Vitamin A is a fat-soluble nutrient essential for vision, immune defense, and cell growth. It comes in two dietary forms: preformed vitamin A (called retinol) found in animal foods, and provitamin A carotenoids like beta-carotene found in colorful fruits and vegetables. Your body converts both into two active compounds, retinal and retinoic acid, which do the actual work in your cells.
Two Forms, Two Sources
The distinction between the two forms of vitamin A matters because they behave differently in your body. Preformed vitamin A, primarily retinol and its storage form retinyl esters, comes ready to use from animal sources like dairy, eggs, fish, and organ meats. Your body absorbs it directly in the small intestine.
Provitamin A carotenoids are plant pigments. The most well-known is beta-carotene, but alpha-carotene and beta-cryptoxanthin also count. Your intestine converts these into retinol using a specific enzyme, but the conversion is inefficient. It takes about 6 micrograms of beta-carotene to produce the equivalent of just 1 microgram of retinol. For other provitamin A carotenoids like alpha-carotene, the ratio is even steeper: 12 to 1. This is why nutrition labels use a unit called Retinol Activity Equivalents (RAE) to put both forms on equal footing.
Not all carotenoids become vitamin A. Lycopene (in tomatoes), lutein, and zeaxanthin (in leafy greens) are non-provitamin A carotenoids. They have their own health benefits, but they won’t raise your vitamin A levels.
How Vitamin A Powers Your Vision
Vitamin A’s role in eyesight is its most famous function, and the mechanism is remarkably specific. In your retina, retinal (the active form) binds to a protein called opsin, forming a light-sensitive pigment called rhodopsin. When light hits rhodopsin, the retinal molecule changes shape, triggering an electrical signal that your brain interprets as vision.
After that burst of activity, the retinal is released, recycled back to its original shape in supporting cells behind the retina, and reloaded into opsin to detect light again. This cycle happens continuously and depends on a steady supply of vitamin A. Without enough, your eyes struggle to adapt in low light, which is why night blindness is one of the earliest signs of deficiency.
Immune System and Skin Barriers
Vitamin A plays a less visible but equally important role in immunity. It helps maintain the mucus-producing linings of your respiratory tract, intestines, and urinary tract. These mucous membranes are your body’s first physical barrier against bacteria and viruses. Vitamin A promotes mucin secretion, the slippery substance that traps pathogens before they can penetrate deeper tissue. When vitamin A is lacking, these linings can dry out and shift toward a skin-like texture through a process called squamous metaplasia, losing their ability to function as barriers. This is one reason vitamin A deficiency in children is closely linked to respiratory infections and diarrhea.
Beyond physical barriers, vitamin A influences how immune cells develop. Retinoic acid, one of its active forms, helps steer immature immune cells toward becoming regulatory T cells, which prevent your immune system from overreacting and attacking your own tissues. At the same time, it suppresses the development of certain inflammatory immune cells. This balancing act is critical for keeping immune responses proportional to actual threats.
Best Food Sources
Animal sources deliver preformed vitamin A and are the most concentrated options. Beef liver is by far the richest source, followed by other organ meats, herring, salmon, eggs, and dairy products like milk and cheese. A single serving of beef liver can provide many times the daily requirement, which is worth noting because it also makes overconsumption possible.
For plant-based sources, color is your guide. Deep orange and dark green signal high beta-carotene content:
- Orange vegetables: sweet potatoes, carrots, winter squash
- Dark leafy greens: spinach, broccoli
- Fruits: cantaloupe, mangos, apricots
- Fortified foods: many breakfast cereals have added vitamin A
Because vitamin A is fat-soluble, your body absorbs it much better when you eat it with some dietary fat. Research on absorption shows that including even a modest amount of fat in a meal, around 5 to 10 percent of calories, significantly improves uptake. In practical terms, cooking carrots in a bit of olive oil or eating spinach salad with an oil-based dressing makes a real difference compared to eating those vegetables with no fat at all.
How Much You Need
The recommended daily intake for adults is 900 mcg RAE for men and 700 mcg RAE for women. During pregnancy, the recommendation rises to 770 mcg RAE, and during breastfeeding to 1,300 mcg RAE. Infants need far less, around 400 to 500 mcg RAE depending on age. Most people eating a varied diet that includes some animal products or colorful produce meet these levels without supplements.
What Deficiency Looks Like
Vitamin A deficiency is rare in developed countries but remains a serious public health issue in parts of Africa and Southeast Asia, particularly among children. The progression in the eyes, collectively called xerophthalmia, follows a pattern that ranges from mild to devastating.
Night blindness is typically the earliest symptom, reflecting a shortage of retinal for the rhodopsin cycle. The conjunctiva, the clear membrane over the white of the eye, can develop dry patches and characteristic white, foamy deposits called Bitot’s spots. These spots are made of keratin, a tough protein the conjunctiva starts producing when it loses its normal mucous membrane character.
In acute, severe deficiency, the cornea itself dries out because tear-producing glands stop working normally. If not reversed urgently, the cornea can ulcerate and literally melt away through a process called keratomalacia, sometimes destroying the eye in just a few days. The damage is usually symmetrical, affecting both eyes. The end result can be permanent corneal scarring or total blindness. Importantly, these stages don’t always happen in a neat sequence. A child can develop corneal destruction without ever showing Bitot’s spots if the deficiency is sudden and severe.
Risks of Getting Too Much
Vitamin A toxicity, called hypervitaminosis A, comes exclusively from preformed vitamin A, not from beta-carotene. Your body regulates the conversion of carotenoids, so eating large amounts of carrots or sweet potatoes won’t cause toxicity (though it can temporarily turn your skin orange, a harmless condition called carotenemia).
The tolerable upper intake level for preformed vitamin A in adults is 3,000 mcg RAE per day. Chronic intake above this level, usually from supplements or very frequent consumption of liver, can cause nausea, headaches, dizziness, blurred vision, and joint pain. Over time, excess vitamin A accumulates in the liver and can cause lasting damage, including liver toxicity and reduced bone density. Pregnant women face an additional risk: high doses of preformed vitamin A are linked to birth defects, which is why prenatal supplements typically use beta-carotene instead of retinol.
Vitamin A Derivatives in Medicine
Synthetic forms of vitamin A, called retinoids, are widely used in dermatology. Topical retinoids are a cornerstone treatment for acne and skin aging, working by speeding up skin cell turnover and preventing clogged pores. Oral retinoids are prescribed for severe acne and have also shown benefit in treating rosacea, with studies finding they reduce inflammatory bumps and redness over roughly 16 weeks of treatment. These medications require medical supervision because they carry the same toxicity risks as high-dose preformed vitamin A, including the potential for birth defects.