A couple of weeks ago, I started to feel run down. Immediately, I started thinking: do I need to change something in my diet? Do I need to exercise more or less?
Then, I thought about something simpler: sleep. It occurred to me that I had gradually started staying up later over the last couple months. It wasn't intentional, it sort of creeped up on me.
So then I started going to bed earlier. By the next day, my energy was back. Problem solved!
It's amazing how people (myself included) can overanalyze things. In my case, looking back it should have been obvious: if I was tired, then I needed to go to bed! It's not that complicated (Robb Wolf would be proud).
Another thing I noticed is that it's not just the sleep but the darkness that seems important. Even if I turn out the lights early but don't fall asleep right away, I still seem to get the benefits. So the break from light seems as important as the actual sleep.
I think a lot of people get away with less sleep because of their diet. They use coffee, sugar, and junk carbs as stimulants, and therefore it may appear that they do fine with less sleep. I think such a strategy will catch up with a person in the long run.
Maybe a Paleo diet reveals a person's true need for sleep? Without the stimulants, people may find they need more hours of sleep per night.