Vitamin K supplementation and bone mineral density in dialysis: results of the double-blind, randomised, placebo-controlled RenaKvit trial.

BACKGROUND
Vitamin K deficiency is highly prevalent in patients on dialysis and may contribute to their low bone mineral density (BMD) and increased risk of fracture. This study investigated the effect of menaquinone-7 (MK-7) supplementation on BMD in patients on chronic dialysis.


METHODS
In a multicenter double-blind placebo-controlled intervention trial, 123 patients on chronic dialysis were randomised to a daily oral supplement of either MK-7 360 µg or placebo for 2 years. BMD of the distal radius (1/3, mid, ultra-distal, and total), femoral neck, lumbar spine (L1-L4), and whole body was assessed by Dual-energy X-ray Absorptiometry. Serum levels of vitamin K1 and MK-7, and plasma levels of total osteocalcin, dephosphorylated-uncarboxylated matrix Gla protein, and Protein Induced by Vitamin K Absence-II were measured to assess vitamin K status.


RESULTS
After 2 years, an accelerated BMD loss of the 1/3 distal radius was found with MK-7 supplementation (mean difference of changes relative to placebo -0.023 (95% CI (-0.039;-0.008)) g/cm2), whereas the decrease in lumbar spine BMD seen in the placebo group was prevented (mean difference of changes between groups 0.050 (95% CI (0.015;0.085)) g/cm2. No significant effects were observed at the remaining skeletal sites. Vitamin K status strongly improved in MK-7 supplemented participants.


CONCLUSION
Compared with placebo, an accelerated BMD loss of the 1/3 distal radius was found after 2 years of MK-7 supplementation, whereas a decline in lumbar spine BMD was prevented. As such, MK-7 supplementation might modify BMD site-specifically in patients on dialysis. In aggregate, our findings do not support MK-7 supplementation to preserve bone in patients on dialysis.