By Eva Briggs, MD
You may have heard our new secretary of health and human services touting vitamin A as a treatment for measles. It’s not effective unless the patient is deficient in vitamin A. So, what is vitamin A and what is its function?
Vitamins are molecules that the body requires in small quantities in order for metabolism to work properly. Scientists suspected a substance of some type was required for health as far back as 1819, when French physiologist François Magendie observed that malnourished dogs developed corneal ulcers and were at increased risk of death. Other scientists eventually identified and isolated the substance in the early 1900s and in 1920 it was named vitamin A.
Vitamin A, along with vitamins D, E and K, is fat soluble. This means that dietary fat is required for its absorption. Retinol, a form of vitamin A, is found in fish, meat and dairy products. Beta-carotene, a red-orange pigment found in plants, is a proto-vitamin. This means the body can convert it into the active form of vitamin A. Common sources are carrots, cantaloupe, spinach and other dark green leafy vegetables and winter squash.
Dietary retinol is commonly attached to a fatty acid molecule, forming retinyl esters. Enzymes in the intestines break the retinyl esters back into the components: retinol plus a fatty acid molecule. Then the retinol passes into the body. Humans don’t have a mechanism to suppress absorption of excess vitamin A or to excrete the surplus in the urine. This is why too much vitamin A accumulates and reaches toxic levels. For example, polar bear liver contains very high concentrations of vitamin A. People have become sick with vitamin A excess after eating polar bear liver.
There are three syndromes associated with too much vitamin A. Acute vitamin A toxicity happens when someone consumes excessive vitamin A over a short period, commonly from supplements or high-dose supplements. (Or rarely polar bear liver.) Symptoms include liver injury, nausea, vomiting, headache, dizziness, blurred vision and incoordination. Chronic vitamin A toxicity occurs when a patient takes in too much vitamin A over a prolonged period. This can happen either from dietary sources such as too much liver or from long-term use of vitamin A supplements. Symptoms include skin and nail damage, bone and joint pain, fatigue, enlarged liver and bone injury such as osteoporosis and hip fractures. Birth defects, called teratogenesis, is the third syndrome of excess vitamin A. Affected children may have central nervous system defects, heart malformations, facial abnormalities and urinary tract issues.
The correct amount of vitamin A has many functions in the human body. It affects the eyes in two ways. Vitamin A is essential for synthesizing the pigments in the retina. An early sign of vitamin A deficiency is night blindness. Vitamin A is also important for the cells that form the surface of the conjunctiva and cornea. Vitamin A deficiency can cause corneal ulceration and blindness. Normal vitamin A levels promote immune function.
Low vitamin A levels can leave individuals susceptible to infectious diseases.
This is where the idea that vitamin A treats measles arises.
Yes, in areas where vitamin A deficiency is common, supplementation helps patients combat measles. But vitamin A deficiency is rare in United States. Extra vitamin A won’t help those who are not deficient but too much lead to illness as described above. In fact, there have already been cases of children with vitamin A toxicity in Texas due to at-home attempts to treat measles.
There is one thing proven to prevent measles. That’s vaccination.
Eva Briggs is a retired medical doctor who practiced in Central New York for several decades. She lives in Marcellus.