Most adults with blinding retinitis pigmentosa (RP) should take a daily, 15,000 IU vitamin A supplement, based on results from a large, randomized clinical trial published today in the Archives of Ophthalmology.
This recommendation is the first from a well-designed clinical trial indicating that people can be treated for this retinal disease. “This is exciting news,” said Carl Kupfer, M.D., director of theNational Eye Institute, which supported the six-year study. “While vitamin A supplementation certainly does not represent a cure, it does signify a first step in managing these diseases.”
Eliot L. Berson, M.D., the study’s principal investigator and professor of Ophthalmology at Harvard Medical School, said that adults who supplemented their diets with 15,000 IU of vitamin A daily had on average about a 20 percent slower annual decline of remaining retinal function than those not taking this dose.
Based on this finding, Dr. Berson and his colleagues estimated that an average patient in the study who started taking a 15,000 IU vitamin A capsule at age 32 would retain some useful vision until age 70, whereas a patient not on this dose would lose useful vision at age 63.
The investigators also recommended that adults with RP should avoid taking high-dose vitamin E supplements. In the study, the disease appeared to progress faster on average in patients on a daily, 400 IU vitamin E supplement than in those taking a trace amount of the vitamin. Dr. Berson said that the study showed no evidence that normal dietary or small supplemental amounts of vitamin E have an adverse effect on the disease.
Retinitis pigmentosa is a group of inherited retinal diseases that affects about 100,000 Americans and 1.5 million people worldwide. It causes the progressive deterioration of specialized, light-absorbing cells in the retina, the paper-thin tissue that lines the back of the eye like film in a camera.
As these cells slowly degenerate, people with RP develop night blindness and a gradual loss of peripheral vision. By about age 40, most have tunnel vision, although many may retain good central vision. Between the ages of 50 and 80, however, they typically lose their remaining sight. The extent of vision loss in people of the same age as RP may be different.
Dr. Berson stressed that adults considering vitamin A supplementation should first:
- Consult with their eye care professional about vitamin A supplementation.
- Have their blood level of vitamin A measured before starting treatment. If people have pre-existing liver disease or abnormally high blood levels of vitamin A, they will need to adjust their vitamin A intake.
- Take vitamin A palmitate, as this was the form of the vitamin studied. Supplements of beta-carotene, a natural precursor of vitamin A, are not a predictable source of the vitamin since each person breaks down beta-carotene differently.
- Make a point of eating a balanced diet, without selecting foods that are especially high in vitamin A.
- Avoid taking high-dose vitamin E supplements.
“One of my biggest concerns is that people will make the mistake of thinking that vitamin A supplementation in excess of the the15,000 IU recommended will provide even greater benefit,” said Dr. Berson. “We have evidence in fact that supplementation of a regular diet with greater than 15,000 IU of vitamin A does not provide greater benefit. Moreover, a daily vitamin A intake exceeding 25,000IU over the long term can be toxic in adults and may cause side effects such as liver disease.
“Our interpretation of the study results is that the course of the common forms of retinitis pigmentosa is slower on average among adult patients on a regular diet who take a daily, 15,000 IU vitamin A supplement in the palmitate form compared with the course of those patients not on this supplement,” he said.
Because the study involved adults between the ages of 18 and 49, no formal recommendations can be made for patients under the age of 18.
Dr. Berson warned that women with RP should not take 15,000 IU vitamin A supplements during pregnancy because high doses of vitamin A have been linked to birth defects.
A single capsule containing 15,000 IU of vitamin A in the palmitate form will soon be available commercially. For further information on its availability, Contact the RP Foundation Fighting Blindness*toll-free at 1-800-683-5555.
Background Information on the Study
This study was a prospective, double-masked clinical trial (neither the patient nor the clinician knew to which treatment group the patient had been assigned). It was designed to assess the effectiveness of vitamin A and/or E supplements in halting or slowing the progression of RP.
An independent Data Safety and Monitoring Committee provided advice to the investigators and monitored the accumulating data on a regular basis for evidence of harm or benefit to study participants.
A total of 601 RP patients from across the United States and Canada were enrolled in the study. All were in good general health, between the ages of 18 and 49, and entered the study with different initial levels of retinal function. Following an examination, participants were assigned randomly to one of four treatment groups:
- 15,000 IU vitamin A + 3 IU vitamin E
- 75 IU vitamin A + 3 IU vitamin E
- 15,000 IU vitamin A + 400 IU vitamin E
- 75 IU vitamin A + 400 IU vitamin E
Thereafter, the researchers examined each patient annually, with a mean follow-up time of 5.2 years. The electroretinogram (ERG) was used as the study’s primary outcome measure. The ERG is a light-evoked electrical response from the retina that can be accurately measured using a special Contact lens, much like an electrocardiogram measures coronary function. An ERG provides an objective measure of a person’s retinal function. The scientists also used visual fields and visual acuity as additional measures of visual function.
This clinical trial was conducted at the Berman-Gund Laboratory for the Study of Retinal Degenerations at the Massachusetts Eye and EarInfirmary in Boston, Massachusetts. It was supported by the NationalEye Institute and, in part, by the RP Foundation Fighting Blindness*in Baltimore, Maryland. The National Eye Institute, a part of theNational Institutes of Health, is the Federal government’s lead agency for the conduct and support of research on the human visual system in health and disease.
*RP Foundation Fighting Blindness is now called the Foundation Fighting Blindness.
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Citations
- Berson EL, Rosner B, Sandberg MA, Hayes KC, Nicholson BW, Weigel-DiFranco C, Willett W. A Randomized Trial of Vitamin A and Vitamin E Supplementation for Retinitis Pigmentosa. Arch Ophthalmol. 1993 Jun. PubMed