This story was first published July 16, 2022 and resurfaced as the Listener brings back its best health content.
Research into circadian rhythms reveals the vital importance of our body clocks to our health and wellbeing. By Ruth Nichol
If you want to sleep well, get a dog. Those early-morning walks provide regular exercise, which we know is good for sleep. But as Russell Foster, a British neuroscientist who specialises in the study of circadian rhythms, points out, they also expose you to the early-morning light we all need to keep our internal body clocks – most of which run at about 24 hours and 10 minutes – aligned or “entrained” with the 24-hour day.
The result: better, more regular sleep. "People who own a dog have been shown to have better sleep, and you might think, 'What's that all about?' Of course, it's because they have to take their dog out in the morning and that's where they get their photon shower – their entraining light," says Foster, author of Life Time, which looks at how our bodies are governed by a 24-hour circadian clock.
Without that early-morning exposure to light – preferably at least 30 minutes outside where light is much brighter, although sitting inside by a window is acceptable if it’s raining – our internal clocks would eventually become misaligned with the external clock. We would start to go to bed about 10 minutes later every night and eventually our sleep-wake pattern would be totally out of sync with the 24-hour day.
That is what happens to people whose eyes are destroyed because of an accident of some kind. As a result, they lose the specialised cells in the retina called photosensitive retinal ganglion cells (pRGCs). These cells provide vital information about the overall amount of light around at dawn and dusk to a part of the brain called the suprachiasmatic nucleus (SCN). Without pRGCs, our bodies have no way of knowing where we are in the light-dark cycle and the result is a complete loss of any kind of 24-hour rhythm.
A former soldier whose eyes were destroyed in combat told Foster, “I am at my wits’ end, suffering from variable bedtimes and wake times, and I am very often sleepy during the day and awake all night. I’m slowly becoming isolated from my family and friends.”
Interestingly, people who go blind but whose eyes are still intact don't experience this disruption. They may not be able to see light, but their eyes can still detect it and send the appropriate information to the SCN.
Foster, who is professor of circadian neuroscience at the University of Oxford, describes the SCN as the body’s master clock. It helps to keep all the other biological processes that take place inside our bodies on track. This includes what happens in the liver, the muscles and the pancreas – in fact, probably every cell in our body. They all have their own 24-hour cycle, which keeps time with the master clock. However, once we start doing things at times our bodies don’t expect us to – such as eating or being awake – the clocks no longer work together and the results can be serious: heart disease, type 2 diabetes, obesity, as well as poor cognition and irritability.
"The SCN is rather like the conductor of an orchestra; it provides a time signal that co-ordinates the rest of the body," says Foster. "Without the SCN, everything drifts apart. So, instead of a symphony, you have a biological cacophony and a failure to do the right thing at the right time."
Even seemingly innocuous changes can have unexpected consequences, such as moving our main meal from the middle of the day, as was the case in the past, to the evening, as is the case now. Our bodies are designed to metabolise food better earlier in the day. Eating later appears to be a contributing factor in metabolic problems such as obesity and type 2 diabetes.
"In the course of three or four generations, we've moved our eating habits, and they're now misaligned with when our biology is regulating our metabolism," says Foster. "That's the worst possible scenario that anybody could have for type 2 diabetes, obesity and all the rest of it, because we're eating when our biology is not ready for it."
But what is really driving many of our current health problems is what he calls the "invasion of the night with light". Although for millennia we had no choice about when we got up or went to sleep, artificial light means we can now stay up much later – or even all night if we want to. It has also made it possible for us to create a society that is dependent on having people working at night, from healthcare workers to truck drivers and supermarket shelf packers.
For millions of us, this has resulted in what Foster calls sleep and circadian rhythm disruption. It can be caused by insomnia, jet lag, getting too little sleep, sleeping at the wrong time, or simply staying up too late on a regular basis.
At the heart of it, Foster believes, is a failure to appreciate the vital role that sleep plays in keeping us healthy. He says getting about 7.5 to 8 hours of sleep a night (it can be more or less depending on the individual) isn't an optional extra: we need it so our bodies can undertake the essential biological activities that allow us to function during the day. Sleep is a time to consolidate our memories, clear toxins and rebuild metabolic pathways – all of which are essential to maintaining, physical, cognitive and emotional health.
"In short, during sleep, the body performs a broad range of essential functions without which performance and health would fall apart rapidly."
The way things fall apart once those functions no longer take place are much more wide-ranging than you may imagine. Women who work night shifts or experience frequent jet lag, for example, are more likely to have disrupted menstrual cycles and abnormal levels of reproductive hormones. This makes it harder for them to get pregnant.
Those affected by disrupted sleep also pay a price in their personal lives. People who work night shifts are up to six times more likely to get divorced than those who work during the day.
"In addition to all the physical health problems associated with chronic tiredness among night-shift workers, you've got lack of empathy, you've got impulsivity, you've got failure to consolidate memory and you've got irritability. So, it's as if the person you married and decided to share your life with has turned into a monster."
The lack of sleep experienced by night-shift workers also puts them at greater risk of having a car accident on the way home from work. Foster says one study, published in the medical journal Anaesthesia, showed 57 per cent of junior doctors in the UK had either had a crash or a near-miss on the journey home after a night shift.
Lack of sleep has also been associated with a number of notable industrial accidents: it's no coincidence the Chernobyl explosion happened at 1.23am. Worryingly, now that many of us are about to resume international air travel, the cognitive problems found in night-shift workers have also been found in long-haul airline pilots and aircrew.
There's also growing evidence that shortened and disrupted sleep during the middle years increases your chance of developing Alzheimer's when you are older. The reason may be that, according to recent research, sleep helps to clear the brain of a protein associated with Alzheimer's called beta-amyloid.
"Even one night of no sleep has been shown to increase levels of beta-amyloid within the cerebral spinal fluid and deep within the brain," says Foster.
The lesson from that finding, he says, is that it's important to protect sleep in the middle years. "I wouldn't say poor sleep causes dementia, but I think in those vulnerable individuals it might be a contributing factor."
As for celebrating the hard-driven business people who apparently survive on just a few hours' sleep a night, Foster says that is complete folly. They may seem to be coping but it's almost certain that their rigorous, sleep-deprived schedules will take their toll eventually.
"The analogy I use is that it's a bit like driving a car. You go into first gear and you've got that wonderful acceleration. You go, 'Wow, this is amazing.' But then if you keep the engine in first gear you're going to destroy the engine. It's fine short-term, but if you carry on and on and distort biology outside the norm, if you override it constantly, then you're heading for problems."
Foster accepts that when it comes to our 24/7 society, we can't put the genie back in the bottle. But we can find ways of mitigating its more serious consequences, by, for example, providing junior doctors with a simple vigilance app that goes on the dashboard to measure eye-roll or head-nod and alert somebody that they're falling asleep.
Similarly, employers could provide protein-rich, easy-to-digest small meals to their night-shift workers, rather than high-fat, high-sugar foods that are even more likely to make them gain weight if they eat them during the night.
For older people living in rest homes, simply exposing them to higher levels of artificial light during the day could help improve their cognition. One American study found that older people in this environment were exposed to only 10 minutes of 2000 lux of light a day (2000 lux is equivalent to the light you would get outside at midday on an overcast day).
"Part of the mental decline in the nursing-home environment may be the result of a weak light-dark cycle, which leads to a slide into poor memory, poor sleep and, therefore, reduced cognition."
One of Foster’s slightly more contentious views is the impact of the blue light that comes from devices such as smartphones, laptops and e-books on our sleep. The conventional view is that this light affects our circadian rhythm, which then affects our sleep, so these devices should be avoided before bed. Foster agrees that they should be avoided before bed, but not because of the effect of the blue light they emit, which, he says, is too low to affect our body clocks, but because they put us into a state of alertness.
"The key thing is that it's not the light from these devices, it's the alerting effect your smartphone has, where you're switching between emails and social media and the news and maybe even a YouTube video. We do know for sure that these devices have an alerting effect on the brain and that will, indeed, delay sleep onset."
Our growing understanding of how circadian rhythms work isn’t just focused on what we’re doing wrong. It’s becoming clear that we can use that understanding as a force for good.
We now know, for example, that we have a better immune response during the day, as that's when we are out and about and more likely to encounter pathogens such as bacteria and viruses. The immune response starts to wane as the day progresses, which has implications for the timing of vaccines.
A 2016 study published in the journal Vaccine found that elderly people who were vaccinated against the N1H1 flu virus in the morning had an antibody response three times higher than those who were vaccinated in the afternoon. Similar research is now being carried out on the timing of Covid-19 vaccinations, to see if administering them in the morning provides greater protection.
The timing of when we take certain medications can also make a difference in how effective they are, and Foster says that harnessing the power of the body clock may also result in new treatments for cancer.
"It seems that the circadian clocks in cancer cells are turned off because the clock acts as a break on cell division. If you turn the clock back on in a cancer cell, you can hugely reduce tumour progression, which is a potential treatment for cancer."
Other possibilities include developing new drugs that will correct circadian rhythm disruption in the profoundly blind, or in those who have genetic or developmental disorders that affect their circadian rhythm.
"I can see this whole new area opening up," says Foster. "It's such a privilege to work with my younger colleagues who will carry the torch forward and transform medicine.
“I genuinely believe that, in the next 10 to 20 years, we will have brand-new therapies and brand-new interventions to attack some of our most ferocious diseases.”
Timing is everything
Drugs to treat conditions such as high blood pressure and heart disease are prescribed to hundreds of thousands of New Zealanders every year. But could the time people take them affect how effective they are?
British neuroscientist Russell Foster says because everything in our body is tied to the finely balanced rhythms of our body clock, there’s an ideal time to take many drugs to make them more effective. This includes blood-pressure medication, anti-clotting drugs such as aspirin and some statins, which slow down the production of “bad” cholesterol that can contribute to heart attacks and strokes.
The chances are that right now you’re not taking these drugs at the optimal time.
Many doctors suggest taking antihypertensives and aspirin first thing in the morning, and from a practical point of view, that makes sense: you’re probably more likely to remember to take them when you first get up, and it also gets them out of the way for the day.
But in terms of how they act, taking them at night often makes a lot more sense. A Spanish study of 20,000 people with high blood pressure, published in the European Heart Journal, found that those who took their pills in the evening had almost half the risk of cardiovascular death, including heart failure and stroke, over the next six years.
It’s thought the reason for this difference is that our blood pressure rises sharply between 6am and noon as we prepare for the day. Taking antihypertensive drugs in the morning, at the same time as this rise occurs, means that their effectiveness peaks after the surge is over.
Taking them at night, on the other hand, can help reduce blood pressure as it starts to rise the following morning.
Aspirin is commonly prescribed to prevent strokes by reducing the ability of platelets to clump together and form blood clots. Foster says we make about 100 billion new platelets in the evening, so it makes sense to take aspirin then to deactivate these just as they’re being formed. That helps reduce the likelihood of having a stroke the following morning, which is when most strokes occur.
With statins, the timing of when we take them depends on whether they are short-acting (4-6 hours) or long-acting (20 -30 hours). Short-acting statins should be taken around bedtime so they are available at the same time as we start to produce higher levels of cholesterol. The timing of long-acting statins doesn’t matter as they will always overlap with higher levels of cholesterol production at night.
Foster warns that it’s important to talk to your GP before changing when you take any of these drugs. “They may not know about this, but they are capable of looking at the evidence. And I think the key thing is that we as patients need to nudge our practitioners into giving us the answers to the questions we ask.”
Getting regular
The Covid-19 lockdowns of the past two years will provide many opportunities to look at the effect that unusual changes to our daily routines have on sleep and circadian rhythms. There’s growing evidence that the lockdowns changed our sleeping patterns. For example, many people reverted to a more “natural” sleep cycle, which involves two or more periods of sleep interspersed with periods of wakefulness.
An international study, published recently in the Canadian Journal of Psychiatry, involving 997 people with mood disorders such as depression and bipolar – 521 of them from New Zealand – has found that 40% reported moderate to severe depression during our 2020 lockdown.
The researcher for the New Zealand part of the study and head of the department of psychological medicine at the University of Otago, Richard Porter, says the greater the disruption to their normal daily rhythm, the more their mood was lowered.
He says people with mood disorders are particularly susceptible to disruptions to their circadian rhythm, and while this is largely regulated by our exposure to light, social cues such as when we eat, when we exercise and when we interact with other people also play a role. “These social events help to structure our daily rhythm and have some effect on it. Aspects of social rhythm significantly changed for 80% of those in the study.”
This early finding suggests that steps need to be taken to help people with mood disorders better regulate their circadian rhythm and help prevent a drop in mood should we have any more lockdowns. In the meantime, Porter and others working in the field have put together a list of tips on how to regulate our rhythms during unpredictable times. They include:
- Setting up a routine for yourself while you are in quarantine or working from home. Routines help stabilise body clocks.
- Getting up at the same time every day. A regular wake time is the most important input for stabilising your body clock.
- Making sure you spend some time outdoors every day, especially in the early morning. Your body clock needs to “see” light in the morning to know “when” it is. If you can’t go outside, try to spend at least two hours next to a window, looking into the daylight, and focusing on being calm.
- Exercise every day, ideally at the same time each day.
- Eat meals at the same time every day. If you’re not hungry, at least eat a small snack at the prescribed time.
Where to get help:
If it’s an emergency and you feel that you or someone else is at risk, call 111.
· Need to talk? Free call or text 1737 any time for support from a trained counsellor
· Suicide Crisis Helpline – 0508 828 865 (0508 TAUTOKO)
· Lifeline – 0800 543 354 (0800 LIFELINE) or free text 4357 (HELP)
· Youthline – 0800 376 633, free text 234 or email talk@youthline.co.nz or online chat
· 0800 What’s Up - 0800 942 8787
· Samaritans – 0800 726 666
· Depression Helpline: 0800 111 757 or free text 4202 to talk to a trained counsellor, or visit depression.org.nz
· Anxiety New Zealand - 0800 269 4389 (0800 ANXIETY)
· Healthline – 0800 611 116
· Additional specialist helpline links: https://www.mentalhealth.org.nz/get-help/in-crisis/helplines/
