Dry eye is a common disease. Many patients continue to experience residual symptoms despite optimal treatment. Thus, new treatment options are required. The purpose of this study was to evaluate the association between serum 25-hydroxyvitamin D [25(OH)D] levels and dry eye.
This study was performed using data from the fifth Korean National Health and Nutrition Examination Survey, which is a cross-sectional study of the Korean population that was conducted from 2010 to 2011. We included adults aged >19 years who underwent ophthalmologic interviews and examinations. We excluded subjects who had comorbid conditions (rheumatoid arthritis, thyroid disease, chronic kidney disease, or depression) that are associated with dry eye. The subjects were divided into normal and dry eye groups. The dry eye group consisted of those who had clinically diagnosed dry eye syndrome or symptoms. Multiple logistic regression analysis was conducted to determine the association between serum 25(OH)D levels and dry eye.
In the univariate model, the 25(OH)D levels were lower in the dry eye group than in the normal group (P=0.01). A significant association was found between severe vitamin D deficiency (<10 ng/mL) and dry eye (P=0.04). However, after multivariate adjustment, the statistical significance of the association disappeared (P-values= 0.49, vitamin D insufficiency; P=0.33, vitamin D deficiency; P=0.18, severe vitamin D deficiency).
Severe vitamin D deficiency was associated with dry eye in an unadjusted model, but the association was not statistically significant after adjustment.
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The glomerular filtration rate (GFR) decreases with age, while parathyroid hormone (PTH) increases. There are a few reports only on the relationship between GFR and PTH under the category of serum 25-hydroxyvitamin D (25[OH]D) concentration.
Using the Korea National Health and Nutrition Examination Survey (KNHANES) data, a cross-sectional study was conducted on the association between serum 25(OH)D concentration, GFR and PTH in Korean adults aged 50 years or older. Serum PTH concentration was compared to the tertiles of GFR after adjustment for relevant variables. In addition, the serum PTH concentration was compared with the GFR under the category of serum 25(OH) D concentration (<20, 20-30, >30 ng/mL).
The mean estimated GFR (eGFR) was 74.8 mL/min in men and 73.1 mL/min in women. The mean PTH and 25(OH) D was 66.8 pg/mL, 20.5 ng/mL in men and 69.0 pg/mL, 18.2 ng/mL in women. The serum PTH concentration showed a significant negative correlation with the serum 25(OH) D and eGFR in both genders. The serum PTH concentration significantly increased at the lower tertile of eGFR in male adults In addition, a decrease of serum PTH concentration was marked in the vitamin D sufficient male adults (>30 ng/mL).
This present study demonstrated that serum PTH concentration showed negative correlation with eGFR, however, serum PTH increase may be minimized by maintaining proper serum 25(OH)D concentrations under similar eGFR status in Korean adults aged 50 and above.
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