I wish I knew the reason. It might be worth a book and some money if I could find out why and publish a study on it. I hope it is genetic - it would be a great trait to inherit! Of what do I speak? My dad is insanely healthy! He amazes his friends and his doctors. Dad is 90. He takes one prescription medicine a day, and we're not convinced he really needs it. He takes Galantamine., which is used to treat symptoms of Alzheimer's. Dad has been on the drug since his diagnosis. The disease hasn't progressed too terribly quickly and Dad seems to be holding steady with his memory issues. So, either the drug is working quite effectively or he doesn't have Alzheimer's. Other than that, Dad tries to remember to take an 81mg aspirin, Vitamin E and calcium daily. I put the OTC pills in a monthly dispenser box and Dad keeps the Galantamine on the dining table with a small calendar. Each day when he takes it he crosses off the day. He's usually very good at remembering to do this.... but he does forget the vitamins now and then. I'm not particularly worried!
So, if I ever discover the secret... I'll let you in on it!