Circadian (2): The Sleep
Ever wondered what happens inside your body depending on the time of day? The difference is quite literally like night and day. Today, we’re going to look at some of those changes, starting with the body’s concept of midnight.
In a healthy, functioning body, midnight is registered between two middays. Remember, the body cannot see the clock on the wall, so you have to understand how the body "sees" time. Our biological midnight isn’t necessarily 12:00 AM; rather, it is the period of deep darkness that lies roughly halfway between two major periods of sunlight.
When we experience this midnight, we should be deep in slumber. The body produces the magic hormone melatonin, which helps guide our sleep stages. We can sleep for as long as we want, but if there isn’t enough melatonin, we won’t be able to cycle through the stages of sleep our biology requires. If you are a light sleeper, you may want to look into how your melatonin levels are affecting you. This hormone is responsible for pulling you into NREM Stage 2 sleep, which allows you to ignore those minor sudden bursts of noise that would otherwise wake you up. It also lowers our body temperature—a mandatory requirement for the brain to enter slow-wave sleep (NREM Stage 3).
From another perspective, the brain needs a "deep clean" after a long day. The cleaners of our brain are called glutathione. You might recognise the name if you’ve researched supplements for brain fog, but you’ll be pleased to know we already have plenty of it within us. We make this cleaning process possible via a mechanism called the Pentose Phosphate Pathway (PPP). Glutathione is ineffective if we can’t get the PPP going, as our raw supplies wouldn’t last a week. This is why we can’t survive without sleep for seven days. We store roughly 12–15 grams of glutathione at any given time and use up about 3 grams each night. The PPP ensures that used glutathione is recycled back into its active state so the supply remains virtually infinite. What turns the PPP on in a big way? Melatonin, of course.
This same hormone is known for anti-inflammatory properties that make your go-to tablets look like dwarfs in comparison. Unlike ibuprofen, melatonin is lipophilic, meaning it binds to fats easily—and there is fat everywhere in your body. Consequently, it reaches every cell to turn off the inflammatory signals that might otherwise cause "inflammatory storms." It does all of this without damaging your gastric lining, causing reflux, or upsetting your bowels.
While melatonin is a major player, it isn't the only hormone that distinguishes night from day. There are quite a few other changes that happen in our body during this time. We produce prolactin and parathyroid hormone at night, and we increase our immune function and modulation. Interestingly, we produce more occludin during this period, which keeps the space between our cells tight and the gut barrier secure while we rest.
We also make glucose in our liver as discussed in the ‘Insulin’ blogs. We convert a lot more T4, the thyroid hormone, into reverse T3 (‘Iodine’ blogs). Growth hormone is synthesised at NREM III to allow for physical repair and muscle growth - this sleep stage is commonly a focus among athletes today. We make lots of leptin to make us resistant to hunger, otherwise we would be raiding the fridge every hour of the night. You will thank your body after what I’m about to tell you next - we make antidiuretic hormone to stop us having to go for too many toilet visits when we should be sleeping. We (both men and women) make testosterone primarily at night, and rely for its supply to last us until the next night.
As we approach the end of the night, other hormones take the stage. The thyroid stimulating hormone (TSH) is produced to prepare for the coming day, and cortisol begins to rise until it peaks to wake us up. Alongside cortisol is DHEA, which limits cortisol’s impact on the rest of the body—you don’t want to wake up with heart palpitations from a stress hormone! As melatonin production subsides, noradrenaline and dopamine reclaim the brain to stimulate wakefulness. We become less sensitive to GABA, and our hypocretin neurons take the reins once again, leading us into another productive day.