June 20, 2017
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NHANES: Vitamin D deficiency may worsen retinopathy in well-controlled type 2 diabetes

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Middle-aged adults with well-controlled type 2 diabetes and vitamin D deficiency may be more likely to develop mild or severe diabetic retinopathy when compared with adults who have well-controlled diabetes without vitamin D deficiency, according to an analysis of National Health and Nutrition Examination Survey data.

Vitamin D deficiency is common worldwide, and studies indicate the overall prevalence rate of vitamin D deficiency in U.S. adults was 41.6%,” Min Long, MD, of the department of endocrinology and metabolism at the Second Affiliated Hospital of Chongqing Medical University in China, and colleagues wrote. “Vitamin D deficiency has been implicated and may have a role in development and severity of diabetic retinopathy. However, study results have been inconsistent with respect to the association of vitamin D and diabetic retinopathy, and the reasons for [the] differences in study finding are unclear.”

Long and colleagues analyzed data from 842 adults aged at least 40 years with diabetes, participating in the 2005-2008 waves of NHANES (mean age, 61 years; 52.8% women). Researchers assessed retinopathy severity, HbA1c, socioeconomic status and behavioral parameters, including smoking status and vitamin D intake, as well as diabetes duration and serum 25-hyrdoxyvitamin D and lipid profiles. Researchers used ordinal regression analysis to determine factors associated with retinopathy severity.

Within the cohort, 301 participants (35.7%) had diabetic retinopathy; 195 (23.2%) had mild nonproliferative retinopathy, and 106 (12.6%) had severe nonproliferative or proliferative retinopathy.

Researchers found that participants with severe nonproliferative or proliferative retinopathy had the longest duration of diabetes (mean duration, 18.2 years), followed by those with mild nonproliferative retinopathy (mean duration, 14.4 years) vs. those with no retinopathy (mean duration, 7.5 years). Those with severe nonproliferative or proliferative retinopathy were also more likely to have poorly controlled hyperglycemia vs. those with mild nonproliferative retinopathy or no retinopathy (71.6% vs. 65.3% and 33.1%, respectively).

In multivariable regression analysis, researchers found that male sex (OR = 1.602; P = .001), increased diabetes duration (OR = 1.072; P < .001) and poorly controlled hyperglycemia (OR = 3.522; P < .001) were associated with greater retinopathy severity.

In examining vitamin D deficiency status and its association with retinopathy, researchers observed no between-group differences in retinopathy severity in patients with and without vitamin D deficiency with poorly controlled hyperglycemia. However, among participants with well-controlled glucose levels, incidence of severe retinopathy was more likely in those who had vitamin D deficiency vs. those who had sufficient vitamin D status (8.5% vs. 5.3%), as was incidence of mild retinopathy (17.3% vs. 13.4%). Researchers also observed an interaction of HbA1c with vitamin D deficiency (P = .038); results persisted after adjusting for sex, race and duration of diabetes.

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“Our results indicate insufficient vitamin D may increase the risk of severe diabetic retinopathy only in patients with well-controlled glycemia,” the researchers wrote. “Subgroup analysis that examined the severity of retinopathy in patients with poorly controlled or well-controlled glycemia with and without vitamin D deficiency found that vitamin D deficiency and dichotomous HbA1c have significant interaction, and greater [nonproliferative] severity was associated with vitamin D deficiency for both glycemia populations. The fact that the risk factors in our study differed between the well-controlled and poorly controlled glycemic subgroups strongly suggests that future studies should consider this issue within their study design.” – by Regina Schaffer

Disclosures: The researchers report no relevant financial disclosures.