The Eyes Have It

Diet is vital to preservation of vision as we age. Some people have a higher risk of losing central vision than others—based partly on genetics—but that can be postponed or prevented by consuming sufficient levels of certain dietary nutrients. Clinicians are advised to provide dietary counsel especially to young persons who are susceptible to the vision-disabling consequences that accompany the genetic variations responsible for early onset of age-related macular degeneration (AMD). That gene is officially termed “complement factor H,” abbreviated to CFH. Researchers in the Netherlands tested more than two thousand individuals over age 55 for genetic susceptibility to AMD by way of the CFH gene. The subjects were followed for more than a decade, receiving eye exams every three years to learn who suffered from vision deterioration or loss. Careful, detailed dietary intake records were kept, and eating habits were monitored. The risk reduction ascribed to specific nutrients was associated with normal dietary intake.

Genetic variations can increase the risk of early age-related macular degeneration.  Using food frequency questionnaires and genetic testing, researchers at the Erasmus Medical Center in the Netherlands (Ho and van Leeuwen. 2011) evaluated biological interactions among risk factors for ARM, and found distinct relationships “…between CFH Y402H and zinc, beta-carotene, lutein/zeaxanthin, and eicosapentaenoic/docosahexaenoic acid (EPA/DHA)…”  Subjects with dietary intake of zinc in the highest third “…reduced their hazard ratio of early AMD…” by more than 40%.  Intakes of beta-carotene, lutein/zeaxanthin, and EPA/DHA reduced risk by more than a third.  Drs. Ho and van Leeuwen concluded their report with,”High dietary intake of nutrients with antioxidant properties reduces the risk of early AMD in those at high genetic risk.”

COMMENTARY AMD is a disease that affects the macula, the most important part of the retina and an area that has a very high concentration of photoreceptors, responsible for central vision.  Nerve fibers in the macula coalesce with neighboring fibers to form the optic nerve, the “cable” that connects the eye to the brain.  The health of our eyes depends on the health of the cardiovascular and nervous systems.  The retina and surrounding structures are filled with blood vessels that depend on a healthy cardiovascular system.

The link between vision and diet has been recognized for a considerable time.  In 2006, a study funded by the Agricultural Research Service and reported in the American Journal of Clinical Nutrition  found a relationship between a high glycemic-index (GI) diet and AMD.  The glycemic index is a ranking of foods based on their elevation of blood glucose after ingestion, compared to a reference food such as white bread or glucose.  These scientists suggested a direct relationship of glycemic index to eye disease.  Study participants whose diets contained the highest GI foods also had the highest amount of macular pigment abnormalities, which is an early indicator of macular degeneration.  (Chiu. 2006)  It seems prudent, therefore, to limit or completely avoid foods that are high in starches and sugars, particularly sugars that are added, as found in processed foods, sweets, and the like.

Addressing the nutrients mentioned in the Ho and van Leeuwen study, zinc is already a necessary trace mineral, in that it is a component of several enzymes and brings vitamin A from the liver to the retina in order to produce melanin, a protective pigment of the eye.  Zinc is heavily concentrated in the eye, mostly in the retina and the choroid, the vascular tissue beneath the retina.  Food sources include red meats, beans, nuts (almonds), whole grains, shellfish (oysters), and fortified foods.

Lutein and zeaxanthin are nutrients found in green leafy vegetables and eggs, as well as in other foods.  There’s more reason to eat your spinach than merely to be like Popeye. These two compounds have identical chemical formulas, and are thus called isomers of each other. (The arrangement of atoms is slightly different.)  Many studies have related these substances to the prevention of AMD as well as cataracts.  Of all the carotenoids found in nature, these are in the greatest amounts in the eye, where they absorb the blue light that can cause oxidative damage.  They have to come from food, so we advise that you get the darkest greens you can find, including spinach, kale, collards, and turnip greens.  Squash, pumpkin, corn, Brussels sprouts, peas, carrots, and green beans are other vegetable sources.  The fruits include citrus.

Lack of vitamin A may cause might blindness, dry eyes, eye infections, skin problems and slowed growth.  Beta-carotene is a compound that can be converted by the body to vitamin A.  The need for vitamin A in vision was identified almost a hundred years ago.  Foods that contain beta-carotene or vitamin A include dark green leaves, and the yellow-orange groups, such as cantaloupe, pumpkin, yellow squashes, and others.  In the eye, beta-carotene becomes retinaldehyde, also called retinal, and is bound to a protein called opsin, which resides in the rods and cones.  This combination helps to carry electrical energy along the optic nerve to the brain.  Night blindness, by the way, is actually poor adaptation to low-light situations.

The essential fatty acids, in this case EPA and DHA, must come from the diet.  They maintain integrity of the nervous system, and help to prevent inflammation and arteriosclerosis, a noted enemy of vision.  One result of arteriosclerosis is a decrease in nutrients to the eye and a reduction in the removal of waste materials.  EPA and DHA also aid in the reduction of dry eyes.  It is well-known that oily fish are the best food sources of these essential fats, though supplements are available.

Oh, yeah.  You never see a rabbit wearing glasses.  Eat your carrots.

MAIN ABSTRACT Arch Ophthalmol. June 2011;129(6):758-766. Reducing the Genetic Risk of Age-Related Macular Degeneration With Dietary Antioxidants, Zinc, and {omega}-3 Fatty Acids The Rotterdam Study Lintje Ho, MD, MPH, MSc; Redmer van Leeuwen, MD, PhD; Jacqueline C. M. Witteman, PhD; Cornelia M. van Duijn, PhD; André G. Uitterlinden, PhD; Albert Hofman, MD, PhD; Paulus T. V. M. de Jong, MD, PhD, FRCOphth; Johannes R. Vingerling, MD, PhD; Caroline C. W. Klaver, MD, PhD

SUPPORTING ABSTRACTS Semin Ophthalmol. 2011 May;26(3):192-7. Inflammation and Age-Related Macular Degeneration (AMD). Telander DG. Department of Ophthalmology and Vision Science, University of California Davis Medical Center, Sacramento, CA, USA.

Arch Ophthalmol. 2007 Mar;125(3):300-5. High-sensitivity C-reactive protein, other markers of inflammation, and the incidence of macular degeneration in women. Schaumberg DA, Christen WG, Buring JE, Glynn RJ, Rifai N, Ridker PM. Division of Preventive Medicine, 900 Commonwealth Ave E, Boston, MA 02215, USA. dschaumberg@rics.bwh.harvard.edu

American Journal of Clinical Nutrition, Vol. 83, No. 4, 880-886, April 2006 Dietary glycemic index and carbohydrate in relation to early age-related macular degeneration Chung-Jung Chiu, Larry D Hubbard, Jane Armstrong, Gail Rogers, Paul F Jacques, Leo T Chylack, Jr, Susan E Hankinson, Walter C Willett and Allen Taylor

Pol Merkur Lekarski. 2011 Apr;30(178):241-5. .