How vitamin A moves through your body

Two foods, two starting points

Imagine a carrot beside a bottle of cod liver oil. Both can contribute to vitamin A nutrition, but the carrot supplies beta-carotene—a pigment that can be converted into vitamin A—while cod liver oil contains preformed vitamin A. The amount converted from a plant food varies. Other carotenoids, such as lutein and zeaxanthin, do not become vitamin A.

This journey is a simplified account of common pathways, not a measure of exactly where every molecule goes. For food choices and the evidence on preparation, start with carrots, retinol and absorption.42

At the small intestine: absorption and conversion

Digestion releases vitamin A forms and carotenoids from food. Preformed retinyl esters are broken down to retinol before uptake by cells lining the small intestine. Inside those cells, some absorbed beta-carotene can be converted into retinal and then retinol; some carotenoid can be absorbed without being converted. Absorption and conversion depend on the food and the person.

Fat digestion helps with absorption, but this does not establish a fixed amount of fat to add to a particular meal or supplement. Follow the product’s actual instructions and use the guide to taking vitamins with food for the separate question of timing.32

A ride through lymph and blood

The intestinal cells package much of the newly absorbed vitamin A as retinyl esters inside particles called chylomicrons. Think of these as tiny packages that carry dietary fat and other materials. They travel first through lymph—a fluid-transport system—and then enter the blood. Some material can reach other tissues before the remaining particles are taken up by the liver; there are other pathways too.32

Why does the liver store vitamin A?

The liver is a major storage site. It can put retinol into a storage form called a retinyl ester and later release retinol for use elsewhere. Storage helps the body cope with variation in intake; it is not unlimited and does not make excess harmless. Repeated high intake of preformed vitamin A can cause harm.

The question is especially important for pregnancy and planning: product type and local advice matter. See vitamin A, pregnancy and planning and what too much vitamin A means.34

How does stored vitamin A reach other tissues?

When retinol leaves the liver, it commonly travels in blood attached to retinol-binding protein, a carrier. A second protein, transthyretin, can join that complex. Cells can take up retinol and turn it into other forms. This is a useful main route, not the only way vitamin A can reach tissues.

Blood retinol is regulated over much of the range of liver stores and can be affected by illness. A single result does not reveal a person’s whole vitamin A picture; a clinician interprets it with symptoms, history and other findings. See deficiency, sight and blood tests.25

In the eye: retinal helps detect light

In the retina—the light-sensitive layer at the back of the eye—a form called retinal combines with proteins to make light-sensitive pigments. Rod cells, important in dim light, use a pigment called rhodopsin. Light changes retinal’s shape and starts a chain of signals; a recycling process restores the light-sensitive form.

Deficiency can impair night vision, but difficulty seeing at night has other causes. If you suddenly cannot see from one or both eyes, or have sudden severe eye pain, seek emergency care immediately. Having enough vitamin A for normal vision is not proof that extra supplements improve the sight of someone who is not deficient. The night-vision guide explains what else to consider.641

Elsewhere: retinoic acid helps regulate cells

In many tissues, cells convert vitamin A into retinoic acid, a form that helps control the activity of genes—the instructions cells use to make proteins. This is one way vitamin A contributes to normal growth, surface barriers and immune function. Retinoic acid is one member of a broader retinoid family; nutritional vitamin A is not interchangeable with a prescription retinoid medicine.

A role in normal biology does not establish that extra vitamin A prevents infection or improves skin. Explore immunity claims and food, skincare and retinoid medicines for the different evidence.34

What can change the journey?

Food structure and preparation, fat absorption, underlying conditions and medicines can change what is absorbed or how it is handled. Orlistat can affect absorption of fat-soluble nutrients. The US Xenical label reports reduced absorption of beta-carotene supplements and a vitamin E acetate supplement, but says its effect on supplemental vitamin A absorption is unknown. Oral retinoid medicines raise a different question about overlapping effects. These are not instructions to change a medicine or add a supplement.247

Use the medicine-interaction guide and bring the exact product and medicine list to a pharmacist or prescriber for an individual question.

Where to go next

For a quick refresher, return to the vitamin A overview. If you are comparing a multivitamin and cod liver oil, the label guide shows how forms and serving sizes can overlap. If your vision changes, seek urgent professional advice rather than assuming a cause; new flashes or a dark shadow are examples needing prompt assessment. The night-vision guide provides background; sudden inability to see or sudden severe eye pain needs emergency care immediately.1