Last week's report that high doses of vitamin A prevent certain cancers came as no surprise to health-watchers.
Essential for maintenance of normal skin, eyes and tissues that line the mouth, throat and internal organs, vitamin A was also recognized as a possible cancer preventative at least a decade ago: People who consumed a lot of it were found to be less likely to have cancer than were people with low intake.
The first human experiment in which the suspected cancer-preventing power was demonstrated was at the M. D. Anderson Cancer Center in Houston, Texas, and was reported in the New England Journal of Medicine last week.
Patients in the study had already had a head or neck cancer, and although they had been treated, they were regarded as being at high risk of developing another malignancy.
Whether physicians will immediately begin to recommend vitamin A supplements for people at risk of cancer remains to be seen.
While it's hard to overdose on vitamin A from food-based sources -- such as liver, dairy foods and eggs -- excessive amounts of it are known to be toxic.
The particular form used in the experiment is known generically as "isotretinoin," given in pill form. Some people in the experiment had to drop out when their skin dried out and peeled, their blood-fat level rose, or they developed inflammation in the eyes.
Isotretinoin, which is marketed as the anti-acne drug Accutane, has also been associated with birth defects when taken by pregnant women.
"In head and neck cancers, the patients tend to be older, and they are at very high risk of developing a second cancer. So using a medicine like Accutane may be very appropriate," says Dr. James Keogh.
Dr. Keogh is director of a project at University of Maryland Hospital that aims to compare the cancer-preventing power of vitamin A and beta carotene, a vegetable pigment found in carrots, sweet potatoes, apricots and other orange-colored foods, and in dark green vegetables, where its color is hidden by chlorophyll. Beta carotene is converted to vitamin A in the body; it also appears to have some cancer-fighting powers of its own.
Dr. Keogh's study, which will enroll about 800 men at risk of lung cancer because of cigarette smoking and asbestos exposure, is part of a larger project, sponsored by the National Cancer Institute and coordinated by the University of Washington in Seattle.
"If you are trying to prevent a common cancer, and you are asking a large number of people to take a chemical agent, you need to have an agent that's very, very safe," Dr. Keogh says. It may just be that beta carotene will turn out to be that agent. In humans, its only known ill effect is its tendency to produce a yellowish-orange stain in the skin.
However, last week's New England Journal also carried a report of a study in which beta carotene pills proved ineffective in preventing skin cancer in people at risk.
But Dr. Keogh remains optimistic. "Lung isn't skin," he points out. "There is good reason to think beta carotene would work in the lungs based on retrospective studies of diet. That is, people with lung cancer consumed less of it."
The study is still in need of volunteers. Men 45 to 69 years old, with significant asbestos exposure or presence of asbestosis and a history of cigarette smoking, can call 328-6178 for more information.