The impact of over-the-counter vitamin D supplements on vitamin D and parathyroid hormone levels in chronic kidney disease.

BACKGROUND

In addition to the known disturbances in mineral metabolism and vitamin D activation, the majority of patients with chronic kidney disease (CKD) do not have sufficient vitamin D stores. The impact of supplementation with low-dose, nonactive forms of vitamin D (calciferol) on parathyroid hormone (PTH) levels in this population is unknown, however.

METHODS

A cross-sectional evaluation of vitamin D levels, intact parathyroid hormone (iPTH) and other laboratory results in 108 stage 3 and stage 4 CKD patients according to their intake of over-the-counter vitamin D.

RESULTS

37 patients took 400 IU of vitamin D daily with supplemental calcium and 71 did not. Compared to subjects who did not take it, patients who were on the supplement had higher 25(OH)D (31 +/- 15 vs. 17 +/- 9) ng/ml, higher 1,25(OH)D (21 +/- 12 vs. 16 +/- 9) pg/ml, lower iPTH (75 +/- 48 vs. 144 +/- 100) pg/ml and were more likely to meet K-DOQI PTH guidelines. However, these subjects were more likely to have oversuppressed iPTH values. The groups did not differ with regard to demographics, glomerular filtration rate and calcium and phosphorus levels.

CONCLUSIONS

Vitamin D supplements may be a valuable tool in the prevention and treatment of hyperparathyroidism in patients with stages 3 and 4 CKD. CKD patients who have oversuppressed PTH need to be asked about their vitamin supplement intake.