Essentials: Using Science to Optimize Sleep, Learning & Metabolism

**Andrew Huberman** (0:00)
Welcome to Huberman Lab Essentials, where we revisit past episodes for the most potent and actionable science-based tools for mental health, physical health, and performance.
I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. Today is episode three of the podcast, and it is office hours. Office hours, as many of you know, is where students come to the office of the professor, sit down and ask questions, requesting clarification about things that were confusing, or to simply go down the route of exploring a topic with more depth and detail. Somebody asked, what is the role of moonlight and fire? I'm presuming they mean fireplace or candle or things of that sort. In setting circadian rhythms, is it okay to view moonlight at night, or will that wake me up? Will a fire in my fireplace or using candlelight be too much light? Great question. Turns out that moonlight, candlelight and even a fireplace, if you have one of these roaring fires going in the fireplace, do not reset your circadian clock at night and trick your brain into thinking that it's morning. Even though if you've ever sat close to a fireplace or even a candle, that light seems very bright. And there are two reasons for that that are very important. The first one is that these neurons in your eye that I discussed in the previous episode, these melanopsin ganglion cells, also called intrinsically photosensitive ganglion cells, those cells adjust their sensitivity across the day. And those cells respond best to the blue-yellow contrast present in the rising and setting sun, so-called low solar angle sun, also discussed in the previous episode. But those cells adjust their sensitivity such that they will not activate the triggers in the brain that convey daytime signals when they view moonlight, even a full moon, a really bright moon or fire. Because we talked about just how crucial it is to avoid bright lights between the hours of about 10 p.m. and 4 a.m., except when you need to view things for sake of safety or work and so forth. I also received a lot of questions about red light. In principle, red light will not stimulate the melanopsin retinal neurons that wake up the brain and circadian clock and signal daytime. However, most of the red lights, in particular, the red lights that come on these sheets of these products that people are supposed to view them in order to access a number of health effects, those are way too bright and would definitely wake up your body and brain. So if you're thinking about red light for sake of avoiding the negative effects of light later in the day and at night, then you want that red light to be very, very dim. Certainly much dimmer than is on most of those commercial products. Now, do you need red lights? No, although red lights are rather convenient because you can see pretty well with them on. But if they're dim, they won't wake up the circadian clock. They won't have this dopamine disrupting thing that we talked about in the previous podcast. Okay, a huge number of people asked me about light through windows. Setting your circadian clock with sunlight coming through a window is going to take 50 to 100 times longer. You can download the free app Light Meter. You can have a bright day outside or some sunlight. Hold up that app, take a picture. It'll tell you how many lux are in that environment. Now close the window. And if you want, close the screen or don't open the screen. You can do all sorts of experiments. You'll see that it will at least half the amount of lux. And it doesn't scale linearly, meaning let's say I get 10,000 lux outside, 5,000 looking out through an open window. And then I close the window and it's 2,500 lux. It does not mean that you just need to view that sunlight for twice as long if it's half as many lux, okay? It's not like 2,500 lux means you need to look for 10 minutes and 5,000 lux means you look for five minutes. It doesn't scale that way just because the biology doesn't work that way. Best thing to do is to get outside if you can. If you can't, next best thing to do is to keep that window open. It is perfectly fine to wear prescription lenses and contacts. Why is it okay to wear prescription lenses and contacts when those are glass also? But looking through a window diminishes the effect? Well, we should think about this. The lenses that you wear in front of your eyes by prescription or on your eyes are designed to focus the light onto your neural retina. So let's think about why I'm making some of these recommendations because I think it can really empower you with the ability to change your behavior in terms of light viewing and other things, depending on time of year, depending on other lifestyle factors. The important point to understand is that early in the day, your central circadian clocks and all these mechanisms are looking for a lot of light. Okay, I want to talk about seasonal changes in all these things as they relate to mood and metabolism. So as all of you know, the earth spins once every 24 hours on its axis. So part of that day, we're bathed in sunlight, depending on where we are. The other half of the day or part of the day, we're in darkness. The earth also travels around the sun 365 days is the time that it takes one year to travel around that sun. The earth is tilted. It's not perfectly upright. So the earth is tilted on its axis. So depending on where we are in that 365 day journey, and depending on where we are in terms of hemisphere, or northern hemisphere, or southern hemisphere, some days of the year are longer than others. Some are very short, some are very long. If you're at the equator, you experience less variation in day length and therefore night length. And if you're closer to the poles, you're going to experience some very long days, and you're also going to experience some very short days, depending on which pole you're at and what time of year it is. The simple way to put this is depending on time of year, the days are either getting shorter or getting longer. Now, every cell in your body adjusts its biology according to day length, except your brain, body and cells don't actually know anything about day length. It only knows night length. And here's how it works. Light inhibits melatonin powerfully.