Saturday, 30 October 2010
Vitamin D deficiency and Diabetic Retinopathy
Vitamin D Has Retinopathy Link
By John Gever, Senior Editor, MedPage Today
Published: October 20, 2010
Reviewed by Zalman S. Agus, MD; Emeritus Professor
University of Pennsylvania School of Medicine and
Dorothy Caputo, MA, RN, BC-ADM, CDE, Nurse Planner
* Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.
* Note that the study cannot determine causality, and that whether vitamin D supplementation can reduce the risk of diabetic complications is not known.
CHICAGO -- Diabetic retinopathy may be added to the list of conditions potentially related to vitamin D insufficiency, a researcher said here.
A study of 123 diabetic individuals with varying degrees of retinopathy, along with two groups of controls, showed that low vitamin D levels were significantly more common in those with the diabetic complication, according to John F. Payne, MD, of Emory University in Atlanta.
In a poster presentation here at the American Academy of Ophthalmology's annual meeting, Payne also reported that multivitamin use appeared to be helpful in preventing vitamin D insufficiency -- at least as currently defined.
"If you were taking a daily multivitamin, your mean vitamin D [25-hydroxyvitamin D] was about 31 [ng/mL] versus about 22 if you weren't taking a multivitamin," he told MedPage Today. Because 30 ng/mL was the cutoff Payne and colleagues had used to define insufficiency, "now you're up to the optimum level."
But he acknowledged that some researchers have begun to advocate for higher levels of daily vitamin D intake and serum levels of the 25-OH-D metabolite, relative to current norms, as necessary for health.
Payne and colleagues gathered a total of 221 individuals in five groups: 47 volunteers without diabetes or any eye disease; 51 without diabetes who had uveitis, macular degeneration, or other ocular diseases; 41 diabetics without eye disease; 40 diabetics with nonproliferative diabetic retinopathy; and 42 diabetics with proliferative disease.
Serum 25-OH-D levels were measured from December 2009 to March 2010, which eliminated seasonal effects on vitamin D levels.
Mean levels in the five groups were as follows (P<0.001 for diabetics versus nondiabetics):
* Healthy controls: 28.8 ng/mL
* Nondiabetics with eye disease: 24.7 ng/mL
* Diabetics without eye disease: 23.2 ng/mL
* Diabetics with nonproliferative retinopathy: 21.5 ng/mL
* Diabetics with proliferative retinopathy: 18.0 ng/mL
Vitamin D insufficiency was found in 81% of the proliferative retinopathy group and about 70% of the two other diabetic groups, versus 55% of the two nondiabetic groups (P=0.048).
Black participants, who made up about half the overall sample, had lower mean 25-OH-D levels than whites, at 23.7 versus 29.2 ng/mL -- a difference found in most studies, as melanin in the skin interferes with the vitamin D-boosting effect of sunlight.
But in multivariate analysis, which accounted for body mass index, glycated hemoglobin levels, and two measures of renal function, only the presence or absence of self-reported daily multivitamin use was significantly associated with 25-OH-D level (mean 31.1 versus 22.0 ng/mL).
Vitamin D insufficiency was seen in 44% of those taking daily multivitamins, versus 83% of those not taking them (P<0.001).
Payne said the big unanswered question remains whether vitamin D supplementation can reduce the risk of diabetic complications, or any of the wide range diseases that have been linked to vitamin insufficiency in previous studies. These have included breast cancer, heart failure, multiple sclerosis, GI infections, and age-related cognitive decline, among others.
He noted that in this cohort, there was not a significant relationship between reported multivitamin use and the presence or severity of diabetic retinopathy.
Payne added that a randomized, placebo-controlled trial of supplements might be impossible because withholding them from patients known to have vitamin insufficiency could be considered unethical.
"We may have to go about getting that data a bit differently than we normally would," he said.
Nevertheless, Payne recommended that patients and physicians should consider vitamin D supplements in the meantime, since they are safe and could very well be helpful.
The study was supported by Research to Prevent Blindness and the National Eye Institute.
Payne and colleagues declared they had no competing financial interests.
Primary source: American Academy of Ophthalmology
Payne J, et al "Vitamin D insufficiency in diabetic retinopathy" AAO 2010; Abstract PO223