Monday, March 14, 2011

Sleep, Seasonal Hormonal Varation, Genetic Adaptation

During sleep, you make another hormone called prolactin, When the nights are long, as in winter, your prolactin has come down by the time you wake up. But in the summer, when the nights are short, prolactin spills over into the daytime. This is a key point when considering WHY we overeat (specifically carbohydrates).
When prolactin spills over into the daytime, it suppresses a hormone called leptin. Leptin is your body’s fat monitor. [T]o make it simple, leptin goes to the brain and pushes the OFF button on your Neuropeptide Y (NPY). When NPY is turned on, you crave carbohydrates. This is why your ancestors loaded up on fruit and carbs as much as they could during the spring and summer. They were driven to do it by NPY! Why? Because the short nights gave them “prolactin spillover”, thus suppressing leptin, and leaving carb-craving NPY cranked up.
Of course, all of this “carbing-up” made them insulin resistant, which was actually a good thing back then. [Seasonal] insulin resistance and the fat it stores isn’t really a problem when your life depends on it.
Let’s fast-forward to the early 20th century and the invention of the light bulb. Now, with the flip of a switch (or the clap of our hands) we can manipulate the seasons. Long days. Short nights. Year round.

If you read the rest of this post from Sean at UW, you could just about skip the very tough to read but fascinating "Lights Out".  The short version?  If you think agriculture changed things 10,000 years ago (imagine your hunger gatherer ancestors getting six inches shorter and losing their teeth whilst getting fat and sick), and if you think the advent of the industrialized food chain changed things (imagine mass produced vegetable based "franken oils" followed up by reutilization of soy waste as "soy products", and shudder), you should also be concerned with what the advent of Thomas Edison's revolutionizing invention did also.  Yes, completely changing the sleep cycles of entire populations in very short order probably has had an impact!

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