The Association of Vitamin D With Estimated Glomerular Filtration Rate and Albuminuria: 5th Korean National Health and Nutritional Examination Survey 2011-2012.
OBJECTIVES
The kidney plays a key role in the metabolism of vitamin D. However, the relationship between GFR and 25(OH)D is not well understood. Moreover, few studies have investigated the effect of albuminuria, a known mediator of kidney function, on vitamin D levels. Our aim was to investigate the associations among estimated GFR (eGFR), albumin-creatinine ratio (ACR), and 25(OH)D.


METHODS
We investigated the relationship of 25-hydroxyvitamin D (25[OH]D) with eGFR and albuminuria in 11,336 adults who participated in the 5th Korea National Health and Nutrition Examination Survey (KNHANES) 2011-2012. The eGFR, ACR, and serum 25(OH)D were measured in participants who met the detailed inclusion criteria.


RESULTS
We found that after adjusting for covariates and log-ACR values, the mean (95% CI) eGFR decreased significantly with increasing 25(OH)D levels (Q1: 93.4 [92.7-94.0]; Q2: 91.9 [91.2-92.5]; Q3: 90.9 [90.3-91.6]; and Q4: 90.2 [89.5-90.8] mL/min/1.73m2; P < .001). However, the mean 25(OH)D value was highest at eGFR 61-90 mL/min per 1.73 m2 and decreased significantly with decreasing eGFR levels (>90: 17.3 [17.1-17.5]; 61-90: 17.6 [17.4-17.8]; 46-60: 17.1 [16.2-18.0]; 31-45: 16.2 [14.2-18.2]; ≤30: 13.8 [17.0-10.7] ng/mL; P = .008). After adjusting for covariates and log-eGFR, the mean ACR decreased significantly with increasing 25(OH)D quartiles (Q1: 22.0 [18.1-25.9]; Q2: 20.4 [16.6-24.2]; Q3: 16.3 [12.5-20.0]; Q4: 15.0 [11.2-18.8] μg/mg; P = .043).


CONCLUSIONS
The mean eGFR values were negatively associated with 25(OH)D levels independently of ACR. However, the mean 25(OH)D values were decreased significantly with decreasing eGFR levels in moderate and severe chronic kidney disease stages. Also, the mean ACR values were negatively associated with 25(OH)D levels independently of eGFR in an Korean adult population.