Age-related macular degeneration (AMD) is the leading cause of blindness and irreversible vision loss.
Several epidemiological studies have linked higher intakes of fish and omega-3s to reduced rates of AMD.
And four years ago, an analysis of data from the huge National Health and Nutrition Examination Survey found that Americans whose blood levels of vitamin D ranked in the top one-fifth were 36 percent less likely to develop “dry”, early stage AMD (Parekh N et al 2007).
And people who reported eating lots of fish enjoyed an even more dramatic 59 percent drop in the risk of “wet” (later-stage, blinding) AMD … presumably because of added eye support from the omega-3s in fish.
Now, a new analysis of data from participants in the Carotenoids in Age-Related Eye Disease Study (CAREDS) suggests that vitamin D may help prevent AMD.
Higher vitamin D levels linked to 44 percent lower eye risk
The new analysis found that women under the age of 75 with high vitamin D blood levels were less likely to have “early” AMD (Millen AE et al. 2011).
The results showed that women younger than 75, whose vitamin D levels were lower than 38 nanomoles per liter (nmol/L) were more likely to have AMD, compared with women whose blood levels were above that mark.
Specifically, women with a vitamin D blood level above 38 nmol/L were 44 percent less likely to have AMD.
This statistical correlation between higher D levels and lower risk does not prove that vitamin D prevents AMD, which only rigorous clinical trials can do.
According to lead author Amy E. Millen, Ph.D., “The take-home message from this study is that having very low vitamin D status [below 38 nanomoles per liter] may be associated with increasing your odds of developing age-related macular degeneration.”
But as she noted, “being at a higher vitamin D level than 38 nanomoles per liter does not appear to be more protective.”
Professor Millen said that people can increase their vitamin D levels by spending moderate amounts of time in sunlight, and eating foods rich in vitamin D, such as fatty fish, by taking supplements, and eating D-fortified cereals and dairy foods.
The research was funded by the National Institutes of Health (NIH) and by Research to Prevent Blindness.
How much D is enough?
Scientists and doctors can measure and express vitamin D levels either as nanomoles per liter (nmol/L) or nanograms per liter (ng/L).
The U.S. Institute of Medicine (IOM) considers vitamin D blood levels below 30 nmol/L deficient and a level below 50 nmol/L inadequate.
These nmol/L figures equate to 12 nanograms per liter (ng/mL) and 20 ng/mL, respectively.
Actually, the IMO says that levels below 30 nmol/L and 50 nmol/L these put people “at risk for” deficiency or inadequacy, respectively.
But as John Cannell, M.D., president of the Vitamin D Council says, it is misleading to say that blood levels below these put people “at risk for” deficiency or inadequacy, since these blood levels virtually define deficiency and inadequacy.
Most leading vitamin D researchers recommend much higher minimum blood levels ranging from 90 to 120 nmol/L (36 to 48 ng/mL), to ensure optimal health.
In November of 2010, the IOM's Food and Nutrition Board tripled the recommended daily allowance (RDA) for people from age one through 50, from 200 IUs to 600 IUs.
Unfortunately, the IOM panel retained its prior recommended minimum blood level of 20 ng/mL (i.e., 50 nmol/L), which is well above the 38 nmol/L now associated with a 44 percent lower risk of AMD.
In contrast, virtually all of the world's leading vitamin D researchers recommend a minimum blood level of 30 ng/mL (i.e., 75 nmol/L), because this much-higher-than-average level is associated with lower risk of major diseases.
For example, leading vitamin D researcher Michael F. Holick, M.D., Ph.D., of Boston University says the evidence supports keeping vitamin D levels above 30 ng/mL (75 nmol/L). And he notes that levels up to 100 ng/mL are safe for everyone except sarcoidosis patients.
Millen AE, Voland R, Sondel SA, Parekh N, Horst RL, Wallace RB, Hageman GS, Chappell R, Blodi BA, Klein ML, Gehrs KM, Sarto GE, Mares JA; for the CAREDS Study Group. Vitamin D Status and Early Age-Related Macular Degeneration in Postmenopausal Women. Arch Ophthalmol. 2011 Apr;129(4):481-489.
Parekh N, Chappell RJ, Millen AE, Albert DM, Mares JA. Association between vitamin D and age-related macular degeneration in the Third National Health and Nutrition Examination Survey, 1988 through 1994. Arch Ophthalmol. 2007 May;125(5):661-9.