“Positive feelings are signs of health; they do not cause good health,” says Howard S. Friedman, PhD, coauthor of The Longevity Project: Surprising Discoveries for Health and Long Life from the Landmark Eight-Decade Study (2011). “Thinking positive thoughts will not cause your cancer cells to decide to self-destruct, but it might help you get up and out of bed, eat your spinach, complete your chemotherapy, improve your digestion and get a good night’s sleep.”
It’s possible that optimism strengthens the immune system. But for cancer in particular, the evidence is “quite limited and unconvincing,” wrote researchers James C. Coyne, PhD, and Howard Tannin, PhD, in their skeptics’ argument for the Annals debate.
Plus, then you have to prove that it matters. “In some instances, tumors may even enlist the immune system to accelerate development,” they wrote. So strengthening it may not always be a benefit.