So all these clocks work together to give us daily rhythms in sleep, metabolism, mood and even gut microbiome. But how are these clocks connected to the outside world? In fact, every morning as we wake up and open our eyes, bright light goes through our eyes and resets or synchronizes this clock, so that when daylight savings time changes, or when we move from one time zone to another time zone, light synchronizes all of our clocks to the new season or the new time zone. But the property of light that resets our clock is very different.
Almost 15 years ago, we discovered a new blue-light-sensing protein called melanopsin. It’s present only in 5,000 squiggly neurons in our eye. And these light-sensing neurons are literally hard wired to our brain clock, to the master circadian clock. But they have a very interesting property. They’re less sensitive to light, and especially to orange colored light. So that means, in the evening, as we move around and find our way under candle light or dim orange light, the melanopsin is not activated. It sends a signal to the brain as if it’s dark outside so that the brain clock makes a lot of melatonin and we get a good night’s sleep.
And in the daytime as we wake up, go outside for at least an hour or so. The daylight is very rich in blue light. It fully activates melanopsin. That synchronizes the brain clock nicely with the day. It reduces sleepiness and depression, and increases alertness.
But the problem is, we spend more than 90 percent of our time indoors. And at nighttime, bright screens and bright light activates melanopsin; it sends a confusing signal to the brain, and the brain thinks it’s not night yet, so it produces less melatonin, and we sleep poorly.
The next day when we wake up, as we spend most of our time indoors, this indoor light is not rich in blue light, so it again sends another confusing signal to the brain, and the brain thinks it’s not day yet. So all the chemicals that should boost our mood are actually not produced enough. So we kind of go back and forth between insomnia and fogginess, and if it continues for weeks or months, then a lot of diseases can happen.
And what is interesting is, this is particularly important for children because their brain is still developing. And when children go through early childhood circadian disruption, they are more prone to diseases like ADHD and autism. So this new simple idea, that we need more bright blue light during the daytime and less light, or darkness, at nighttime, is starting a new lighting revolution. And you are just getting a glimpse of this new light revolution when your smart screen and computer screen dim down and turn orange at nighttime. But there is more to it.
Just think about it: Circadian lighting at daycare and schools will promote healthy brain development and promote learning. Circadian lighting at home, factories, offices, will promote alertness and improve productivity. Circadian lighting at hospitals or retirement homes will promote health and accelerate healing. And in fact, right now, there is new circadian lighting in our International Space Station to promote productivity of our astronauts and make them have better nights’ sleep. So light is not the only factor that affects our clock.
In fact, just like light in the middle of the night disturbs the brain clock and breaks the chemical balance in our brain, food at the wrong time can disturb the peripheral clock and break the metabolic balance in our body, and that will push us towards disease.
Now, let’s figure out how. So in the morning, our stomach is actually ready with the right amount of hormones and digestive enzymes, and even good gut microbiome to digest food. So after we eat our first breakfast, a body absorbs enough carbohydrates and uses it to fuel our body. At the same time, it saves a little bit of nutrient as fat.
As we continue at lunch and dinner, the same process continues. And after the last dinner, last bite, a body slowly goes low on carb. At the same time, the circadian clock cranks up morning fat. And after a few hours, the clock turns into a reset and repair rejuvenation mode. That means that it turns on enzymes that will break down cholesterol and toxins.
It also turns on mechanisms to repair the DNA that we have damaged during the daytime. And a lot of cells that are damaged on our stomach lining or our skin lining are also replaced with healthy new cells so that allergy-causing chemicals or bacteria cannot get into our body. So after 12 to 16 hours of fasting, when we eat our next breakfast, the cycle of nurture, rejuvenation continues. But imagine if we delay that last bite late into the night. So in this case, this daily rhythm in metabolism becomes shallow.
There is not enough time to burn fat, and there is not enough time to break down the toxins, cholesterol, etc. So, you can imagine that somebody who eats within ten hours might have a much better circadian rhythm, whereas somebody who eats within 15 hours may not. To test this idea, we went back to the old lab and brought two identical groups of mice born to the same parents, raised in the same room, same age. And one group of mice got the standard Western diet to eat whenever they wanted. And then the second group was trained to eat the same number of calories from the same food, but they had to eat everything within eight to 12 hours at nighttime when they’re supposed to eat.