Vitamin slows advancing blindness from RP.
"This is exciting news;' says Carl Kupfer, director of the National Eye Institute in Bethesda, Md. Worldwide, roughly one in every 4,000 persons suffers from the disease.
Adds Alan M. Laties, chairman of the RP Foundation's scientific advisory board, "Although not a cure, [vitamin A supplementation] will improve the quality of life, potentially adding many years of useful vision."
While monitoring RP patients in the early 1980s, ophthalmologist Eliot L. Berson and his co-workers identified a small group who had been supplementing their diet with large amounts of vitamin A, vitamin E, or both. And compared to patients taking ordinary multivitamin supplements or no supplements at all, those taking high doses of A or E sustained far less retinal degeneration over a two-year span, as measured by an electroretinogram (ERG). This test determines the health of photoreceptors by measuring electrical activity o! the eye's photoreceptor cells, known as rods and cones.
The finding intrigued Berson, of the Berman-Gund Laboratory for the Study of Retinal Degenerations at Harvard Medical School in Boston, because high ERG values correlate with healthy photoreceptors. However, since most of the megavitamin users took both A and E, Berson's team couldn't determine the relative value of the vitamins.
So they initiated a six-year study of 601 RP patients between age 18 and 49. The researchers randomly assigned each patient to one of four daily supplements: 15,000 international units (IU) of vitamin A in the form of retinyI palmitate; 15,000 IU of A plus 400 IU of vitamin E; 400 IU of vitamin E; or trace amounts of both vitamins. Annually, the Harvard researchers assessed ERG values, visual field (peripheral vision), and visual acuity in each patient. Neither patients nor doctors knew which treatment any individual had received.
In the June ARCHIVES OF OPHTHALMOLOGY, Berson's team reports finding a slower drop-off in ERG values among patients receiving 15,000 IU of vitamin A. Those getting large amounts of both vitamins did less well, but better than patients receiving just trace amounts of each.
The big surprise, Berson says, was that retinal degeneration proceeded most quickly in patients given vitamin E supplements. Although the data weren't powerful enough to prove that E posed a risk to patients with the most advanced retinal degeneration at the start of the study, Berson says that "anybody reading this paper would conclude that RP patients shouldn't take high doses of E:'
Overall, the new data suggest, the average RP patient in this study beginning vitamin A therapy at age 32 will retain some useful vision until age 70 -- seven years longer than one taking no supplements and 12 years longer than a patient taking 400 lU of vitamin E daily, Though the Harvard researchers now recommend vitamin A therapy for most RP patients, they caution against taking any form but the palmirate - and then only under an ophthalmologist's supervision.
Vitamin A plays a functional role in sight by latching on to a protein in the rods and cones. When exposed to light, the vitamin changes shape -- the initial step in relaying light-detection signals t0 the brain. "But the mechanism by which vitamin A helps the retina in this disease remains unknown." Berson notes. Vitamin E's role also remains unknown, although Berson's group observed that patients taking vitamin E had lower concentrations of A in their blood, suggesting that E may inhibit the body's absorption or transport of A.
In an accompanying editorial, Robert M. Massof and Daniel Finkelstein of Johns Hopkins University in Baltimore describe the new study as "a tour de force in experimental design, execution, and statistical analysis." However, they advise caution in prescribing vitamin A, arguing that the slower declines in ERG readings of A-supplemented patients may not necessarily translate into a slowing o! their loss of visual function.
Berson disagrees. "The editorial implies that visual field is the last word on how people are doing," he told ScIENcE NEws. "But electrical recording should be the last word -- because it's much more sensitive." Indeed, he argues, ERG data are so sensitive they can detect changes that may take 10 or 15 years to confirm through visual-field tests.