Low vitamin B12 may increase the risk of age-related macular degeneration (AMD), a degenerative eye disease and common cause of vision decline after age 60. High vitamin D levels, meanwhile, may reduce the risk.
At the University of Sydney in Australia, researchers found that low blood levels of vitamin B12 were associated with an increased risk of AMD among more than 2,000 participants in the Blue Mountains Eye Study, a population-based assessment of visual impairment and common eye diseases among older Australians.
As well, high levels of homocysteine in the blood were associated with an increased likelihood of AMD in study participants over age 75. Homocysteine is an amino acid the body derives from the digestion of protein-rich foods.
"Increased homocysteine and low vitamin B12 were independently associated with an increased risk of AMD in this study population," the researchers concluded.
The possible role of vitamin D in protecting against AMD comes to light from the United States, where researchers scrutinized relevant data from the third National Health and Nutrition Examination Survey.
Individuals with higher levels of vitamin D were less likely to develop early AMD, the researchers found. Intake of milk and fish, both sources of vitamin D, seemed to reduce the risk; and vitamin D supplements seemed to help those who consumed little milk.
"This study provides evidence that vitamin D may protect against AMD," the researchers concluded, although acknowledging that more research is needed to confirm their findings.
Sources: Am J Ophthalmol. 2007 Feb;143(2):344-6. Epub 2006 Sep 29; Arch. Ophthalmol. 2007 May;125(5):661-9