Despite what your cat, your boss, your baby or your algorithm might say, 1am is not a good time to be awake.
People aren’t possums, and while sitting in a tree at midnight eating your neighbour’s tomatoes might be fun occasionally, it isn’t a sustainable life plan.
The fact is, humans have evolved be awake during the day and asleep at night, and if we try to mess around with this schedule it’ll catch up with us in the long run.
Circadian rhythm (and blues)
For millions of years our ancestors settled down at sunset and woke up with the dawn – and our body remembers that, even if we don’t.
The way this all works has to do with the big clock inside your brain and the little clocks inside your cells. Ideally, these all synchronise to set the daily schedule for your body – the circadian rhythm.
“Circadian rhythms are these 24 hour patterns of physiology and behaviour, like how our body temperature, our blood pressure, oscillates across the day” explains Professor Morag Young, a leading researcher in cardiovascular endocrinology at the Baker Heart and Diabetes Institute.
Every cell in your body contains a tiny mechanism that operates on a 24-hour cycle. This keeps the cell in a neat routine of consuming energy during the day and running repairs during the night.
But you also have a central clock – the suprachiasmatic nucleus (SCN) in your brain that is activated by light. This instructs the body to wind up or wind down depending on what it perceives as the time of day.
And like any house with three trillion clocks, it’s best if all they sync up with each other, and with reality, otherwise there are alarms going off at all random hours.
But staying up late, eating at weird hours, or beaming Youtube into your eyes at 3am can confuse this system and cause circadian misalignment – when your brain thinks it’s sunrise, your toes think it’s dinnertime, and your heart is awkwardly caught somewhere in the middle.
The hormones that put the tick in your ticker
Hormones are key to this process. They’re like the microscopic postmen of your body, carrying urgent chemical messages between organs. In the morning the SCN sends out “time to get up!” messages so your body knows to switch from night mode to day mode.
Cortisol, the stress hormone, is the most famous of these couriers. Just before you wake up the SCN sends a signal to increase cortisol levels, which then runs around like a mad thing getting the body all pepped up and ready for consciousness. Then, as the day goes on, cortisol levels decrease.
Cortisol isn’t the only clock-linked hormone. The SCN also prompts your body to produce melatonin across the day, slowly building up ‘sleep pressure’ until your brain starts begging for pyjamas.
“Our bodies need to produce melatonin across the day because partly the melatonin can control what’s happening with our clocks, but it also builds up the levels build up over the course of the day.” explains Professor Young. “That provides what’s called sleep pressure. So you go ‘yawn, 9 o’clock, really getting tired, should go to bed soon.’”
“That circadian pattern of cortisol release is really well known,” says Professor Young. “And we know from years and years of research that if that rhythm is dysfunctional, we can have metabolic disease, we can have poor healing – it really messes up a lot of our physiology.”
“But what our work has identified is that there’s a second receptor system that appears to be helping keep the clock ticking in time.”
Young’s research shows that there’s another type of hormone receptor that appears to be crucial to our internal timing. The mineralocorticoid receptor, long known for its role in regulating blood pressure and fluid balance, is now emerging as a crucial cog in the circadian clockwork.
Young’s team has shown that this receptor plays an essential role in keeping the clocks in our heart cells ticking along smoothly. When it’s disrupted, parts of the heart start showing signs of stress and dysfunction.
“If we disrupt those systems,” she explains, “they will have a negative impact on how we control blood vessel function, cardiac function, and renal function, and how we’re regulating our fluid balance.”
The sun and the restless
This has implications for anyone who regularly stays up late – but especially for night workers, shift workers and people who travel a lot. When your schedule is out of sync with your circadian rhythm, your body is sustaining damage.
The SCN is activated by short-wavelength light: blue light. This means that when we’re looking at our phones at night our brains are seeing a tiny rectangular sunrise.
“You’re giving yourself light information that’s the same sort of light that you should be getting in the morning. You should not be getting that at night when you’re in your rest phase.” advises Professor Young.
“Some phones have a setting where you can switch to yellow light. I don’t think it’s perfect, but it’s better than flashing blue light into your eyes. If you’re not doing that already, I strongly recommended it.”
Apart from all the other junk our phones tell us, they also tell our brain that it’s early in the morning when it’s only 10pm.
This delays the release of melatonin, which in turn delays everything else: digestion, blood pressure, immune response, tissue repair.
It’s not just that you’re staying up late like a cool rebel. It’s like you’ve surfed the internet and come back with jet-lag.
The revenge of the sandman
“It’s a form of stress, not getting enough rest!” says Young.
And it shows: “When we did our analyses, even when you account for all of those other risk factors, we could still see an independent impact of poor sleep.”
“When we looked at sleep length by itself, it really stood out as a significant regulator of blood pressure. Why is this so? We think it relates to increased cell injury and disrupted regulation of physiological processes.”
“Cell metabolism and energy production is meant to be separate from DNA repair and replication and cell clocks help to separate these processes in time. [By under sleeping or sleeping at the wrong time] we’re blurring the line between cell repair process processes and metabolism.”
“It’s really important that we separate those functions. if we’re not achieving that, we’re going to be setting ourselves up for tissue injury”
But the answer to the brain/body/one more episode conundrum isn’t just to sleep more. Oversleeping also has consequences, especially if it means you miss out on morning light.
“You would sort of think more is better – but it’s not,” says Young. “What’s important for setting our circadian rhythms and setting the timing in our system is exposure to short wavelength bright light, which is highest in the morning. We need that early morning bright light in our eyes to set our clocks.”
Getting the short end of the shift
Studies have found that even one night of poor sleep can trigger measurable metabolic dysfunction – but long-term shift workers who stay up every night are particularly at risk of high blood pressure and heart disease.
Even if you’re a natural night-owl, you can still get social jet-lag from switching up your routine on weekend or to keep up with daytime friends.
But obviously shift workers can’t just all quit their jobs tomorrow.
Doctors, nurses, firefighters, paramedics, pilots, truck drivers and cleaners all keep our world running while the rest of us snuggle up with our teddy bears.
Young’s research is part of a growing effort to find ways to protect these important workers from the impact on their health their jobs might cause.
But at a personal level, the advice is fairly simple: make sure you get around 7-8 hours of sleep, get those screens yellow, and stumble outside in the morning to catch some rays before breakfast.
You may think you feel like death warmed up after a bad night’s sleep – but actually you feel like an increased risk of cardiovascular disease.
It’s not just you; your heart needs to rest too.
