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Wednesday, 02 September 2015
Vitamin D has been studied extensively in relation to bone health as well as cancer. Now, a team led by a researcher at the University at Buffalo (UB) has discovered that vitamin D may play a significant role in eye health, specifically in the possible prevention of age-related macular degeneration, or AMD, among women who are more genetically prone to developing the sight-damaging disease.
In a paper published in JAMA Ophthalmology online, Amy Millen, associate professor of epidemiology and environmental health in UB's School of Public Health and Health Professions, and her team found that women who are deficient in vitamin D and have a specific high-risk genotype are 6.7 times more likely to develop AMD than women with sufficient vitamin D status and no high risk genotype.
Macular degeneration is characterized by the deterioration of the macula, a small part of the central retina where the eye's photoreceptors (rods and cones) are most highly concentrated. The leading cause of legal blindness, macular degeneration affects more than 10 million Americans -- more than cataracts and glaucoma combined -- according to the American Macular Degeneration Foundation. If the same ratio relative to overall population were to apply to Ireland, we would have close to 120,000 people affected by AMD. The disease affects a person's central vision, which is needed for common tasks such as reading and driving. The effect is similar to that of a rain drop on the centre of a camera lens.
Researchers analysed data compiled on 1,230 women ages 54 to 74 who participated in the Carotenoids in Age-related Eye Disease Study (CAREDS), which is an ancillary study of the Women's Health Initiative (WHI) Observational Study (OS). The WHI OS is a major US National Institutes of Health-funded research program aimed at addressing the most common causes of death, disability and poor quality of life in postmenopausal women. UB is one of 40 WHI centres nationally. CAREDS was conducted among participants at three of the centres: University of Wisconsin (Madison), the University of Iowa (Iowa City) and the Kaiser Centre for Health Research (Portland, Oregon).
Researchers were able to determine participants' vitamin D status by analysing serum samples for a vitamin D biomarker, 25-hydroxyvitamin D [25(OH)D], which provided a glimpse into vitamin D intake through all sources: diet, supplements and sunlight.
Human skin can synthesize vitamin D when exposed to ultraviolet light, Millen explains. However, for many people, 15 to 30 minutes a day with 10 percent of their skin exposed might be sufficient. In winter months, when there is a lower solar angle, sun exposure may not be not sufficient to maintain blood level for people who live northern countries such as Ireland. At these times and locations, dietary intake may be needed. Dietary sources of vitamin D include fortified foods such as milk and foods that naturally contain vitamin D such as fatty fish like salmon and mackerel.
Researchers say, in addition to environmental factors, macular degeneration has been found to be strongly associated with genetic risk. Inflammation is believed to be involved in the development of macular degeneration.
Vitamin D shows promise for protecting against macular degeneration because of its anti-inflammatory and antiangiogenic properties; antiangiogenic refers to slowing the growth of new blood vessels, often seen in late stages of AMD.
This study supports a role for vitamin D in eye health. That's significant because when the Institute of Medicine's report on the dietary reference intakes for vitamin D and calcium were released in 2011, the committee could only make conclusions about D related to bone health, say the study authors. There wasn't enough evidence at that time to make any recommendation based on D status and other outcomes beyond bone health.
Source: JAMA Ophthalmology, 2015