Patients with retinitis pigmentosa, a progressive eye disease that can cause vision loss, who were treated with vitamin A and docosahexaenoic acid (DHA), a kind of omega-3 fatty acid, did not experience slowing of the progression of their disease, according to two articles in The Archives of Ophthalmology, one of the JAMA/Archives journals.
Retinitis pigmentosa is a disorder of the light-collecting cells on the retina—the layer at the back of the eye that collects light—and can cause vision loss. According to the article, retinitis pigmentosa affects about one in 4,000 people worldwide. Previous studies have shown that patients treated with vitamin A have a slower decline in retinal function and vision loss compared to patients who do not take vitamin A. Other studies have found that patients with retinitis pigmentosa tend to have lower blood levels of docosahexaenoic acid (DHA), an omega-3 fatty acid found in the photoreceptor cells.
Eliot L. Berson, M.D., of the Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, and colleagues investigated whether giving oral DHA to patients already receiving vitamin A treatment could halt or slow the course of their retinitis pigmentosa.
The researchers studied 221 patients with retinitis pigmentosa aged 18 to 55 years who were followed over a four year period. Patients were given either 1,200 milligrams per day of DHA or control capsules (placebo), and all were given 15,000 IU/d (international units per day) of vitamin A.
The researchers write that “No significant differences in decline in ocular function were found between the docosahexaenoic acid plus vitamin A (DHA+A) group and control plus vitamin A (control + A) group over a four-year interval.”
“In patients assigned to receive 15,000 IU/d of vitamin A, this randomized trial showed that 1,200 milligrams per day of docosahexaenoic acid supplementation over a four-year interval did not, on average, slow the course of disease in patients with retinitis pigmentosa,” the researchers conclude.
In a separate analysis from the same study also reported in this issue of The Archives of Ophthalmology, Dr. Berson and colleagues investigated the effect of DHA and vitamin A treatment in the patients with retinitis pigmentosa according to whether or not patients were taking vitamin A before enrolling in the study.
Thirty percent of those patients were not taking vitamin A prior to entering the study.
The researchers found that “Among patients not taking vitamin A prior to entry, those in the DHA+A group [30 patients] had a slower decline in [vision loss] than those in the control +A group [35 patients] over the first two years; these differences were not observed in years three and four of follow-up or among patients taking vitamin A prior to entry.”
The researchers conclude: “For patients with retinitis pigmentosa beginning vitamin A therapy, addition of docosahexaenoic acid, 1,200 milligrams per day, slowed the course of disease for two years. Among patients on vitamin A for at least two years, a diet rich in omega-3 fatty acids (0.20 grams per day or more) slowed the decline in [vision loss].”
“The present study also supports a previous recommendation that most adults with the typical forms of retinitis pigmentosa should continue to take 15,000 IU/d of vitamin A palmitate under medical supervision to slow the course of their condition,” the authors write. “It should be noted that the precursor of vitamin A, betacarotene, is not predictably converted into vitamin A; therefore, betacarotene is not a suitable substitute for vitamin A palmitate in the context of this treatment regimen.”