Low Vitamin D Linked to Vision Loss from AMD

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Researchers found women with the highest levels of 25-OH-D actually had a significantly reduced risk of developing AMD compared with women with low levels.

Dr. Amy Millen at the University of Buffalo reported results from a study, which examined data from 968 postmenopausal women from the Women?s Health Initiative Study under the age of 75 to determine if age-related macular degeneration (AMD) was related to their vitamin D status. The level of 25-OH-D in the serum is considered to be the best biomarker for vitamin D status as it reflects not only dietary intake of vitamin D but also the amount of vitamin D produced in the skin from exposure to ultraviolet rays from the sun. Given that increased sun light exposure is believed to directly damage the retina and contribute to the development of AMD one might suspect that women with higher levels of 25-OH-D might also have an increased risk of AMD. However, the data showed no significant correlation between reported sun exposure and AMD. Indeed, the researchers found women with the highest levels of 25-OH-D actually had a significantly reduced risk of developing AMD compared with women with low levels. Given the known harmful effects of ultraviolet radiation in promoting AMD this result is a bit perplexing although it is consistent with one earlier study that found AMD was associated with poorer vitamin D status. Dr. Millen?s data did show that increased vitamin D from dietary sources was associated with a reduced risk of developing early AMD.1

AMD afflicts about 8.5 million Americans and is the #1 cause of irreversible vision loss in the United States and other developed countries. AMD shares many of the same risk factors as cardiovascular disease (CVD) including high-fat diets, smoking, obesity & type 2 diabetes, hypertension, high red meat intake, and low intake of fruits and vegetables. In addition, low levels of 25-OH-D in the serum have been repeatedly to an increased risk of CVD. However, the recent panel of experts who set the most recent RDA for vitamin believed the data from these observational studies linking lower vitamin D status to CVD was insufficient and might be due to reverse causation. Healthy active people would have higher 25-OH-D and less CVD but not because of the increased vitamin D but because they spent more time outdoors and had more sunlight exposure. Clearly, this reverse causation hypothesis cannot also explain why higher levels of 25-OH-D appear to reduce the risk of developing AMD as more ultraviolet light exposure increases the risk of AMD.

By J. Kenney, PhD, RD, FACN

Reference:

1. Arch Opthal 2011;129:481-9

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