The way doctors treat illness today "is simple," wrote S. Jay Olshansky, a demographer at the University of Illinois. "As soon as a disease appears, … - David A. Sinclair

After a few billion years of advancement since the days of yeast, they have evolved to control our health, our fitness, and our very survival. They have also evolved to require a molecule called nicotinamide adenine dinucleotide, or NAD. As we will see later, the loss of NAD as we age, and the resulting decline in sirtuin activity, is thought to be a primary reason our bodies develop diseases when we are old but not when we are young.

On average, Americans consume more than three times the amount of food they need to survive and about 250 times as much water.14 In return, they produce 4.4 pounds of trash each day, recycling or composting only about of a third of it.15 Thanks to things such as cars, planes, big homes, and power-hungry clothes dryers,16 the annual carbon dioxide emissions of an average American are five times as high as the global average. Even the “floor” — below which even monks living in American monasteries typically do not go — is twice the global average.17 It

I take 1 gram (1,000 mg) of NMN every morning, along with 1 gram of resveratrol (shaken into my homemade yogurt) and 1 gram of metformin.7 • I take a daily dose of vitamin D, vitamin K2, and 83 mg of aspirin.