Nutrient Supplementation for RP

Retinitis pigmentosa (RP) refers to a group of inherited progressive retinal dystrophies characterized by photoreceptor degeneration. The rods are affected initially, followed by gradual death of the cones. It's estimated that 1 in 4,000-5,000 people have RP worldwide. Since no generally accepted medical or surgical treatment can stop the course of the disease, researchers have undertaken studies with various nutritional supplements in hopes of improving visual function or slowing disease progression. Along with vitamin A , DHA and an omega-3 rich diet, lutein has recently been reported to be of potential benefit in RP.

Lutein May Benefit Visual Field and Acuity

Spurred by previous studies suggesting lutein as a potential treatment with positive effects on macular pigment density, researchers from the Wilmer Eye Institute conducted a double-blind, randomized placebo-controlled trial with a cross-over design (1). Thirty-four adult RP patients were randomized to 2 groups and followed for 48 weeks. One group received lutein supplements (10 mg/day for 12 weeks followed by 30 mg/day) for the first 24 weeks, then placebo for the following 24 weeks. The second group received placebo prior to lutein. Both groups were given a multi-vitamin and mineral supplement.

Lutein supplementation had a significant effect on central visual field. Visual acuity also improved slightly, though no effect on contrast sensitivity was observed. Comparing the development of vision measures against the natural loss expected to occur over 48 weeks, most measures showed reduced decline. These reductions were significant for normal illumination visual acuity and contrast sensitivity. The results, according to the authors, suggest that lutein supplementation improves visual field and may also modestly improve visual acuity.

Vitamin A Helps Preserve Visual Function

In 1993, Harvard investigators reported that 15,000 IU of vitamin A palmitate slowed the rate of decline of retinal function over 5 years as measured by ERG (2). In this study of 600 RP patients, high dose vitamin A helped preserve retinal function, while those getting high dose vitamin E (400 IU) were more likely to show a functional decline. A later study following adult RP patients taking high dose vitamin A for about 12 years concluded that prolonged intake is considered safe in this age group (3), although routine monitoring of liver function and fasting serum vitamin A levels are advised. Women of childbearing age should not take high dose vitamin A, which may raise the risk of birth defects.

Antioxidants Protect Cones in Animal Model

Why the negative affect of high dose vitamin E on RP function? It is possible that high dose vitamin E might have inhibited the absorption or transport of vitamin A, since patients receiving high doses had slight but significant decreases in serum A levels compared with those receiving lower doses in the 1993 Harvard study.

However, further exploratory studies of combined antioxidants in RP patients may be warranted. A recent study in an animal model of RP found that high dose antioxidants (vitamins E, C, alpha lipoic acid others) significantly reduced oxidative damage in cones, increased cone cell density and preserved cone function. These results, according to the Johns Hopkins authors, suggest that the gradual cone death that occurs after rod cells die is due to oxidative damage, and that antioxidants could provide benefit (4).

Omega-3 Fatty Acids Support Visual Field

While a 4 year long study published in 2004 reported that 1,200 mg of supplemental DHA along with high dose vitamin A did not slow the course of RP overall, further subgroup analysis showed benefit for those starting vitamin A supplementation for the first time (5,6). In addition, those study participants taking vitamin A (but not DHA) who also had a higher dietary omega-3 intake experienced substantial benefit. The rate of visual field decline was retarded by 40-50% yearly in those whose omega-3 intakes were equivalent to 1-2 servings of fatty fish weekly.

References

1. Bahrami H, et al. Lutein supplementation in retinitis pigmentosa: PC-based vision assessment in a randomized double-masked placebo-controlled clinical trial. BMC Ophthalmology 6:23, 2006.
2. Berson EL, et al. A randomized trial of vitamin A and vitamin E supplementation for retinitis pigmentosa. Arch Ophthalmol 111:761-72, 1993.
3. Sibulesky L, et al. Safety of <7500 RE (<25,000 IU) vitamin A daily in adults with retinitis pigmentosa. Am J Clin Nutr 69:656-63, 1999.
4. Komeima K, et al. Antioxidants reduce cone cell death in a model of retinitis pigmentosa. PNAS 103:1130-35, 2006.
5. Berson EL, et al. Clinical trial of docosahexaenoic acid in patients with retinitis pigmentosa receiving vitamin A treatment. Arch Ophthalmol 122:1297-305, 2004.
6. Berson EL, et al. Further evaluation of docosahexaenoic acid in patients with retinitis pigmentosa. Arch Ophthalmol 12:1306-14, 2004.