Large daily doses of vitamin A can slow the slide toward blindness for patients with retinitis pigmentosa and may save years of eyesight for 100,000 Americans with the inherited affliction, a new study indicates.
Dr. Eliot L. Berson, a Harvard Medical School researcher, said a dietary study of 600 patients with retinitis pigmentosa, or RP, showed that vitamin A therapy slowed the loss of eyesight.
He said a patient who started vitamin A therapy at age 32 could retain vision until age 70 instead of losing sight at age 63.
The same study also showed that large, supplemental doses of vitamin E actually accelerate the RP disease, Berson said.
At one time, he said, it was thought that both vitamin A and E were beneficial.
"The course of disease was slowed, on average, among adults with the common form of RP who took vitamin A," said Berson in an interview. "There was a suggestion of a more rapid rate of decline among those taking 400 international units of vitamin E."
A report on the study is published this week in the Archives of Ophthalmology.
Achieving the beneficial effect requires daily doses of 15,000 international units, or IU, of vitamin A.
Berson said only vitamin A derived from palmitate was proven in the study to be beneficial.
He said beta-carotene, a vitamin A precursor, does not have the same predictable effect.
The researcher emphasized that all patients should consult with their doctors before starting the vitamin supplements.