A new study suggests that it is time for people to see the light—because high levels of vitamin D may reduce the risk of early stage age-related macular degeneration (AMD), the most common cause of blindness among older adults in the United States.
AMD occurs when the macula, located at the back of the retina and responsible for producing the sharpest vision, deteriorates over time. The condition currently affects more than 7 million individuals in the United States over 40 years old, with no known prevention methods.
The study, published in the May issue of Archives of Ophthalmology, analyzed data from 7,752 people who were part of the National Health and Nutrition Examination Survey. Intended to represent the entire U.S. population, study participants were enrolled between 1988 and 1994, given thorough physical examinations including blood and urine samples and photographs of the retinas and participated in interviews and questionnaires regarding sociodemographics, lifestyle habits and food intake. Of the participants, 11 percent had AMD.
Researchers split the participants’ data into five groups based on level of vitamin D in the blood and found that those in the highest group had a 40 percent lower risk of early AMD than those in the lowest group.
"Levels of serum vitamin D were inversely associated with early AMD but not advanced AMD," the authors say, adding that vitamin D may lower the risk of AMD by reducing inflammation or preventing the growth of new blood vessels in the retina, which contributes to some forms of the eye disease.
Vitamin D originally came into the limelight in 1920 as an important component of healthy bones, specifically discovered as a means to prevent rickets. Since then, the vitamin has been lauded for number of health benefits, including a role in cancer prevention. The body naturally produces vitamin D following exposure to sunlight and also can be ingested through fortified products like milk, soy milk and cereal grains.
In another AMD-related study, researchers found that eating fish rich in omega-3 fatty acids can also reduce the risk of the condition.
This study, also published in the Archives of Ophthalmology journal, ran from 1992 to 1998 and looked at 4,519 individuals aged 60 to 80 at the time of their enrollment. A food frequency questionnaire determined how often they consumed certain foods, such as fish with high levels of omega-3 fatty acids, and photographs were taken of the participants’ retinas to determine if they had AMD.
The 1,115 participants who did not show symptoms of AMD during this initial examination were then compared with those who did, including 658 individuals with symptoms of neovascular AMD, the most severe stage of the condition.
Researchers found that eating more than two medium (4-ounce) servings of fish per week was associated with the lowest risk for advanced AMD. Similar results were seen in regard to consumption of more than one serving of broiled or baked fish each week.
"Dietary total omega-3 long-chain polyunsaturated fatty acid intake was inversely associated with neovascular AMD,” the authors say, and also note a similar relationship in regard to DHA, a specific type of omega-3 fatty acid believed to affect the retina. "Higher fish consumption, both total and broiled/baked, was also inversely associated with neovascular AMD."
The authors say that the inverse relationship suggests fatty acids may influence the development of blood vessel and nerve-related retina diseases by forming compounds to promote cell survival and proper blood vessel function while reducing inflammation and maintaining energy balance.
Omega-3 fatty acids have long been thought to protect against coronary heart disease and some types of cancer. These acids are most commonly found in oily, cold-water fish like salmon, mackerel, herring, tuna, sardines and anchovies.
