Journal Club with Dr. Peter Attia | Effects of Light & Dark on Mental Health & Treatments for Cancer

If you're out in the sun with no cloud cover or minimal cloud cover in the middle of the day at noon, chances are it's over 100,00 lux ... Most indoor environments, even though they might seem very bright, I like to think of kind of like a department store with a bright light, believe it or not, that's probably only closer to 6,000 lux maximum...

If you do see afternoon and evening sunlight... that can partially offset the negative effects of artificial light exposure at night. I think of this as your Netflix inoculation. The amount of melatonin suppression from nighttime light exposure is halved by viewing setting sun.

That's three things that we should all strive to do: View low-solar angle sunlight early in the day, view low-solar angle sunlight later in the day, and get as much bright light in our eyes as we safely can—ideally from sunlight throughout out the day.

Your retina is very insensitive to light early in the day. You need a lot of photons to trigger this mechanism early in the day. As the day goes on, retinol sensitivity increases, and it takes very little light to shift your circadian clock late in the day.

Turns out that dark exposure at night, independent of light exposure during the day, is important for mental health outcomes ... People who make it a point to get dark exposure at night, AKA the absence of light at night, actually benefit, even if they're not getting enough sunlight during the day, and this is especially true for people with certain mental health issues.

People are spending approximately 90% of their time indoors nowadays... And those indoor environments are simply not bright enough ... Some people are putting blue blockers on in the middle of the day, which is the worst thing you could possibly do.

There's a correlation between day length and mood and mental health such that, for many people... when days are longer in the spring and summer, they feel better; they report fewer depressive symptoms. And conversely, when days are shorter, significantly more people report feeling lower mood and affect.

In general, unless the light is coming directly through the window, most of the relevant wavelengths are filtered out ... However, if you have windows on your roof, which some people do, skylights, that makes the situation much, much better. In fact, the neurons that, in the eye, signal to the circadian clock and these mood centers in the brain reside mainly in the bottom two-thirds of the neural retina and are responsible for looking up. Basically, they're gathering light from above.

That's what happens when you look at morning sunlight—you're advancing your circadian clock. Translated to English or non-nerd speak, you're making it such that you will want to go to bed a little bit earlier and wake up a little bit earlier the next day.

On a cloudy day, when you're outside, it can be as bright as or an average of 100,000 lux—but it won't seem that bright because you don't 'see the sun.'

Better to get the morning light ... If you miss a day, no big deal. It's a slow integrative mechanism averaging across the previous two or three days. But if you miss a day, you want to get twice as much light in your eyes that next morning.

Some people like myself wake up before the sun comes up ... I think the best thing to do is simply to turn on as many bright lights as you can indoors to trigger that melanopsin mechanism... and then get outside once the sun is starting to come out.