Have any well designed human studies shown a particular intervention is associated with a significant increase in lifespan? Call me skeptical, but we can't eve

Have any well designed human studies shown a particular intervention is associated with a significant increase in lifespan? Call me skeptical, but we can't even treat Alzheimer's and Parkinson's, and the leading cause of death in the US is still cardiovascular disease after decades of drug development Plus, unless these drugs enable immortality I'd imagine they would just enable more people to live to older age, and then more people would get high cost illnesses