Vitamin D's Role in Eye Health
By Leo Semes, OD, FAAO
In fashion circles it is said that orange is the new black. Linus Pauling popularized the beneficial antioxidant properties of vitamin C, which, unlike what the color orange is likely to do, have remained in vogue. The Oregon State University continues Pauling's legacy with an eponymous institute covering micronutrients (http://lpi.oregonstate.edu/). The section on vitamin C contains more than 120 references, mostly from the 21st century.
Is Vitamin D the New C?
What has emerged in recent years is the significance of vitamin D. Although strictly classified as a hormone, vitamin D3 (cholecalciferol) can be synthesized in the skin upon exposure to ultraviolet-B (UVB) radiation from sunlight, or it can be obtained from the diet. Dietary sources include salmon, mackerel, and sardines; fortified milk, orange juice, and cereal; and egg yolk. Deficiency of vitamin D has been linked to such diverse disorders as rickets, osteomalacia, and osteoporosis; colorectal, breast, and prostate cancer; several autoimmune diseases including diabetes mellitus, multiple sclerosis (MS), and rheumatoid arthritis; and systemic hypertension as well as muscle weakness and pain.
Rickets and its successful treatment through sunlight exposure led to the fortification of milk with vitamin D, but an outbreak of hypercalcemia linked to vitamin D in the 1950s in England resulted in regulations forbidding the fortification of dairy products with vitamin D throughout Europe (Holick, 2011).
Vitamin-D deficiency can be assessed through laboratory tests measuring 25-(OH) D level. While most of us will not be ordering or interpreting such test results, it is worth noting that most experts agree that a 25-(OH) D level of >30ng/mL is considered to represent sufficient vitamin D with variability according to age and sex (Holick, 2011).
The pendulum began swinging back toward sun exposure for vitamin-D deficiencies only recently, which has spurred research into vitamin D's role in a variety of diseases. A recent study on the role of vitamins A, D, and E among Sjögren's syndrome patients reported that the levels of only the antioxidant vitamins (A and E) were reduced in the Sjögren's patients compared to the controls (Szodoray et al, 2010).
A little closer to home is the potential positive effect of vitamin D at adequate levels in macular degeneration. The Carotenoids in Age-Related Eye Disease Study recently showed that serum vitamin-D levels were associated with a decreased risk of AMD. These positive associations applied to women under age 75. The study methods found the correlations for serum vitamin-D levels and dietary and supplement intake but not for reported sunlight exposure. The authors conclude that high serum vitamin-D levels may be protective against AMD in women younger than 75 years (Millen et al, 2011).
There may be a role for vitamin-D supplementation in patients who have MS. While this is likely beyond the scope of eye care, it is worthwhile knowledge for anyone encountering an MS patient. A small trial looked at 25 patients who received escalating doses of vitamin D over one year compared with 24 controls. Those in the intervention group had fewer replaces and improved Expanded Disability Status Scale scores (Burton et al, 2010).
If Supplementation is Needed
Vitamin-D supplementation may be obtained from multivitamin supplements, typically 400 IU (10mcg) daily. Single-ingredient vitamin D supplements may provide 400 to 2,000 IU. A number of calcium supplements may also provide vitamin D. Although adverse events are unlikely, serum vitamin-D levels should be monitored when administering supplements. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #190.
Dr. Semes is a professor of optometry at the UAB School of Optometry. He is also a consultant or advisor to Alcon, Allergan, Optovue, and Zeiss.