These days, during the seasonal transitions, it seems like everyone around is catching a cold or getting infected – sometimes it’s the flu, sometimes a seasonal virus, and occasionally even COVID. Coughing, fever, and sneezing have almost become part of the routine of this time of year.
Contrary to what many believe – that vitamin C is the most important vitamin for the immune system – when it comes to viral infections, especially those typical of seasonal changes, it is actually vitamin A that is the most important. It directly affects the immune system from the very first stage, in the respiratory system, and keeps the mucous membranes functioning as a barrier that prevents viruses from penetrating inside.
Adequate levels of vitamin A are particularly important for protecting the mucous membranes of the respiratory system – the first place where viruses try to enter the body.
Many studies show the direct link between vitamin A levels and the risk of infection: A comprehensive review published in The Lancet found that vitamin A supplements in populations where deficiency exists reduced infections in children by about 24%.
Another study from the Journal of Clinical Medicine showed that a deficiency in vitamin A significantly increases the sensitivity of the respiratory tract to viral infections.
In other words, vitamin A is truly an essential component of the body’s ability to block viruses right at the entry point – in the mucous membranes of the nose, throat, and lungs.
How much is needed per day?
The official recommendations (RDA) are about 700 micrograms per day for women and about 900 micrograms per day for men. Pregnant women need slightly more, and children, of course, less.
There are animal-based sources – where the vitamin appears as retinol (the active form), and plant-based sources – where it appears as beta-carotene and other derivatives that the body can convert as needed.
In animal-based foods –
It appears as retinol, the active form that the body can use immediately. Therefore, liver, egg yolks, full-fat cheeses, and butter provide especially available vitamin A.
In plant-based foods –
The vitamin appears as carotenoids (mainly beta-carotene, but also lutein and zeaxanthin), which the body must convert into retinol. This conversion process is not always equally efficient and depends on personal factors such as genetics, health condition, and fat intake. Therefore, not everyone who eats a lot of carrots or sweet potatoes will necessarily reach the same vitamin A levels as someone who eats animal-based foods.
Important to know:
While excessive intake of retinol from supplements or organ meats can be toxic, carotenoids from plants are not considered dangerous – the body converts them only as needed. This explains why “orange” foods like sweet potatoes or carrots cannot cause vitamin A poisoning – at most, they can cause a temporary orange tint to the skin (carotenodermia), which is purely an aesthetic phenomenon. In other words, eat as many carrots as you want – it’s not harmful to your health.
Foods especially rich in vitamin A
10 notable sources of vitamin A (values per 100 grams of food):
Beef liver – over 9,000 mcg (!) – several times the daily requirement.
Chicken liver – about 3,000 mcg.
Egg yolk – about 140 mcg per unit.
Full-fat cheeses (cheddar, gouda) – around 250–300 mcg.
Butter – about 250 mcg.
Raw carrot – about 835 mcg of beta-carotene (part of which becomes vitamin A in the body).
Orange sweet potato – over 700 mcg.
Pumpkin – about 400 mcg.
Spinach – about 470 mcg.
Sweet red pepper – about 530 mcg.
For perspective: One large carrot or half a cup of cooked spinach already covers almost the entire recommended daily intake.
How does cooking affect vitamin A?
Unlike sensitive vitamins like vitamin C or some B vitamins, vitamin A (and beta-carotene in particular) is not destroyed by heat – on the contrary, our biology allows us to absorb it better after cooking.
This is exactly what makes vitamin A unique:
While other vitamins – like vitamin C or some of the B vitamins – tend to be destroyed by heat and cooking, carotenoids are actually released and become more available to the body. In other words, carrot soup, sweet potato soup, or baked pumpkin not only retain their nutritional value – they actually allow us to absorb it better.
Heating breaks down the cell walls of the plant and increases the bioavailability of the carotenoids. Therefore, cooked carrots or sweet potatoes are actually “stronger” in terms of absorption.
A study published in the Journal of Agricultural and Food Chemistry showed that the bioavailability of beta-carotene in cooked carrots is 2–3 times higher than in raw carrots. In this case, cooking is an advantage rather than a disadvantage – unlike other vitamins that are destroyed by heat.
What else does vitamin A do in the body?
This is the place to note that beyond its important impact on the immune system, this vitamin has several other key roles:
Skin – essential for cell renewal, prevents dryness and flaking.
Hair – deficiency in vitamin A can cause hair loss and scalp dryness.
Night vision – vitamin A is required for the production of rhodopsin, a pigment in the retina responsible for vision in the dark. This is where the myth that “carrots improve eyesight” comes from – they don’t improve daytime vision, but they do prevent night blindness.
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