- Body clock in our brain is the master timer that regulates when we sleep
- Even our libido is subject to the forces of an internal clock
- If you suffer with a bad back and find it’s worse in mornings, it could be due to spine ‘clock’
The fact we have a body clock that determines when we feel sleepy or alert is well known — and most people, if pushed, would guess it’s in our brain.
But did you know you also have a ‘clock’ in your spine? In fact, scientists have discovered clocks (or circadian rhythms) in other organs, from the liver to skin.
‘Our body clocks regulate almost every aspect of health and wellness,’ says Professor Satchidananda Panda of the Salk Institute in California and one of the world’s leading experts in chronobiology — the study of body clocks.
Understanding how our many body clocks work could, for example, determine the best time to take certain medication. So what are the clocks, and what effect do they have?
The body clock in our brain is the master clock that regulates, among other things, when we wake up and when we fall asleep
BRAIN CLOCK UPSET BY WEEKEND LIE-INS
The body clock in our brain is the master clock that regulates, among other things, when we wake up and when we fall asleep.
This ‘clock’ is a cluster of about 50,000 nerve cells in the hypothalamus, an area roughly the size of a cherry behind the eyes.
Known as the suprachiasmatic nuclei, or SCN, this central clock is set by daylight hitting the back of the eye in the morning.
This signals to the SCN when to release hormones such as cortisol and adrenaline, which speed up the body and promote wakefulness, and melatonin, which slows it down ready for sleep.
The SCN governs clocks in other organs, telling them when to turn on key activities.
‘These clocks stop processes such as the release of hormones, the processing of food and the release of energy in the blood happening at the same time and make sure they take place in the right order,’ says Russell Foster, a professor of circadian neuroscience at Oxford University.
Our body clocks are disrupted by erratic sleep habits and eating at random times of the day and night.
‘Paying attention to when and how much we sleep or when we eat can maintain a healthy clock and prevent diseases such as diabetes and obesity,’ says Professor Panda.
In terms of our wake/sleep cycle, that’s why it’s important to get up and go to bed at the same time — and explains why a lie-in on the weekend may affect the quality of your sleep and freshness on a Monday.
Similarly, turning on the bathroom or bedroom lights when you wake up in the night can disrupt healthy sleep.
WOMEN PRIMED FOR SEX AT 10PM
Even our libido is subject to the forces of an internal clock. Overnight, the levels of testosterone, the main sex hormone that governs sex drive in men, rise.
‘When a man wakes up his levels of testosterone are about 25 per cent higher than later in the day,’ says Ashley Grossman, a professor of endocrinology at Oxford University.
Anthropologists believe this surge is timed to co-ordinate with sunrise. Testosterone would have driven our caveman ancestors to get up, catch food and fight off attackers.
Even our libido is subject to the forces of an internal clock. Overnight, the levels of testosterone, the main sex hormone that governs sex drive in men, rise
Testosterone is produced in response to a pulse in the pituitary gland in the brain.
‘However, it stays in the blood a fairly long time, so after the high levels in the morning, there is not much variation in levels during the day,’ says Professor Grossman.
By contrast, woman’s sex hormones such as oestrogen are at their lowest when they wake up — and rise gradually through the day.
By 10pm, levels of testosterone in men are at their lowest while a woman’s sex hormones are peaking, but because men have much higher levels than women to begin with, their levels are now matched enough for this to be the time of day when most couples have sex.
‘Even though male testosterone may have dipped, their levels are running as high as a woman’s, so men are still responsive,’ says Gabrielle Downey, a consultant gynaecologist at Sandwell and West Brimingham Hospitals NHS Trust and BMI Healthcare.
Cells in the discs between the vertebrae have their own clocks and a new study published last month found that these — under instruction from the SCN — make a protein called cryptochrome while we sleep
BACK PAIN TURNS OFF AT NIGHT
If you suffer with a bad back and find that it is worse in the mornings, it could be due to the ‘clock’ in the spine.
Cells in the discs between the vertebrae have their own clocks and a new study published last month found that these — under instruction from the SCN — make a protein called cryptochrome while we sleep.
This protein appears to dampen down inflammation in the discs.
But it wears off as morning approaches, which is why stiffness and pain return, according to the study published in the journal Federation of American Societies for Experimental Biology.
So regularly getting a good night’s sleep may help ease back pain, says Dr Qing-Jun Meng, a chronobiology expert at Manchester University.
‘In future, it might also have implications for when we take pain relief medication.’
SKIN LOOKS BEST IN THE MORNING
There’s a reason our skin has more of a natural glow in the morning. Professor Panda has found there is a strong circadian rhythm in skin and hair.
‘If you take mice and in the morning give them radiation therapy, they lose 85 per cent of their hair,’ he says. ‘If you give the same radiation in the evening, they keep 85 per cent of their hair because the hair and skin repair mechanism is much stronger in the evening.’
Similar timings appear to happen in humans. During deep sleep, the growth hormone DHEA — produced by the adrenal glands above the kidneys — triggers skin cells to start replicating themselves.
Professor Panda says that in the future, it might mean cancer patients could be given radiation in the evening so they suffer less skin damage.
EATING LATE MAKES YOU FAT
When you go to bed, your digestive system sleeps too, thanks to a mixture of messages from SCN and other factors, such as the lack of gastric acid because no food is entering the body.
With no food coming in, the liver switches from burning sugar for energy to burning the fats it has stored during the day.
When you go to bed, your digestive system sleeps too, thanks to a mixture of messages
But if this cycle is disrupted by eating close to bedtime, reawakening the digestive system, the liver is forced to a go back to storing fat instead of burning it, which can lead to weight gain.
This means midnight snacking may be even worse than previously suspected, according to Professor Panda. Indeed, avoiding all food between 7pm and 6am helps people lose almost a pound a fortnight, according to 2013 research at Brigham Young University in Utah.
Professor Panda adds: ‘So if you don’t want to gain weight, it’s best not to eat late at night and if possible try and go for 12 hours without eating overnight to allow the liver to do its job.’
VIRUS ATTACK IN THE EVENING
Our immune system also runs to a timer, and new research has found it may be easier to catch viruses at the start of the day than the end.
When researchers infected mice with a herpes virus at different times of the day for a study last month in the Proceedings of the National Academy of Sciences, the virus multiplied ten times as quickly in animals given it at sunrise compared with those infected later in the day.
‘Since our cells are miniature factories, making things that the virus must have to copy itself, the virus is less likely to succeed when the cells’ production lines are shut down,’ says Professor Akhilesh Reddy, a neuroscientist at the department of clinical neuroscience at Cambridge University.
‘Just before dusk the cell is winding down. If a virus comes along then, it will not have a favourable environment to copy itself. But if the viruses hit the cells in the morning, they have everything they need.’
This may mean it’s most useful to take anti-viral medicines in the morning, though more research is needed.
EYES HATE BRIGHT LIGHT AT NIGHT
Light passing through the eye is one of the main ways the body sets the time for the day. But as well as sending messages to the body clock of the brain, the eyes have their own internal body timings.
When it is daylight, we use more of the photoreceptors at the back of eyes that allow us to see colour in bright light. At night, we make more use of different receptors that help us see in lower light, but do not allow colour vision.
While electricity extends the hours of light, the eye has evolved to expect darkness when the sun goes down. So in the evenings, our eyes don’t respond as well to light as they do during the day, says Stuart Peirson, an associate professor of neuroscience at Oxford University.
In particular the switch between the different receptors may make it harder to see contrasts between light and dark at night during activities such as driving, so it’s wise to allow your eyes to adjust.
This switch between the different types of photoceptors is driven by a clock found in the retina.
Levels of the stress hormone adrenaline, which is produced by the adrenal glands and keeps the airways open, peak mid-afternoon, making breathing easier
RISK OF ASTHMA IN EARLY HOURS
Levels of the stress hormone adrenaline, which is produced by the adrenal glands and keeps the airways open, peak mid-afternoon, making breathing easier.
The levels drop during the night to allow us to sleep — but this makes the airways constrict, which is why asthma attacks are more common at night.
This is compounded by the fact the hormone cortisol, also released by the adrenal glands, peaks in the early morning, and drops during the night to allow us to sleep.
Cortisol dampens the immune response and inflammation so the drop in levels also makes asthma attacks more likely in the night.
Research by the National Jewish Center for Immunology and Respiratory Medicine in Denver found asthma symptoms were worse between 10pm and 7am, peaking between 2am and 4am.
‘Allergies such as asthma are an immune response and our immune systems may have evolved to work harder when in the past we were hunkering down with others who may have had infections and diseases,’ says Professor Foster.
He suggests it may help asthma patients to take medication when it is needed most: ‘last thing at night’.
MORNINGS BAD FOR HEART ATTACKS
When we sleep, our heart beats at its slowest from 2am to 4am — ten to 30 beats a minute lower than our average daytime rate because we do not need as much blood circulating.
But before we stir, the SCN sends signals to the adrenal glands to raise levels of waking-up hormones, such as cortisol, and your heart rate starts to rise. This dawn kick-start means the morning is also the most likely time for heart attacks — because small clots may have formed during the night and when blood pressure rises in the morning, these may then move.
‘Studies have shown there is a 49 per cent greater chance of having a stroke or heart attack at this time of the day,’ says Professor Foster.
In the evening, the SCN will kick in again, dropping cortisol levels and preparing the body for sleep.
Professor Panda has developed an app to help you understand your body clock rhythms: mycircadian clock.org
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Tags: back pain, body clock, body clock in our brain, chronobiology, circadian rhythms, Dalai Lama, Dr Constantinos Kyriakides, endocrinology, internal clock, libido, medication, NHS, overweight, Oxford University, Professor Satchidananda Panda, Salk Institute, SCN, sex, sex drive, sex hormone, study of body clocks, testosterone, vertebrae, weight gain, when we wake up and when we fall asleep