Not much. Here's how manufacturers can use the claim to sell us supplements we don't need. “Clinically proven,” says the ad for Longevity by Nature’s Telos95 Telomere Health Support. Take the supplement (made of grapevine and olive leaf extracts) to “reverse cellular aging” by lengthening telomeres​—the caps on our chromosomes—“by an astounding 80 percent.” Here are some of the tricks that the company used to “prove” that Telos95 works.