The Power of A
Last year, when Dr. Gloria De Carlo Massaro published a study suggesting that vitamin A could be used to grow lung tissue in newborn rats, phones rang off the hook from desperate patients seeking a cure for emphysema. Sorry, she said, human studies are years away, and tinkering with this particular vitamin could be dangerous.
She and her colleagues at the Georgetown University School of Medicine have spent the last year doing studies on adult rats with emphysema-like damage in their lungs. Again, vitamin A allowed the damaged air sacs, called alveoli, to return to their normal size and number, according to a study published recently in Nature Medicine.
Although human studies are still years away and over-supplementation is every bit as ill-advised as ever, the new research joins a growing body of evidence of the power of this vitamin that scientists are just beginning to understand.
“It’s a very interesting, important compound and has a lot of therapeutic potential,” said Dr. Robert Russell, director of human study at the U.S. Department of Agriculture’s Nutritional Research Center at Tufts University.
Indeed, the vitamin and its metabolites are being studied as potential therapies for cancer, macular degeneration (an eye disease) and possibly as a way to boost the immune system.
Although the fat-soluble vitamin is under investigation in several research labs across the country, public health experts caution that excess vitamin A could cause damage to the liver and other organs, and supplements should be used judiciously, if at all.
In fact, Dr. William Sommer, dean of the Johns Hopkins School of Public Health and a world leader on vitamin A, said there seems to be no health benefits gained from gulping vitamin supplements. The normal amount is 1,800 international units a day. But Americans consume three to four times this in their diet alone.
Scientists also have found that a derivative of vitamin A, beta carotene, may even put smokers at increased risk of lung cancer. This surprised many researchers banking on the cancer-preventive properties of the vitamin. Researchers are still trying to figure out why this risk occurs.
“If we could figure out how to manipulate the good qualities of the vitamin, we’d have a terrific cancer treatment,” Russell said.
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Scientists have known since the 1950s that vitamin A plays an important role in vision. By the 1970s, researchers discovered that a major cause of childhood blindness in Third World countries was vitamin A deficiency. Half a million children a year were becoming blind because the lack of vitamin A melted the cornea, the front clear part of the eye. Still, no one knows why.
This finding has led to commitments to provide vitamin A to children worldwide, at a cost of 2 cents a day each. Milder vitamin A deficiencies have more recently been linked to night blindness as well.
But Sommer and his colleagues found during years of study overseas that many children, even some who had no signs of eye disease, were actually dying from a lack of vitamin A.
The doctors cut mortality by one-third when they began providing one capsule every four months to children younger than 6. Countries now routinely providing vitamin A have virtually eliminated vitamin A-related blindness and death.
Still, vitamin A deficiency remains a big problem outside the United States. In some parts of the world, 20% to 50% of adults are lacking in the vitamin, doctors say.
Sommer’s team also discovered that providing a two-day dose of vitamin A reduced measles deaths by half. The reason: The vitamin is involved in raising a healthy immune response. The American Academy of Pediatrics now recommends vitamin A in the treatment protocol for measles.
The Hopkins doctor is now conducting a study in which pregnant women are provided with a supplement in hopes of reducing maternal deaths during childbirth. Pregnant women with AIDS are also taking the vitamin in another study. “We really think we can do something to prevent the transmission of AIDS,” Sommer said.
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Vitamin A and its metabolites appear to have potent antioxidant properties. That means they prevent the formation of toxic cell-damaging free radical molecules. When it was observed that people who ate beta carotene-rich diets had lower incidences of chronic disease, including cancer, scientists set out to study whether megadoses of the vitamin would have the same impact.
Three studies found no difference between those taking beta carotene supplements and those on a placebo pill. And last year, two studies--one in the United States and one in Finland--reported that smokers who had received the beta carotene supplements actually had developed lung cancer more often than those on placebo. There were more deaths also.
The studies were halted immediately, but researchers still remain puzzled by the results. Russell suspects the answer lies in the dosage, which was 10 times that found in a healthy vitamin A-rich diet. “We are trying to figure out why this happens so mistakes like this don’t happen again,” Russell said.
Russell and his colleagues have found that retinoic acid, the vitamin A derivative used in the emphysema rat study, binds to specific receptors and turns on several genes in the body. One of these genes is the tumor-suppressor gene that, if not turned on, could put people at risk for cancer, Russell said.
Ultimately, he said, scientists are working on manipulating these derivatives to trigger only the cancer-fighting benefits without any of the side effects. In high doses, vitamin A can cause brittle nails, hair loss, headaches and liver damage.
