24 patients will be included in a double blind placebo controlled cross-over 8 week study comparing placebo to Niaspan (a long release formulation of niacin). In order to prevent any drop out linked to the flushing side effect of niacin, patient will take aspirin (300mg) prior to treatment throughout the study duration. The study will include at start and end of each arm, a full lipoproteins quantification as well as a measure of enzymes involved in lipid metabolism. On day 42 and 56 of each period, after an administration of either placebo or 500mg of immediate release niacin respectively, changes in plasma free fatty acid levels will be measured for 8hours in order to assess potential loss of activity of niacin over time upon chronic treatment with niaspan. Half of the patient will have an exploration of their glucose metabolism using hyperinsulinic clamp technique, whereas in the other half a metabolic turnover study using stable isotopes will focus on their lipoproteins, triglycerides and cholesterol handling. These explorations will be done at the end of each treatment period.