How the body adapts to our habits – health

The human body adapts to habits. If you drink coffee every day, you develop a tolerance. If you drive to a hot area, you will be better able to cope with the heat in the long run. But the body cannot adapt to everything: How much sleep someone needs depends, for example, on their own internal clock – and this is determined by the genes. A study from the Czech Republic has just shown that that the internal clock of many people does not match their rhythm of life. What can the body adapt to? What miracles the human body performs – and where its limits lie.

How humans adapt to heat

When it comes to its heat balance, the human body is strict. The body temperature is between about 36 and 37 degrees, the value is individually different. If the temperature rises above the normal value, the organism wants to lower it at all costs. One of the most effective methods of thermoregulation: sweating.

When you get off the plane in a hot region, your body reacts immediately: as sweat evaporates from your skin, your body cools down. If you stay in a hot climate for several days or weeks, your sweat glands will change: “You sweat more and more quickly, and you lose less salt,” explains Oliver Opatz, who works at the Center for Space Medicine and Extreme Environments at the Berlin Charité other things with thermophysiology. The blood plasma changes, small salt and water reservoirs form in the skin. And, explains Opatz: You go to the toilet less often, so reduce the amount of water you excrete. Behavior also adapts, often unconsciously. “You move more slowly, take more breaks, you sit down more often,” says Opatz. Similarly, the body also adapts to cold. For example, the threshold at which people tremble is changing.

How well someone tolerates heat or cold depends, among other things, on their weight or body fat. People with a higher body fat percentage are less able to cope with heat, but are better protected against cold. In addition, men have more sweat glands than women and also more muscle mass in relation to the body surface, so they sweat more, while women freeze faster. Over time, humans have also genetically adapted to the temperatures common in their region: people in hotter regions tend to be slimmer than average, while people in cooler latitudes are bulkier.

But humans can train to withstand heat. “We’re more adaptable than just about every other creature on the planet,” says Opatz. An example: someone has booked a trip to the Congo. To prepare the body for the heat, the physiologist advises stimulating sweat production beforehand. Going to the sauna several times or doing strenuous exercise can help. It is best to combine heat and exertion: “Then the adaptation mechanism comes into effect.”

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How the body adjusts to spicy food

Why do some people like spicy food while others don’t even understand what’s so appealing about it? How much heat someone can endure depends on their genes – but it can also be trained.

“Hot” is not a flavor; when the oral mucosa comes into contact with pungent substances, pain receptors are activated. Desensitization occurs over time. There are two possible explanations for what exactly happens in the body, says Gaby Andersen from the Leibniz Institute for Food Systems Biology at the Technical University of Munich. If someone frequently eats spicy food, at some point the ion channel called TRPV1, through which the signal “pain” reaches the brain, is either closed or internalized, i.e. moved inwards from the cell surface. The fact that the sharpness is still perceptible, albeit less intense, is due to the fact that there are many ion channels, says Andersen. And it is clear: “The desensitization can be lifted when the pungent substance is no longer there.”

In addition, a genetic aspect determines how well someone tolerates heat. The TRPV1 ion channel has a gene expression in which a specific amino acid is replaced, making the TRPV1 protein less sensitive to pungent substances. “So you perceive sharpness as not so sharp,” says Andersen. About 30 percent of people are equipped with this less sensitive variant. In East Asia, among other places, it occurs more often than on average. Maybe that’s why they like to eat spicy food there; perhaps humans in these regions have also adapted genetically to their habits.

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Can the need for sleep also be reduced?

How much sleep a person needs largely depends on their genes. About 70 percent of people are “normal sleepers”: They need seven to eight hours of sleep. For some it takes nine hours or more to feel rested, for others five hours is enough. Kneginja Richter, chief physician in the field of sleep medicine at the Curamed day clinic in Nuremberg, compares the human body with a mobile phone battery: some of them charge quickly and remain full for a long time. Others take longer to charge, but the battery drains faster.

People also differ in what time of day they are fit. There are different chronotypes. It may be that someone actually sleeps enough, but is still tired because their rhythm of life does not match their internal clock. The point in time in the sleep cycle at which you are woken up is also essential. A sleep cycle lasts about 90 minutes. In each cycle, the falling asleep phase is followed by the light sleep phase, then the deep sleep phase and finally the REM phase, also known as dream sleep. Anyone who is woken up in the middle of the deep sleep phase does not feel recovered – even if they have actually slept enough hours. Optimally, the alarm clock rings at the end of a 90-minute window, says Richter.

Now someone who sleeps nine hours has four hours less time every day than a short sleeper. Can you shake it? Over the course of life, most people actually get into the habit of sleeping less. Babies need the most sleep. Richter explains this by saying that sleeping is closely related to growth. And of course the late riser can also try to sleep less, says Richter, who conducts research at the Technical University of Nuremberg. Humans can endure a lot. “At some point, however, you collapse from exhaustion. In the long term, a lack of sleep makes you ill, as all studies have shown so far: The risk of physical illnesses increases. Humans are also becoming more susceptible to mental illnesses such as depression and burnout. Not even people who have the talent to get used to it can train their bodies to need less sleep.

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And what about coffee?

We drink something and feel awake – how does that work? The caffeine molecules use a trick to do this. They occupy receptors in the brain where adenosine actually docks, a molecule that signals to our body that we are tired. The longer someone is awake, the more adenosine accumulates; it is broken down again during sleep. However, caffeine molecules displace the adenosine and keep the receptors occupied for a while. The adenosine cannot dock and the body no longer receives signals of tiredness. However, the body has processed the caffeine at some point. Then the adenosine molecules bombard the freed receptors – and the tiredness is back.

The need for sleep cannot be reduced in this way, only the feeling of tiredness. Conversely, the body gets used to coffee. If someone drinks several cups a day, the body creates new opportunities for the adenosine. It produces additional receptors. In order to block these and feel awake, people need more coffee.

So is coffee addictive? Yes and no. According to the unanimous opinion of experts, anyone who drinks a lot of coffee and suddenly stops drinking it will feel it physically. Possible consequences are headaches, tiredness and difficulty concentrating. Nevertheless, there is a big difference to drugs like alcohol or nicotine: caffeine does not stimulate the reward center of the brain, and thus the physical compulsion to consume the substance again and again and to increase the dose is eliminated. If you don’t drink coffee for a long time, your body breaks down the additional adenosine receptors over time.