Studies have reported a low vitamin K status in chronic kidney disease patients in hemodialysis linked to an increased risk of atherosclerosis and increased bleeding tendency. The overall aim of this study is to investigate the underlying causes of the reported low vitamin K status and to improve the patients' vitamin K status through diet and supplement. The study is divided in 5 sub-trials listed below. Sub-trial 1-4 focuses on determining the underlying course of low vitamin K status while sub-trial 5 deals with possible solutions to the reported low vitamin K status.

The analysis method used to determine vitamin K status is dephosphorylated-uncarboxylated Matrix-Gla-Protein (dp-ucMGP). Dp-ucMGP is the inactive form of the protein MGP whose activation is vitamin K dependent. The dp-ucMGP analysis method is not a direct measure of vitamin K status. However, an increased concentration of dp-ucMGP is a manifestation of a low vitamin K status and vice versa.

Sub-trial 1: Intake of vitamin K Aim: To assess the patients' intake of vitamin K. Hypothesis: The daily intake of vitamin K is insufficient. Method: Patients are asked to fill out a food frequency questionnaire (FFQ). The FFQ is based on their intake of different foods rich in vitamin K during the last month. To compare the results from the FFQ with their actual vitamin K status a blood sample is collected and analyzed to determine dp-ucMGP. Participants: 30.

Sub-trial 2: The influence of dialysis Aim: To examine whether vitamin K status is compromised during dialysis. Hypothesis: Vitamin K is removed from the blood during dialysis. Method: A blood test is collected before and after dialysis and analyzed to determine dp-ucMGP. At the end of the dialysis a sample of the remaining dialysis-water is collected and analyzed to determine dp-ucMGP. Furthermore, the patients will be weighed before and after dialysis with the purpose of calculating concentrations. Participants: 16 (the analysis of the dialysis water is done for five patients at first, if the results are useful the analysis is done for every participant).

Sub-trial 3: Absorption Aim: To investigate whether a decreased absorption can be the cause of the low vitamin K status. Hypothesis: Absorption in the intestines is impaired. Method: A D-xylose test is performed. The participants are given a dose of 15g D-xylose dissolved in water and after one hour a sample of blood is collected to determine D-xylose in serum. Prior to this trial the patients need to be fasting.The patients are asked to fill out a FFQ concerning their intake of fat during the last month. Participants: 16

Sub-trial 4: Concentrations of dp-ucMGP is influenced by a low protein intake. Aim: To determine if a low protein intake influence the dp-ucMGP analysis method. Hypothesis: The analysis method (dephosphorylated-uncarboxylated MGP) is influenced by the patients' protein intake. Method: Patients are given a daily protein supplement for 14 days. Before and after the intervention a blood test is collected and the concentration of dp-ucMGP is determined and compared. Moreover, the patients are asked to fill out a FFQ concerning their intake of protein during the last month. Participants: 16

Sub-trial 5: Intervention with vitamin K Aim: To investigate whether a diet or supplement with tablets is best for improve vitamin K status. Hypothesis: If the intake of vitamin K is insufficient the diet rich in vitamin K should be sufficient. However, if absorption is compromised or vitamin K is influenced by dialysis a larger dose of vitamin K might be necessary. Method: This trial lasts for 15 weeks divided in two periods of six weeks and a three week wash out period in-between. One period focuses on a diet rich in vitamin K while dealing with the possible restrictions on phosphate, potassium and fluid for hemodialysis patients. The intervention in the other period consists of a supplement of 360μg Menakinon-7/day. Blood samples are collected at the beginning, middle and end of both periods. These blood samples are analyzed to determine dp-uc-MGP during the intervention period. Moreover, coagulations factor 2, 7, 10, vitamin A and D status and calcification propency score analysis will be done as well if the funds allow it. Patients are asked to fill out a questionnaire concerning physical and mental wellbeing and the presence of bruising at the beginning and end of both periods to determine whether vitamin K has an effect. Participants: 24