In December of 2005, a team of Australian researchers scientifically confirmed a long-suspected link between emotional stress and illness. The group from Sydney's Garvan Institute discovered that a hormone called neuropeptide Y (NPY) is released into the body during times of emotional stress. This hormone undermines the body's immune system and literally makes you sick.

According to the Institute's Fabienne Mackay: "During periods of stress, nerves release a lot of NPY, and it gets into the bloodstream where it inhibits the cells in the immune system that look out for and destroy pathogens in the body." She added, "That stress makes you sick is no longer a myth; it is a reality and we need to take it seriously."