NPR’s Morning Edition ran a story on finding the perfect balance of caffeine. Apparently as little as 100mg—typical for a 6-ounce cup of coffee—is enough to give most people a lift. Depending on tolerance, anxiety and jitters start showing up as early as 200mg.
And yes, a cup of plain coffee has more caffeine than a shot of espresso.
The story was followed by one looking at why children have so much more energy than their elders. One of the biologists they interviewed was Michael Rose, an evolutionary biologist at UCI. I actually took a class from him once, on an evolutionary approach to explain the aging process. His take on it is that youthful energy is all about exploring the world and filling up your brain. Once you’re an adult, you don’t need to explore as much. It also means you take fewer risks, increasing your odds of survival.