They determine how our immune system works and how we treat it. And we can use that to become healthier. We can use this to become healthier.
Take a closer look at forearm skin. Hold your hand. Maybe everything looks and feels the same as it did 12 hours ago. But if you cut or burn your arm, the skin will heal twice as fast if the damage is done by day – compared to night.
And this applies not only to the skin.
If you are planning a seasonal flu, it is best to do it in the morning – your body produces more than four times as much protective antibodies if it is between 9am and 11am, compared to six hours later.
But if you have heart surgery, then this is not the case: the chances of recovery will be much better if you lie down on the operating table in the afternoon, after twelve.
The daily rhythms that control the work of cells and tissues (called circadian rhythms) seem to dictate the speed of our recovery from infection or injury.
"We are physiologically completely different from day to night than we are at night," says Tami Martino, director of the Center for Cardiovascular Research at Guelph University in Ontario, Canada. Martino wants to find a way to apply that knowledge in medicine and veterinary medicine.
From cancer to cardiology, from arthritis to allergies – understanding how these rhythms can lead to the fact that medications and surgical interventions will only be performed at a specific time. Only the time at which they will be most effective for a particular patient and cause the least harm.
By helping these rhythms, enhancing them, we can speed up the healing process and alleviate the physical symptoms of the disease.
"From my point of view, circadian medicine can change the way we fight for human health once and for all," Martino says. "In that sense, it's in line with gene therapy, stem cells and artificial intelligence – it's one of the new promising technologies to combat the global burden of disease."
The idea that our physiology varies from hour to hour is not new at all. The famous Hippocrates observed during the day strengthening and weakening of the symptoms of the disease.
Traditional Chinese medicine describes the peaks of vitality of different organs at different times – in the lungs between 3 and 5 in the morning, in the heart between 11 and 13, in the kidneys between 17 and 19 hours and so on.
The currently renewed interest in the impact of our internal tactics on disease and treatment is linked to the increasing number of studies in this field.
By adapting our needs, behaviors and biochemistry, these rhythms prepare us for daily environmental events that dictate the daily cycle of light and darkness on our own.
When it comes to recovery, there is a good reason why it goes faster during the day than at night.
"Our cells have evolved to heal wounds more effectively at a time when they are more likely to be wounded," explains John O & # 39; Neill, a circadian biologist at the Molecular Biology Laboratory, Cambridge Medical Research Council (UK).
"If you are a human being, you are unlikely to be injured in the middle of the night while you are sleeping. But during the day, this can happen," the expert says.
His studies have shown that fibroblasts (cells that help repair damaged tissues by synthesizing intercellular substance constituents) move faster to the wound site.
"We have consistently found that during the day, the wound healed almost twice as fast," notes O & # 39; Neill.
They then analyzed pre-existing burn data and found that for those who received a burn at night, he treated about 11 days longer than for those who had it during the day.
Our immune system, its response to infection, also depends on biological rhythms.
At first glance, this addiction to the time of day may seem strange, says Rachel Edgar, a virologist at Imperial College in London. But perhaps this feature has evolved due to the need to protect us from the over-excitation of the immune system.
"If the reaction to inflammation is too strong, you will need to be able to control it – otherwise it can do you great harm," says Edgar, who explores the relationship between circadian rhythms and herpes-like viral infections.
During one of the experiments, she found that if mice become infected at the onset of hibernation (since mice are nocturnal animals, this is obtained in the early morning), the herpes virus multiplies ten times more intensely than when the mice are infected at the beginning of the active phase.
All this suggests that it is not just about changing the activity of the immune system. The daily rhythms of infected cells also affect the extent of infection with the virus.
This is also indicated by the results of a recent human study: the response to the flu shot was stronger if given in the morning (compared to the day).
That's true, but to say that there is one optimal time to get sick would be a simplification, Edgar warns.
"For different infections, the weather will be different," she says. For example, take sepsis, a powerful and life-threatening response to infection. It can be triggered by the introduction of molecules collected on the surface of bacteria into the blood.
If you do this to mice during their "night", only 20% of them will survive. If done in the period of their activity, then they will survive more than 90%.
The results of these studies open up exciting new prospects for the treatment of infectious diseases.
"If we know that a virus spreads to neighboring cells at a certain time, then we could only use antiviral drugs when they are most effective," Edgar says.
"It would reduce the amount of medication needed and make it easier for patients."
But these are not all advantages. More than half of the drugs that WHO includes in the list of essential drugs (250 drugs that should be in any hospital in the world) encounter the behavior of molecules subject to the internal clock of body cells. That way, they can be more or less effective if taken at different times of the day.
Among these drugs are common painkillers such as ibuprofen and aspirin, as well as blood pressure regulators, peptic ulcer drugs, asthma and cancer.
In many cases, the half-life of these drugs is less than six hours, that is, they do not stay in the body long enough to find the optimal time if taken as "unsuccessful".
For example, valsartan, a popular hypertension drug, is 60% more effective if taken in the evening rather than in the morning. Aspirin is also more effective in the evening, like many allergy antihistamines.
A recent study found that radiation can be more effective if performed in the afternoon rather than in the morning.
However, everything is not as simple as it seems. The cost of clinical trials, if we decide to launch a systematic study of drugs at the exact time of their administration, will be invaluable.
The problem will also be how to convince patients to take their medication at the best hours for it.
O & # 39; Neill and other scientists doubt that these are the main reasons why pharmaceutical companies, despite their clear interest in so-called chronotherapy, are in no hurry to do so.
Circadian rhythms are different for everyone. Someone an early bird, someone an owl. A significant proportion of people work at night, which can affect their biorhythms and general health.
And they still haven't figured out how to quickly and easily check the exact location of your internal clock's hands in a specific minute.
Hospitals are also a problem. Many modern buildings have small windows and artificial lighting is switched on day and night, which adversely affects patients' sleep and their biorhythm.
Interrupted or worn rhythms are common among hospital patients.
To aggravate the problem, certain drugs – for example, morphine – can also alter the course of the circadian clock, not to mention that pain, anxiety and noise affect the patient's healthy sleep (necessary for faster recovery). One wonders how much this impedes not only the recovery but also the survival of the patients.
This seems most convincing in the case of patients with heart disease. As with other systems, the tissues of the cardiovascular system are subject to a clear circadian rhythm.
Heart rate and blood pressure decrease when we sleep, but increase suddenly when we wake up. Our platelets (small blood platelets that play, among other things, a crucial role in healing and regenerating damaged tissues) are more "sticky" throughout the day. And the levels of hormones such as adrenaline, which compress our blood vessels and make our heart beat faster, are also higher in the afternoon.
These circadian variations affect the time at which serious disorders in the cardiovascular system, such as heart attacks, occur.
"If you watch people go to the hospital with a heart attack, you will see that it usually happens to them between 6am and noon," says Martino. The time of the attack can also affect the speed of recovery from a heart attack.
One recent study found that for those who underwent heart valve replacement surgery, the likelihood of having a severe heart attack over the next 500 days depends on the time of day the surgery was performed. If the operation is performed during the day, the risk is halved (compared to morning surgery).
As the researchers calculated, if surgery was always performed throughout the day, it would avoid one serious complication in every 11th patient.
From other studies, it became clear that those patients who spent more time in daylight had a better chance of surviving after cardiac surgery and early discharge from hospital.
Animal experiments help to understand why this is so. When Martino and her colleagues conducted studies in mice simulating heart attacks, it turned out that in daylight a much larger number of certain types of immune cells were mobilized, the tissue eventually healing faster.
Those mice whose circadian rhythms were impaired (as in some hospital patients) were more likely to die of heart necrosis.
Further studies found a difference in the type and number of immune cells that attack damaged heart tissue – depending on the time of day when the heart attack occurred.
"In some intensive care units, the lighting is dimmed at night, but it's not everywhere," Martino says. "For example, if people go to a hospital with a heart attack or stroke and there is no room in the wards, they have to spend the night in the hall, in bright light."
"Their sleep is disturbed, circadian rhythms are stopping – and this is what happens in the early days, which is so important to the further course of healing."
What to do? One solution is to prescribe surgeries for those hours when the body is at its best.
It may be given for cardiac surgery, but the time for other surgical interventions may vary.
For example, O & # 39; Neill, examining how wounds heal, found that a larger scar is created during the day due to the production of more collagen.
"From a cosmetic surgery point of view, this is an argument for surgery in the evening. It will heal longer, but the scars will not be as noticeable," he muses, noting, however, that no one has checked it yet.
Another solution is to install circadian lighting systems that vary in strength depending on the time of day, simulating natural light.
At Copenhagen's Gloustrup Hospital, doctors measure the effect of such a system in the post-stroke rehabilitation department. So far, the data suggests that patients there have reduced levels of anxiety and depression and a more stable circadian rhythm than those in the normal-light ward.
It is even possible to create drugs that can stabilize circadian rhythm in hospital patients – or suspend them long enough to perform surgery at optimal hours for subsequent recovery. Such molecules are already being tested on animals, and the results are encouraging.
"I predict that in the future we will use circadian tablets and treat heart disease without the absence or presence of light," says Martino.
Light, sleep, and the right time – we often take it for granted, but these three most basic things can reshape healthcare.
Linda Geddes is a British journalist and writer, author of the popular science book, After the Sun.
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