Vitamin K acts as a coenzyme in the γ-carboxylation of vitamin K-dependent proteins, including coagulation factors, osteocalcin, matrix Gla protein (MGP), and the growth arrest-specific 6 (GAS6) protein. Osteocalcin is a key factor for bone matrix formation (Fusaro et al. 2012)  (full text). MGP is a local inhibitor of soft tissue calcification. GAS6 activity prevents the apoptosis of vascular smooth muscle cells (Fusaro et al. 2011) . Few data on vitamin K intake in chronic kidney disease patients (Cranenburg et al. 2011)  (full text) and no data in patients on a Mediterranean diet are available. We carried out a pilot study to evaluate vitamin K intake in hemodialysis (HD) patients.
In this multi-centre controlled observational study, data were collected from 91 patients aged >18 years on dialysis treatment (55 M, 36 F) for at least 12 months and from 85 age-matched control subjects with normal renal function (55 M, 30 F). Participants completed a food journal of seven consecutive days for the estimation of dietary intakes of macro- and micro-nutrients (minerals and vitamins).
HD patients had a median (Q1,Q3) age of 71 (52,76), median dialytic age of 93 months, mean BMI of 25.3±5.2 Kg/m2. Control group median (Q1,Q3) age was 69 (55,75) years (see Table 1). HD patients had a significantly lower intake of vitamin K1 compared to controls (see Table 2). We also evaluated and compared between HD patients and controls the intake of other fat soluble vitamins and of nutrients closely associated with bone and mineral disorders in CKD patients (see table 2). All were decreased in HD patients.
Haemodialysis patients had a significantly low intake in vitamin K1, which could contribute to increase the risk of bone fractures and vascular calcifications. Since the deficiency of vitamin K intake seems to be remarkable, dietary counselling to HD patients should also address the adequacy of vitamin K dietary intake and bioavailability. Whether diets with higher amounts of vitamin K1 or vitamin K supplementation can improve clinical outcomes in dialysis patients remains to be demonstrated.