⚖️ Adenosine and it’s worst enemy

Your 24-ish-hour circadian rhythm isn’t the only thing that times your sleep and wake. The other is “sleep pressure” - an increasing desire to sleep. At this very moment, a chemical called adenosine is building up in your brain. High levels of adenosine quieten down brain-regions related to wakefulness while also promoting sleep-inducing processes. Adenosine increases with every minute that passes; the longer you are awake, the more adenosine will accumulate - with levels usually peaking after 12-16 hours of being awake and being cleared out after a night of sleep.

But there is one way to mute the sleep signal of adenosine and feel more alert and awake…. Caffeine: it has been called the most widely used (and abused) psychoactive stimulant in the world. Alongside oil, it is one of the most traded commodities on the planet.

Caffeine has a similar (but not identical) molecular structure to adenosine. As a result, it binds to adenosine receptors - often easier than adenosine itself! This means caffeine molecules end up stealing access to most of the receptors, leaving adenosine molecules with very few places to bind.

But unlike adenosine (which makes you sleepy), caffeine doesn’t do anything once it binds to a receptor. It simply just sits there - hijacking effectively inactivating the receptors. The result? Your body can no longer receive the sleepiness signal normally produced by adenosine. It can no longer gauge how tired you actually are, or whether you need rest. Instead of feeling sleepy at the right times, you are tricked into feeling alert and awake (regardless of how much adenosine could be circulating in your body)!

🥼 The caffeine files: forgotten NASA experiment might surprise you

In a long-forgotten 1995 experiment, NASA scientists exposed spiders to different drugs and then observed the webs that they constructed. Those drugs included LSD, speed (amphetamine), marijuana, and caffeine. The researchers noted how strikingly incapable the spiders were at constructing anything resembling a normal web when given caffeine, even relative to the other drugs tested.

📊 Want both coffee AND sound sleep? Here’s your cutoff for the day

As a summer intern in the City of London, I would get through several coffees a day (abusing both the free coffee machines on my floor). Despite my early bedtimes I would often wake up groggy and tired in the mornings - what I didn’t realise was how long a shot of caffeine can hang around in the body. Like many of us, I failed to make the link between a bad night of sleep I woke up from in the morning and the cup of coffee that was consumed the evening before.

Levels of caffeine circulating in your body peak about thirty minutes after ingesting a coffee. 99% is absorbed within 45 minutes. But caffeine has an average half-life of five to seven hours. In regular speak, this means that if you drink a cup of coffee around 6pm, by 12am that night, 50 percent of that caffeine will still be active and circulating throughout your brain tissue. In other words, at midnight you’re body is only halfway through recovering from the caffeine you drank after dinner.

Here’s what your caffeine levels would look like over the course of a day if you drank 3 cups of coffee, one cup at each of 8am, 10am and 4pm.

In this scenario, it’s 5am before caffeine levels fall below the 50mg threshold (which, according to the FDA, is the maximum amount of caffeine in your body where you can sleep restfully).

Caffeine is going nowhere; according to one population-based study (of Italians, no less) nearly seventy percent of people consume caffeine in the evening. Yet the evidence suggests that consuming 200mg of caffeine (approximately 2 small cups of coffee) as much as 6 hours prior to sleep can result in a loss of up to one hour of sleep. Caffeine negatively affects sleep stages 3 and 4 (deep sleep) through adenosine blocking, but it also increases sleep latency (the time it takes you to fall asleep). It seems to have milder, but still negative effects on REM sleep.

So what is the exact cut-off time you should be aiming for?

For example, this study shows that middle-aged adults experience increased disturbances in sleep, as measured by electroencephalogram (EEG) analysis, compared to young adults. Another study suggests that as little as two cups of coffee in the morning may have negative ramifications on your sleep that night, leading to a significant reduction in sleep efficiency and total sleep time.

🔍️ Actionable insight: Try it for yourself: caffeine levels simulator!

As a summer intern in the City of London, I would get through several mochas a day (I told myself they didn’t count as real coffee). Little did I know I was racking up a considerable amount of caffeine in my system. Here’s what a day of coffee-drinking would look like for my caffeine levels:

🛠️ My current Sleepstack:

• Screen filter software: Tools like f.lux (desktop), Twilight (Android) and Night Shift (iOS) change the colour of your display to based on the time of day to reduce overstimulating wavelengths.

• Sleep mask: I use this one at the moment. Light affects melatonin secretion even when your eyes are shut. A sleep mask is also a great alternative to investing in a set of blackout curtains; I never sleep without one now.