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Study finds no causal association between vitamin D and AMD
Even so, people with vitamin D deficiency were 30% more likely to have neovascular AMD than people with adequate serum vitamin D levels.
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The hypothesis of a causal association between vitamin D and age-related macular edema cannot be substantiated, according to a study in Ophthalmology that evaluated the link between single nucleotide polymorphisms in the vitamin D pathway and early AMD, late AMD and neovascular AMD.
“Vitamin D is very important for bone health,” co-author Astrid E. Fletcher, PhD, a professor of epidemiology at the London School of Hygiene and Tropical Medicine in the United Kingdom, said. “The possibility that vitamin D provides benefits to a wide range of other conditions has been examined in many studies; however, the evidence remains largely unconvincing.”
Fletcher said few studies have investigated vitamin D and AMD. “We were therefore interested in looking at this relationship in the European Eye Study, which is a population-based study of older people in seven different countries in Europe. We know that in Europe, where food is not fortified with vitamin D as it is in the U.S. and use of supplements is low, vitamin D deficiency is quite high, especially in the older population.”
The study involved 4,753 participants, “recruited in diverse settings, from the southern Mediterranean to the northern Baltic, covering a wide range of diets and sunlight exposure,” Fletcher said. “Sunlight is the main source of vitamin D.”
Nearly all participants, 4,496 of them, with a mean age of 73 years, provided a blood sample.
Among these subjects, 2,137 had no signs of AMD, 2,209 had early AMD, and 150 had late AMD, of whom 104 had neovascular AMD.
Mendelian randomization
The study evaluated the associations between serum vitamin D and genetic variants in vitamin D pathways with AMD.
“A variant is a single nucleotide polymorphism (SNP) in a specific gene,” Fletcher told Ocular Surgery News. “The genes we were interested in are those genes which play a role in vitamin D uptake and metabolism, of which seven genes have been identified. Studies have shown that the levels of vitamin D in the blood are influenced by these SNPs.”
This approach is known as Mendelian randomization. “Genetically inherited SNPs predispose an individual to lower or higher vitamin D levels over his or her lifetime,” Fletcher said. “If there is a relationship between these SNPs and AMD, this is strong evidence of a true effect of vitamin D on AMD.”
The study assessed 90 SNPs from seven genes, “more than in any other study on vitamin D and AMD,” Fletcher said.
Neovascular AMD
The investigators found no relationship between serum vitamin D and AMD or between vitamin D SNPs and early AMD. “However, for neovascular AMD, we found that people with serum vitamin D in the range indicating vitamin D deficiency were 30% more likely to have neovascular AMD compared to people with adequate serum vitamin D levels,” Fletcher said. “But there was no convincing evidence from the genetic results of an association with neovascular AMD.”
Fletcher said that she and her colleagues had an open mind about what their results might show. “We do not consider that any specific recommendation on vitamin D and AMD can be drawn from our study,” Fletcher said.
The authors also noted that residual confounding and reverse causation may explain the association of vitamin D deficiency and neovascular AMD.
“Many countries have national guidelines on vitamin D for health professionals and the general public, which are largely based on the essential role of vitamin D in bone health,” Fletcher said. “Patients with AMD tend to be in their seventh or eighth decade, so it is prudent to ensure their vitamin D levels are regularly checked by their family physician.” – by Bob Kronemyer
- Reference:
- McKay GJ, et al. Ophthalmology. 2016;doi:10.1016/j.ophtha.2016.09.007.
- For more information:
- Astrid E. Fletcher, PhD, can be reached at Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London WCIE 7HT, United Kingdom; email: astrid.fletcher@lshtm.ac.uk.
Disclosure: Fletcher reports no relevant financial disclosures.