The findings come from a US study which shows that women with a high genetic risk of AMD and vitamin D deficiency are 6.7 times more likely to develop the condition than those without increased genetic risk or deficiency.
Researchers led by scientists at the State University of New York, Buffalo collected data from 1,230 women aged 54–74 as part of the Carotenoids in Age-Related Macular Degeneration Study (CAREDS). The women were recruited from the Women’s Health Initiative Observational Study, a major longitudinal study focusing on disability, disease and death in more than 160,000 postmenopausal women in the US.
Measures of a biomarker in the blood stream, calcifediol, were used to gauge vitamin D levels, and used genetic data to identify women with a specific variant of the CFH gene – mutations in which have been associated with an increased risk of AMD.
CFH encodes complement factor H (CFH), a protein involved in the immune response to destroy and remove foreign invaders such as bacteria and viruses. The researchers believe that the complement immune system may target drusen – the deposits of protein and lipid which accumulate in the eye, especially in early stage AMD – resulting in inflammation which drives AMD.
“Your body sees this drusen as a foreign substance and attacks it, in part via the complement cascade response,” said Amy E. Millen, lead author of the study and associate professor of epidemiology and environmental health at Buffalo. “We see more AMD in people who have certain variants in the [CFH] gene which encodes a form of this CFH protein that is associated with a more aggressive immune response.”
She added: “Our study suggests that being deficient for vitamin D may increase one's risk for AMD, and that this increased risk may be most profound in those with the highest genetic risk for this specific variant in the CFH protein.”
The findings are believed to be the first to implicate vitamin D levels in AMD and supplementation may not be the solution. While the risk of AMD was high in women with califediol levels below 12ng/mL, increasing levels beyond this failed to significantly lower the risk.
Dr Millen added: “Our message is not that achieving really high levels of vitamin D is good for the eye, but that having deficient vitamin D levels may be unhealthy for your eyes.”
The research is published in the journal JAMA Ophthalmology.