Vitamin A (retinol)

Vitamin A is a fat-soluble vitamin. As preformed retinol it occurs in animal foods such as liver, egg yolk and milk fat; from plants the body takes up precursors such as beta-carotene and converts them as needed. Absorption in the gut requires fat and bile acids. Most of the vitamin A is stored in the liver and released from there to the tissues, bound to retinol-binding protein. Retinol is measured in serum. In the SIBO profile it is looked at because bacterial overgrowth of the small intestine can disturb fat digestion and thus the absorption of fat-soluble vitamins.

What vitamin A does in the body

In the retina, vitamin A is converted into retinal and, together with a protein, forms the visual pigment rhodopsin, which the rods use to see in low light. Another form, retinoic acid, binds to receptors in the cell nucleus and switches genes on and off there. Through this, vitamin A controls how cells of the skin and the mucous membranes in the airways, gut and urinary tract renew and mature, so that these surfaces stay tight and moist. The immune system also depends on it: retinoic acid directs immune cells into the gut lining and promotes the formation of secretory IgA. Vitamin A is also involved in the development of the child in the womb.

Low vitamin A – what happens in the body?

The retinol level in the blood is kept constant for a long time as long as the liver still has reserves. If it falls, the stores are usually largely used up. Less rhodopsin is then formed – the first sign is poor vision at dusk. The conjunctiva and cornea dry out, the skin becomes dry and rough, and the mucous membranes lose their barrier function, which favours infections of the airways and gut. Causes are a low intake, impaired fat absorption, for example with bacterial overgrowth of the small intestine, or disorders of the pancreas and liver. Important for interpretation: during acute inflammation and with zinc deficiency, the liver makes less transport protein, so the blood value falls even though reserves may still be present.

High vitamin A – what happens in the body?

Because vitamin A is fat-soluble and stored in the liver, it can accumulate with a persistently high intake. An excess arises almost only from high-dose preparations or very frequent consumption of liver; beta-carotene from plants does not lead to it, because the body slows down the conversion. Acutely, too much vitamin A can cause headache, nausea and dizziness because pressure inside the skull rises. With a prolonged excess, the liver is strained, the bones lose mineral, skin and lips become dry and the hair thins. In pregnancy an excess can disturb the development of the child. Reduced kidney function also raises the blood value, because the transport protein is excreted more slowly.

The interpretation is given in your report.