The mind influences the immune system directly via the nervous system. The placebo effect achieves measurable healing rates of up to 50% — not because of imagination, but because suggestion triggers real neuroimmunological changes. The nocebo effect shows the flip side: negative beliefs can seriously damage the body. "Laughter is the best medicine" — scientifically proven.

The nervous system translates mental states into physical responses — via neuropeptides, the cortisol axis and the autonomic nervous system. Chronic stress leads to dysregulation: elevated cortisol suppresses immune cells. Just 2 nights of sleep deprivation impair immune functions that do not fully normalise even after 3 nights of normal sleep.

A "strong" immune system doesn't mean maximally active — it means correctly regulated. NK cells rise after acute exercise. Oxytocin (triggered by social closeness & hugs) measurably improves immune function. Autoimmune diseases often arise from overactivity in the wrong area — not from too little activity.