Background/Purpose:

Vitamin D deficiency is highly prevalent in patients with rheumatoid arthritis (RA), and it is linked to RA disease severity. Two steps of hydroxylation are required to activate vitamin-D, the first is carried out in the liver to be converted to 25-vitamin-D and then in the kidney to 1,25 vitamin-D; the active form. Subclinical kidney dysfunction is common in rheumatoid arthritis and might interfere with vitamin-D hydroxylation. This study investigates the relationship between vitamin-D level and kidney function in RA

Methods:

Patient diagnosed by ACR 1988 criteria for RA. 25-viamin D level was obtained. Estimated glomerular filtration rate (eGFR) calculated with Modification of Diet in Renal Disease (MDRD) formula. Univariate regression analysis was carried out to determine the relationship between 25-vitamin-D level and eGFR, other renal parameters, and the inflammatory markers

Results:

55 rheumatoid arthritis patients were included for the study. The mean age was 45 ± 15 year for female and 46 ± 21 year for male. The mean 25-vitamin-D level was 39 ± 28 nmol/l (normal range: 50-80). Mean eGFR was 130 ±25 ml/min/m^2..

Univariate linear regression revealed a positive linear relationship between 25-vitamin-D level and weight of the patients (p=0.03, CI: 0.06, 1.04), body surface area (p=0.02, CI: 11-119), body mass index (BMI) (p=0.009, CI: 0.60, 4.00), and calcium level (p=0.02, CI: 7.25, 130). 25-vitamin-D level was negatively associated with eGFR (p=0.040, CI: -0.20, -0.01), microalbuminuria level (p=0.040, CI: -0.63, -0.01), CRP level (P=0.01, CI: -1.16, -0.16) and neutrophil count (p=p=0.03, CI: -1.67, -0.010).

Conclusion:

The negative linear relationship between 25-vitamin D level and the eGFR indicates high level of 25-vitamin-D due to kidney inefficiency in converting 25-vitamin-D to an active form; 1, 25 vitamin-D. Extrarenal activation of vitamin D require a high level of 25-vitamin-D of more than 78 nmol/l (30 ng/ml) for sufficient activation. Vitamin-D receptors are present in most cells in the body and in the T and B lymphocytes. The active form of vitamin-D (1, 25 vitamin-D) is one of the most potent modulator of the immune system. Hence, the negative relationship between 25-vitamin-D and CRP indicate 25-vitamin-D deficiency role in exacerbation of the inflammatory status, and possibly in a further renal function deterioration. Screening for 25-vitamin-D deficiency might be an important step to detect subclinical renal insufficiency. Vitamin-D supplement might help in ameliorating the inflammation of rheumatoid arthritis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/in-rheumatoid-arthritis-vitamin-d-deficiency-is-an-outcome-and-a-cause-of-subclinical-renal-impairment/