What's better at boosting your body's defenses: a daily walk or a dose of Airborne, an immensely popular "immune support supplement"? Hint: It's not the one that Americans spend more than $100 million on each year. So why do we keep buying Airborne and similar products? Blame a psychological phenomenon called the illusory correlation: a strong belief in a connection between two things, even when there is none. Here's the way it works: We start to sniffle and drop some vitamin C, or echinacea. Then a few days later, when we start to feel better, we give all the credit to the supplement – even though it was really our immune system taking its natural course and knocking out the invaders.
Our beliefs are reinforced by outrageous, yet mostly unchallenged ads. In fact, a review of more than 30 studies suggests that vitamin C does not prevent colds, and the evidence for echinacea is iffy at best. And not one study shows that Airborne boosts anything more than its manufacturer's profits. In 2006, the Center for Science in the Public Interest got so angry about the company's "false advertising" that it joined a class-action suit that forced Airborne to pay out $23.3 million to consumers.