Study design: A double-blind randomized placebo-controlled human intervention study in which 90 patients with clinically proven asthma will participate: 45 in the intervention group receiving plant stanol yoghurt and 45 in the control group receiving a control yoghurt without added plant stanols. At the end of the run-in period as well as at the end of the experimental period blood will be sampled to isolate PBMCs. These cells are used to evaluate effects on cytokine production, phagocytic capacity of neutrophils, and the activity of NK cells. In addition, the golden standard to show improvements in immune function is by showing an elevated Immunoglobulin response to a vaccine. Therefore, during the experimental period all subjects receive a vaccination against Hepatitis A Virus. After 1, 2, 3, and 4 weeks blood will be sampled to monitor specific immunoglobulin titers to HAV.