TL;DR

Vitamin A is essential for healthy eyes, skin, mucous membranes, and the immune system. Early deficiency often causes poor night vision and dry eyes. Because vitamin A is a fat-soluble vitamin, people with poor fat digestion, gallbladder problems, or difficulty converting beta-carotene may be at higher risk. Too much vitamin A can be toxic, so supplementation should be used appropriately.

Early Signs of Vitamin A Deficiency:

Early vitamin A deficiency primarily causes night blindness, dry eyes (conjunctival xerosis), and Bitot’s spots (foamy, silvery-grey triangular patches of dead, keratinized squamous epithelial cells on the conjunctiva). Blood levels often remain normal initially because the liver stores large amounts of it. Hyperkeratosis follicularis, which usually manifests as red bumps on the back of the arms, may be another early sign of vitamin A deficiency [1,2].

What Does Vitamin A Do?

Correcting vitamin A deficiency can improve night blindness. It may also help dry, itchy eyes. It is especially valuable for improving the integrity of the mucous membranes, protecting them from viruses and bacteria. Patients who suffer from repeated sinus, upper respiratory, bladder and kidney infections fare better when they have adequate vitamin A.

Vitamin A is a much-neglected vitamin for immune system problems [3-5]. People often take large amounts of vitamin C and never think of taking vitamin A.

Approximately 90 percent of the body’s vitamin A is stored in the liver, with small amounts deposited in the fat tissues, lungs, kidneys and retinas of the eyes. Zinc is needed to mobilize vitamin A out of storage. This is why so many of the symptoms of zinc deficiency are similar to the symptoms of vitamin A deficiency.

What Foods Have Vitamin A?

Good sources of vitamin A include animal products like beef liver, eggs, and fish oils. Brightly colored produce has carotenes, which can be converted to vitamin A. Vegetable sources of vitamin A (carotenes) include squash, cantaloupe, carrots, spinach, and sweet potatoes.

Beta Carotene Is NOT Vitamin A

Carotenes (like beta carotene) must be converted to vitamin A by the body. Poor conversion is very common, affecting roughly 45% to 50% of people due to genetic variations in the BCO1 enzyme. Human studies show that overall conversion rates are highly inefficient and variable, requiring a weight ratio anywhere from 3.8:1 up to 28:1 to manufacture usable retinol [6].

Thyroid hormone (thyroxine) accelerates the conversion of provitamin A carotene into usable vitamin A; an underactive thyroid slows this process down, frequently resulting in high blood carotene levels (carotenemia).

Can Vitamin A Be Toxic?

Vitamin A can be toxic. Symptoms of toxicity include nausea, vomiting, diarrhea, dry skin, hair loss, headaches, appetite loss, sore lips, and flaky, itchy skin. Bone fragility, thickening of long bones, deep bone pain, enlargement of the liver and spleen, blurred vision and skin rashes are symptoms of prolonged excessive intake. It can also lead to reduced thyroid activity and excessive serum calcium.

Early findings of vitamin A toxicity are sparse, coarse hair, alopecia of the eyebrows, dry rough skin and cracked lips. Severe headache, pseudotumor cerebri and generalized weakness are prominent later. Cortical hyperostoses and arthralgia are common, especially in children. Excessive ingestion of carotene does not cause hypervitaminosis A, but produces high carotene levels that can cause carotenosis, which is asymptomatic. In carotenosis the skin, especially the palms and soles. (but not the whites of the eyes) becomes yellow.

Selected References:

  1. The Journal of Nutrition Volume 138, Issue 10, October 2008, Pages 1835-1839 Vitamin A Deficiency and Clinical Disease: An Historical Overview
  2. The Journal of Nutrition Volume 132, Issue 7, July 2002, Pages 1805-1811 The Experimental Induction of Vitamin A Deficiency in Humans
  3. Nutrition Clinique et Métabolisme Volume 36, Issue 2, May 2022, Pages 89-98 Understanding the role of vitamin A and its precursors in the immune system
  4. Green HN, Mellanby E. Vitamin A as an anti-infective agent. Br Med J. 1928;2(3537):691-696.
  5. Influence of vitamin A supplementation on inflammatory biomarkers in adults: a systematic review and meta-analysis of randomized clinical trials. Sci Rep. 2022;12(1):21384.  
  6. The American Journal of Clinical Nutrition Volume 91, Issue 5, May 2010, Pages 1468S-1473S Bioconversion of dietary provitamin A carotenoids to vitamin A in humans
  7. Acta Med Austriaca. 1993;20(1-2):17-20. Beta-carotene, vitamin A and carrier proteins in thyroid diseases