Lights Out: Sleep, Sugar, and Survival
The cover of the book pretty much says it all. The author makes the case that the single most important thing you can do to improve your health is simply to get enough sleep.
The basic reasoning is this: for most of our existence, man experienced long days in the summer and short days in the winter. Yes, we've had fire for thousands of years, but gathering flammable stuff to burn takes energy, and firelight isn't really all that great to work by, so we still mostly went to bed when it got dark until we invented electric lighting about 100 years ago.
Our ancestors survived to pass their genes down to us because they learned to get fat (and, in the case of women, pregnant) by August so that fat pad would sustain them all winter (and babies would be born just in time for the summer of plenty). The genes we got from them still carry the instincts to do exactly that.
How does it all work? While the book is an easy read for someone without a science degree, it really gets down into the nitty-gritty of how your body works. I'll try to distill the big points:
1. Your brain makes melatonin when it gets dark out. It stops making melatonin when it detects light--even if your eyes are closed. It makes prolactin shortly after it detects melatonin, which then circulates around your system for several hours. Melatonin is not just something that makes you sleepy, and prolactin isn't just for lactating. They're your immune system's fuel: they makes white cells, T cells, and NK cells. They're the reason sleep helps you get over illness.
2. Prolactin also makes you crave carbohydrates (because it suppresses leptin, the hormone that tells your brain you're full). Long nights mean prolactin is low when you wake up. Short nights mean prolactin is high when you wake up, your sugar craving is turned on all day. Plus, you're autoimmune (asthma or allergies much?) from all those prolactin-fueled T and NK cells running around attacking everything inside you.
3. Cortisol is the hormone that helps you deal with stress. It's produced when you're running around, jumping, climbing, worrying, frustrated, and--you guessed it--bathed in the light of long days, which long ago signaled mating season--stressful for the men competing over the women, and stressful for the women being pursued by horny men.
4. Your body makes insulin when blood sugar goes up. Blood sugar goes up when you eat carbohydrates, and when your cortisol levels are high. Insulin is the storage hormone. It lets your body convert carbohydrates into stored body fat and cholesterol.
Here's the crux of the matter: staying up all night means you spend your days pumped full of prolactin that makes you crave carbohydrates and the insulin to help you store them as fat. Try to exercise those carbs off? You'll just produce even more cortisol, and even more insulin as a result. This would be fine for 3-4 months a year, as was the case for thousands of years. Doing this 12 months a year is a recipe for diabetes, heart disease, obesity, depression, and a whole litany of other modern ills that have surged in the last 100 years.
There are whole chapters devoted to other biological processes, like the relationship between melatonin/insulin and dopamine/serotonin, or how your body digests and makes use of all the different types of food you eat, or the fact that numerous scientific studies point to high levels of melatonin as protective against cancer and low levels of melatonin as cancer-causing.
I really enjoyed this book and can't summarize here all the details or even all the highlights, but I love that I now understand the way my body works. When I talk to doctors at work now, I speak their language because I understand the complex relationships between environmental cues, diet, and all the various endogenous hormones and symbiotic bacteria swimming around inside me.
As for the way the book has impacted my life aside from increasing my knowledge base, I've begun turning off the lights and going to bed earlier. And without even trying that's led to the following outcomes:
I wake up without an alarm clock.
I don't crave carbohydrates, and have all but eliminated bread and pasta from my diet with very little effort.
My mood is stable throughout the day and throughout the week.
I have stable, non-jittery energy all day long, without needing a nap around 4pm.
I have mental clarity and focus all day.
All in all, some pretty awesome dividends from reading this book. It was a pleasurable read, sprinkled with research, metaphor, and even a couple jokes here and there.
"Won't going to bed at 9pm affect your social life? Sure, but so will diabetes and cancer."
