NAM, well known as a dietary supplement, has also been extensively studied in humans in a variety of diseases in both children and adults. However, the bioavailability of NAM in patients with JIA at the side of inflammation, and therefore it’s potential as a therapeutic agent, is yet unknown. The primary objective of this study is therefore to assess the penetration of orally ingested NAM in the synovial fluid. In this phase II trial essential preliminary information will be gained on the peak NAM levels in the synovial fluid.