Wonders of Vitamin A Being Uncovered : Science: Inexpensive chemical works against infant mortality, blindness and measles. Laboratories find genetic and cellular functions.
There are very few wonder drugs in the world, but Vitamin A may be one of them.
This dirt-cheap chemical can lower childhood mortality by about one-third in vast parts of the developing world. It prevents keratomalacia, one of the five leading causes of blindness. It’s the closest thing to a specific treatment for measles. It’s a fairly good therapy for some types of anemia. It may reduce the transmission of the AIDS virus from mother to fetus.
It’s quite safe, it’s easy to store and one dose--good for four months--costs about 2 cents.
And that’s just the practical side of the story.
Information about Vitamin A’s role in the physiology of cells is pouring out of laboratories. Whole new functions are being uncovered.
Vitamin A regulates hundreds of genes. It is a key modulator of the immune system. It helps aim cells along the tricky trajectory from primitive to adult forms, a job that may play some role in preventing the development of cancer.
Overall, Vitamin A is emerging as evolution’s equivalent to the Swiss Army knife.
The substance’s ability to fight infections in malnourished people is its most astounding property. First suggested more than 60 years ago, and proved only in the past decade, the significance of this finding is just beginning to become clear.
“It is one of the most important breakthroughs in public health in the last 50 years,” the retired director general of the Pan American Health Organization, Abraham Horwitz, said recently.
Vitamins are substances that are essential to life but cannot be made from scratch by the organism that needs them. (Many substances actually fit this definition, including some amino acids that form the building blocks of proteins. The difference is that, unlike amino acids, vitamins are required only in tiny amounts. They act more as catalysts for biochemical reactions than as raw materials for biological construction.)
Vitamin A--unlike Vitamin C and the B vitamins--is “fat-soluble” and can be stored in body tissue for prolonged periods. This raises the risk of toxic effects, but offers one particular advantage. Intermittent doses, acquired either through diet or pharmacological supplements, can tide an organism over many fallow months.
In many diets, Vitamin A deficiency is never a threat. Nevertheless, dietary sources seem to be insufficient in many parts of the world.
Marginal intake is worsened by frequent infection, which depletes the body’s Vitamin A stores.
Butter, egg yolk and liver contain large amounts of Vitamin A. Equally important sources are yellow and orange fruits and vegetables (such as squash, sweet potatoes and papayas), and dark-green, leafy vegetables. They contain large amounts of beta-carotene, a compound split by the body into two molecules of retinyl palmitate, Vitamin A. The latter gives rise to a family of derivatives known as “retinoids.”
Since its discovery in 1913, Vitamin A has been regarded mostly as the vitamin of vision. A compound called retinal is essential for making the light-sensing biochemicals in the retina, or back wall, of the eye.
Vitamin A deficiency shows itself, early on, as night blindness.
Curiously, the vitamin’s more medically important role in vision involves a different part of the eye. Severe deficiency causes the cornea--the clear cover of the eye’s front--to melt away, leaving behind opaque scar tissue and permanent blindness.
Vitamin A’s anti-infective uses were discovered--or, to be precise, rediscovered--in the early 1980s by Alfred Sommer, an epidemiologist working in Indonesia who is now dean of the Johns Hopkins School of Hygiene and Public Health.
Vitamin A deficiency--at least as measured by subtle changes in the appearance of the eye--occurred inconsistently in Javan villages. Some children showed signs of it while their neighbors showed none. Sommer and his colleagues sought reasons for these differences in the diets and frequency of illnesses (such as diarrhea) in a group of 4,000 preschoolers.
The researchers observed the children for several years and noticed something they had not expected to see. There was a clear relationship between Vitamin A deficiency and mortality. Moreover, there appeared to be a “dose-response” relationship: The more advanced the eye problems, the higher the death rate. (Children with severe eye changes were removed from the study and immediately given Vitamin A. None went blind.)
The team already had plans to conduct a study of 26,000 Sumatran children, half of whom would be given Vitamin A supplements and half of whom would not. Besides looking for eye changes in both groups, they quickly added illness and mortality as “endpoints” they also would measure. At the end of a year, mortality in the Vitamin A group was 34% lower than in the control group.
A simultaneous study that the Sommer team ran on Vitamin A supplementation in children hospitalized with severe measles showed even more dramatic results: a drop of 50% in deaths from the disease.
The studies appeared in 1986 and 1987 in The Lancet and the British Medical Journal. As it happens, the latter journal in 1932 had published a study showing that death rates from measles could be cut by 58% if ill children were given cod-liver oil, which is high in Vitamin A. The place where this research was done?
A hospital in London.
“As best as one can tell, nothing else appeared on the subject,” Sommer said of that experiment. “It did not change clinical practice. Some things people are willing and ready to accept, and some things they aren’t, even with the evidence.”
Vitamin A’s importance in other infections is emerging.
A paper published last year reported increased mortality (and greater immune depression) among HIV-positive drug users in Baltimore who were mildly deficient in Vitamin A. One published in June showed that pregnant, HIV-infected women in Malawi transmitted the virus to their babies 32% of the time if they were severely Vitamin A deficient, but only 7% of the time if they had sufficient stores of the vitamin.
There is little data to suggest Vitamin A supplements are helpful in people who are not deficient. Excessive doses, in fact, can be toxic, and occasionally fatal.
Nevertheless, the World Health Organization estimates there are about 250 million children who are not getting as much Vitamin A as they need. A major effort is under way to right this.
