At baseline and after six months, also serum chromium will be measured. Extra citrate and serum collection tubes will be frozen for additional measurements, when needed. Also 24-h urine will be collected at baseline and after 6 months and volume, creatinine, protein and albumin will be measured. Three tubes containing both 2 cc of urine will be frozen for additional measurements. These (extra) analyses will only be made after given information and approval of the patient, and after approval of the medical ethical committee.