According to findings published in the Archives of Ophthalmology, the highest average intakes of vitamin D from food and supplements (15.1 micrograms per day) were associated with a 59 percent decrease in the risk of developing early AMD, compared with the lowest average intakes (7.9 micrograms per day).
?This is the second study to present an association between AMD status and 25(OH)D, and our data support the previous observation that vitamin D status may potentially protect against development of AMD,? wrote the authors, led by Amy Millen, PhD, from the University at Buffalo, New York.
?More studies are needed to verify this association prospectively as well as to better understand the potential interaction between vitamin D status and genetic and lifestyle factors with respect to risk of early AMD,? they added.
As the name suggests, age-related macular degeneration (AMD) is a degenerative retinal disease that causes central vision loss and leaves only peripheral vision.
Despite the fact that approximately 25 to 30 million people worldwide are affected by AMD, awareness of the condition is low, says AMD Alliance International. And as Baby Boomers age, the Alliance expects incidence to be on the rise and triple by 2025.
The macula is a yellow spot of about five millimeters diameter on the retina. As we age, levels of the pigments in the macula decrease naturally, thereby increasing the risk of AMD. The yellow color is due to the content of the carotenoids lutein and zeaxanthin, which we derive from the diet.
Millen and her co-workers analyzed blood levels of vitamin D ? measured as 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form of the vitamin ? in 1,313 women aged between 50 and 79. ?Serum 25(OH)D is the preferred biomarker for vitamin D status, as it reflects vitamin D exposure from both oral sources and sunlight,? explained the researchers.
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. Both D3 and D2 precursors are transformed in the liver and kidneys into 25(OH)D, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body.
According to the study?s findings, the top food sources of vitamin D for the women were milk, fish, fortified margarine and fortified cereal.
Results showed that no overall relationship was found between vitamin D and any form of AMD, but when the researchers limited their analysis to women younger than 75, they found that higher 25(OH)D levels were associated with a significant decreased risk of early AMD.
?The inverse association between early AMD and 25(OH)D in women younger than 75 years was not explained by dietary intake of lutein plus zeaxanthin or polyunsaturated fat,? they added.
On the other hand, higher vitamin D levels were associated with a borderline statistically significant increased risk in women over 75.
Is it biologically plausible?
Commenting on the potential mechanism, Dr Millen and her co-workers note that inflammation is reported to be involved in the development of AMD, and that vitamin D has anti-inflammatory activity. As such the sunshine vitamin ?may suppress the cascade of destructive inflammation that occurs at the level of the retinal pigment epithelium?choroid interface in early stages of AMD?, they added.
The study was supported by the National Institutes of Health and by Research to Prevent Blindness. It was part of the Carotenoids and Age-Related Eye Disease Study, an ancillary study of the Women?s Health Initiative.
Source: Archives of Ophthalmology
2011, Volume 129, Number 4, Pages 481-489
?Vitamin D Status and Early Age-Related Macular Degeneration in Postmenopausal Women?
Authors: A.E. Millen, R. Voland, S.A. Sondel, N. Parekh, et al. for the CAREDS Study Group