In addition, hardly any flu-like symptoms were observed. On average, Hof's immune response was decreased by 50 percent compared to other healthy volunteers. In accordance, the levels of inflammatory mediators in Hof's blood were much lower. We know that this hormone is released in response to increased autonomic nervous system activity and that it suppresses the immune response. Pickkers said: "After endotoxin administration, the increase of the stress hormone cortisol in Hof was much more pronounced compared to other healthy volunteers. During this experiment, various measurements were performed, including brain activity, autonomic nervous system activity and inflammatory mediators in the blood.
To investigate this, Hof was administered endotoxin while practising his concentration and meditation technique. Hof claims that he can influence his autonomic nervous system and thereby suppress his immune response through concentration and meditation. Wim Hof is well known for his remarkable activities in extremely low temperatures. These experiments are completely safe and have been performed on more than 240 subjects in our centre." The immune system reacts as if real live bacteria have entered the body and mounts an immune response characterized by the production of inflammatory mediators and flu-like symptoms like fever, chills and headache. Pickkers said: "We administer endotoxin, a dead cell-wall component of bacteria, to healthy volunteers. Professor Peter Pickkers and PhD candidate Matthijs Kox investigate the effects of the autonomic nervous system on the immune response. The immune system is, in part, controlled by the autonomic nervous system, a system which cannot be deliberately influenced. However, excessive activation of the immune system can cause tissue and organ damage. A well-functioning immune system protects us against viruses and bacteria.