crusty skin
kidney stones
bumps on the skin that look like goosebumps or acne but they never go away
asthma
allergies
Keep in mind that these signs are just indications of deficiency. If you experience some of them, it doesn’t necessarily mean that you need more vitamin A. On the other hand, some people may have a deficiency even though they are completely asymptomatic.
With that said, if you experience many or most of these symptoms, there is a high chance you are not getting enough vitamin A. The more of these symptoms you experience and the more severe they are, the more likely you are deficient.
How much vitamin A should you take?
The RDA (recommended daily allowance) is measured using RAE (retinol activity equivalents). This metric is an estimate of how much retinol your body can produce and utilize from the sources of vitamin A you are eating.
While RAE is somewhat simplified in that it doesn’t take into account that different people have different conversion rates of carotenoids to retinol, this metric is still highly useful and accurate.
The RDA is 900 mcg of RAE daily for men and 700 mcg for women. This is a great recommendation to follow for most people.
Even if you have an impaired conversion of carotenoids to retinol, the RDA should be enough to avoid deficiency because it accounts for this.
Breast-feeding significantly increases your needs for vitamin A, to around 1300 mcg of RAE per day.
Because this is a relatively easy target to hit with food alone, taking extra vitamin A from supplements is usually not necessary and could easily cause more harm than good.
However, if you know you are not getting enough vitamin A from food, taking around 1500 IU (or around 500 mcg worth of RAE) per day is probably a good idea. The safest form to use is beta-carotene.
Unless you are trying to fix a severe deficiency, taking more should not be necessary and it would increase the potential side effects.
Food sources of vitamin A
The richest food sources of carotenoids are red, orange, yellow, and green vegetables. Carotenoids like beta-carotene have the potential to color the vegetable either orange, yellow, or red.
The reason why green vegetables are also rich in carotenoids is that carotenoids help keep the chlorophyll in the plant. If you’ve ever noticed leaves turning red, yellow, and orange during autumn, it is because they are losing chlorophyll so the carotenoids are getting revealed.
While this is a very simplified recommendation, 3-5 cups of vegetables rich in beta-carotene should provide more than enough vitamin A for the vast majority of people.
Cooking vegetables rich in carotenoids significantly increases their bioavailability.
As for retinol (the animal-based form), liver is the richest source of it. This is because all mammals store vitamin A in the liver. Other types of meat are very low in retinol. The only decent animal sources of retinol other than liver are eggs and dairy.
The easiest way to find out how much vitamin A you are getting in your diet is with Cronometer.com – the app is free and allows you to track all vitamins, minerals, and more.
Best time to take vitamin A
Since this vitamin is fat-soluble, you need to take it with a source of fat if you wish to maximize the absorption.
More fat will lead to better absorption than less fat in the case of vitamin A so you want to take the vitamin or eat the richest sources of it with the meal highest in fat.
Whether you take the supplement in the morning or the evening doesn’t really matter.
You also do not have to take the vitamin every day. There is not a big difference (if any) between taking 1000 IU every day and taking 3500 IU twice a week.
Interactions with other supplements
Vitamin D Vitamins A, D, E, and K get broken down in the body by the same mechanism. Since they share the same breakdown pathways, consuming lots of one of these fat-soluble vitamins may increase the breakdown of the others. So if you take too much vitamin A, your body may turn on this pathway and break down more of the other vitamins as well. Put simply, megadosing one of those fat-soluble vitamins is not the best idea unless you also increase your intake of the other ones.
Vitamin E The same said about vitamin D also applies to vitamin E.
Vitamin K The same said about vitamin D and E also applies to vitamin K.
Alcohol Alcohol can increase the potential of retinol supplements to cause liver damage.
Where to buy vitamin A
Amazon seems to be the best option for ordering vitamin A supplements in most countries. They offer some very affordable products that are backed by many positive reviews. Also, you can choose from a wide range of brands there without having to spend time searching through other markets on the internet.
One thing you should pay attention to is that some brands display the dosage per serving and not per pill or capsule. Therefore, you may accidentally buy something less potent than you intended. Do not fall for this marketing trick.
FAQ
The supplement can be taken daily and does not need to be cycled.
Yes. The vitamin doesn’t impact your sleep in any negative way in the short term.
Vitamin A supplements rarely go bad but they can lose potency over time.
Keep your vitamin A supplements in a cold, dark, and dry place and they will remain just as potent for many years.
It doesn’t directly reduce acne, unfortunately.
Definitely. While severe vitamin A toxicity is rare, too much vitamin A in the system can cause multiple problems. Mild toxicity can lead to liver damage, fatigue, hair loss, nausea, vomiting, dry skin, cracked lips, and headaches
Too much vitamin A can also cause an imbalance in fat-soluble vitamin ratios. Vitamins A, D, E, and K get broken down in the body by the same mechanism. Since they share the same breakdown pathways, consuming lots of one vitamin may increase the breakdown of the others. So if you take too much vitamin A, for example, your body may turn on this pathway and break down more of the other vitamins as well. Put simply, megadosing one of those fat-soluble vitamins is not the best idea unless you also increase your intake of the other ones.
Beta-carotene is the safest option that can provide just as much if not more benefits than the other forms.
Retinyl palmitate and retinyl acetate have a much worse risk-to-benefit ratio compared to beta-carotene and should therefore be avoided.
The most common reason people become deficient is that they don’t get enough of the vitamin from their diet.
However, genetics can also lead to a deficiency. Around 50% of us have an impaired ability to convert carotenoids to retinol by 50-75%. Hypothyroidism and iron or zinc deficiency can also hurt the conversion.
You probably need more of the vitamin if you: – experience signs of deficiency – don’t get enough vitamin A from food – are a vegan or vegetarian – are on a low-fat diet – have genetics that make you poor at converting carotenoids to retinol (around 50% of us have an impaired ability to convert carotenoids to retinol by 50-75%) – supplement with high doses of other fat-soluble vitamins (vitamin D, E, and K) – suffer from hypothyroidism, zinc deficiency, or iron deficiency (since these can hurt the conversion of beta-carotene to retinol)
Beta-carotene supplements are vegan-friendly. Retinyl palmitate and retinyl acetate supplements may and may not be vegan-friendly, depending on the brand and their sourcing. Fortunately, beta-carotene appears to be the safest form anyway and it can be just as effective if not more effective as the other forms.
Since these vitamins are fat-soluble, you need to consume dietary fat with them to absorb them properly. Taking these vitamins or consuming them from low-fat food sources without adding extra dietary fat can make some of them up to 10 times less bioavailable. Fortunately, as little as 20 grams of fat should be enough to absorb these vitamins well.
References
Most of the information provided in this guide is based on scientific research that can be found and verified in the PubMed medical library. We excluded from consideration studies that are either confounded or have a high conflict of interest.
Anecdotal evidence (from reports on Reddit, YouTube, and other sources) is also taken into account unless it contradicts scientific research.
