Seafood Omega-3s and High-Dose Vitamin A Slow Visual Loss in Retinitis Pigmentosa
The retina is a light-sensitive tissue lining the inner surface of the eye. Its specialized photoreceptor cells respond to incoming light by initiating a chain of reactions that trigger nerve impulses to the brain. The photoreceptors consist of two types of cells, rods and cones. The rods are responsible for night vision and when these cells are impaired, night vision dims. Individuals with the gene-based disease retinitis pigmentosa (Illustration) develop poor night vision that progresses to impaired peripheral vision (tunnel vision) and then loss of central vision. Some drug treatments are available to assist patients with this condition, but the most widely used therapies now include nutrients: vitamin A in high doses and long-chain omega-3 fatty acids (omega-3s) found in fish and shellfish. Vitamin A in large amounts used to be a worry because of its potential for liver damage, but its use in patients with retinitis pigmentosa has helped slow the loss in peripheral vision without detrimental effects and is now recommended. Eye specialists also wondered whether long-chain omega-3s would be advantageous in individuals with this disease. DHA, one of the main long-chain omega-3s, concentrates in the retina during fetal and infant development and is essential for optimum visual performance. There is some evidence that DHA levels in red blood cells are lower in patients with retinitis pigmentosa. Patients who consume higher amounts of seafood omega-3s (mainly DHA) appear to have a slower rate of visual decline. Most of these studies have involved a limited number of patients, which makes it difficult to obtain statistically significant results. To address the numbers problem, an experienced research group analyzed the combined the data from three of its studies. The consumption of long-chain omega-3s was estimated from dietary questionnaires and all participants had been consuming high-dose vitamin A for at least 4 years. Patients were screened annually for distance and retinal visual acuity and the rate of visual decline was calculated on annual basis. The participants formed two groups according to whether their omega-3 intake was above or below 200 mg per day on average. Those consuming 200 mg per day or more were considered “high” omega-3 consumers. The data analysis revealed that those patients who consumed 200 mg of omega-3s per day and high-dose vitamin A experienced a 40% slower decline in vision per year compared with those who ate less than 200 mg of omega-3s per day. From a practical point of view, this slowing in visual loss has huge implications. As the authors described it, consuming high-dose vitamin A plus at least 200 mg per day of seafood omega-3s would “make it possible for many patients with typical retinitis pigmentosa to retain both visual acuity and central visual field for most of their lives.” That’s foresight!