Vitamin A was one of the earliest vitamins to be discovered – hence its top rank in the alphabetical vitamin nomenclature.Vitamin A is a family of fat soluble compounds that play an important role in vision, bone growth, reproduction, and immune system regulation. Most people associate vitamin A with carrots, and for good reason: the common orange veggie has high amounts of beta-carotene, which is actually a vitamin A precursor and also the reason carrots got their name. But vitamin A is actually a group of chemicals that are similar in structure, and include retinol (the most biologically active form of vitamin A), retinal, and retinoic acid.
β-carotene is slightly different in that it is cleaved in the intestinal mucosa by an enzyme to form retinol. Other carotenoids include lycopene and lutein but, although similar to vitamin A, they are not actually vitamin A in the truest sense. One distinction is that excessive amounts of vitamin A from over-supplementation, can cause toxicity (although deficiency is much more common). On the other hand, β-carotene does not cause vitamin A toxicity because there exists a regulatory mechanism that limits vitamin A production from beta carotene when high levels are ingested.
A large number of physiological systems may be affected by vitamin A deficiency which is most often associated with strict dietary restrictions and excess alcohol intake. Patients with Celiac disease, Crohn’s disease and pancreatic disorders are particularly susceptible due to malabsorption. Vitamin A is also essential for the developing skeletal system and deficiency can result in growth retardation or abnormal bone formation.
The functions of vitamin A are very diverse:
- Eyesight: Vitamin A forms retinal, which combines with a protein (rhodopsin) to create the light-absorbing cells in the eye. This explains why a common clinical manifestation of deficiency is night blindness and poor vision.
- Skin: In addition to promoting healthy skin function and integrity, vitamin A regulates the growth of epithelial surfaces in the eyes and respiratory, intestinal, and urinary tracts. Deficiency impairs epithelial regeneration, which can manifest as skin hyperkeratization, infertility, or increased susceptibility to respiratory infections.
- Anemia: Vitamin A helps transfer iron to red blood cells for incorporation into hemoglobin; thus, a vitamin A deficiency will exacerbate an iron deficiency.
- Weight management: Vitamin A reduces the size of fat cells, regulates the genetic expression of leptin (a hormone that suppresses appetite), and enhances the expression of genes that reduce a person’s tendency to store food as fat.
- Cancer prevention: Vitamin A deficiency impairs the body’s ability to launch cell-mediated immune responses to cancer cells. Vitamin A inhibits squamous metaplasia (a type of skin cancer) and inhibits breast cancer cell growth.
- Fertility: Vitamin A plays a key role in the synthesis of sperm.
- Autism: Vitamin A is part of the retinoid receptor protein (G-alpha protein), which is critical for language processing, attention, and sensory perception. Some autistics have a defect in this protein that vitamin A supplementation can modulate.
- Sleep: Vitamin A deficiency alters brains waves in non-REM sleep, causing sleep to be less restorative.
Vitamin A also interacts with other micronutrients. For example, zinc is required to transport vitamin A into tissues, so a zinc deficiency will limit retinal binding protein (RBP) synthesis and thus limits the body’s ability to use vitamin A stores in the liver. Oleic acid, a fatty acid found in olive oil, facilitates the absorption of vitamin A in the gut.
Find out if you have a vitamin A deficiency, and take steps to correct it, by ordering a micronutrient test today.