About water and physical education
To drink or not to drink
How much water should we drink every day to be healthy? Can drinking water rejuvenate us and is there any scientific evidence for this? What is the optimal daily exercise load for a person? We understand these issues together with the nutritionist Elena Motova.
– "Is there such an amount of water that each of us should drink every day?" – that's the question I'm constantly being asked. And there are norms of average water consumption, as well as the "average temperature in the hospital" – they will say little about a particular person. Life is much more interesting.
For example, in 1976, anthropologist Claude Pak found that, surprisingly, nomads, inhabitants of the Sahara desert, drink much less water than they need. And a dermatologist at the Hebrew University in Jerusalem, Ronnie Wolf, together with his colleagues, collected all the research on this topic. But there is no scientific evidence that excessive water consumption can rejuvenate you, make your skin more hydrated, somehow slow down aging. Alas and ah! – there is nothing like that.
How much we drink and how much we excrete – this water-electrolyte balance is in balance. Status quo is provided by several feedback systems at once. That is, when we lose water, the substances dissolved in it become too concentrated. This is picked up by special receptors that are located in the vessels and in the intercellular fluid, and send signals to the hypothalamus, where the thirst center is located. At the same time, the hypothalamus synthesizes, and the pituitary gland secretes the hormone vasopressin, and there is an increase in the reverse absorption of water in the kidneys. That is, the water returns to the cells. Thus, it turns out that healthy kidneys can vary the amount of urine released from 0.5 to 2.5 liters.
But all the same, the liquid is lost, and it needs to be replenished somehow. There is a thirst mechanism for this. It is also controlled by the thirst center in the hypothalamus. That is, when we lose water, we want to drink. Thirst is stimulated by the dryness of the mucous membranes. That is why water causes instant relief, even before it has been absorbed in the stomach and entered the cell. If it were not for this mechanism, we would drink much more liquid, but we simply do not need to overuse.
Excess water with a deficiency of salts can cause even such a dangerous condition as water intoxication. Do not forget about it. Yes, we have recommendations for infusion therapy, where the amount of fluid is calculated according to the formula 25-30 ml per kg, but this is necessary if a person cannot eat and drink normally. Because we get water from water and from food too. These are very rare situations when this is not possible – for example, when a person is preparing for surgery. Maybe it's different for bottled water producers. They are just really fussing with this figure. I don't know anything about them.
Thus, we have mechanisms that return water to the cells. We have thirst. And for healthy adults, "waterboarding" is canceled – it's enough to drink as much as you want. That is, just drink when you want. There are situations when additional water consumption is needed – for example, with constipation, with urolithiasis, we recommend it. But there are also situations when excess water is not recommended. In some elderly people, this mechanism of thirst may be slightly disrupted. And they just have to make sure they drink enough. It is easier to do this if you monitor the color of urine. It shouldn't be very dark. It should be straw yellow. Such a control measure is rather an exception. For everyone else, you can follow the thirst signals.
What is the optimal daily exercise load for a person?
How to be physically active correctly? This is also very important. To do this, we have global recommendations on physical activity for health of the World Health Organization (WHO). Adults should exercise 150 minutes a week. These are moderate intensity aerobic exercises. Or you can have 75 minutes of high intensity. You will get additional benefits if you increase this time to 300 and 150 minutes, respectively.
You can break up your classes into ten-minute excerpts. That is, it's not necessarily just all at once. In addition, you can add strength training to the main muscle groups two or more times a week. The intensity of the class is determined by how much the heart needs to supply more oxygen and nutrients with blood during your classes. It is defined as a percentage of the maximum number of heartbeats.
The maximum frequency can be calculated using a very simple formula; it is clear that it will be approximately 220 minus age. And 60-70% of the maximum heart rate is moderate loads. For example, this is fast walking, that is, 100 steps per minute or five or more km/ h. This is water aerobics or walking cycling. Intensive load is 70-85% of the maximum heart rate. This is running, rowing, sports dancing. You can accurately calculate your maximum heart rate using the increasing load on the bicycle ergometer under the control of an electrocardiogram (ECG).
In principle, this is not necessary in ordinary life. For example, a conversational test is enough. That is, if the load is moderate, then you will be able to talk. If it is intense, then it will be practically impossible. In addition, if the load is intense, you will sweat almost immediately. It can be used to monitor the heart rate, such a device as a heart rate monitor.
In principle, the recommendations on physical activity of the American Association of Sports Medicine are very close to what the WHO gives. This is again five to seven days a week - 30 or more minutes of aerobic exercise, two or three times a week – power loads on the main muscle groups. There must be intervals of one or two days between them. And these are also loads that help us maintain flexibility (what is called "stretching"). You have to remember that it shouldn't hurt. You may feel tension, slight discomfort, but there should be no pain.
It is very important that the loads correspond to your level of fitness, increase gradually and be sure to give you pleasure. In principle, we understand very well what happens to the body during physical activity. The heart and lungs should increase the supply of oxygen and nutrients to the muscles, so breathing becomes faster and deeper. It turns out that with one, each heartbeat, more blood comes in, and the cardiac output increases (that is, the amount of blood that is supplied per minute). Thus, cardio-respiratory endurance improves gradually when you exercise, that is, the maximum amount of oxygen that the cardiovascular system supplies to the working muscles. It is clear that the vessels relax, peripheral resistance decreases. This means that at rest the blood pressure will be lower.
These are the physiological bonuses from activity. It is now very well studied how activity in principle affects health. This is again observational cohort studies, where we do not change people's lives, but simply observe how active they are. We record their other habits, morbidity, mortality, and within the framework of one study, two similar cohorts with different activity can be identified and then simply compare them with each other.
The first such study began already in 1948. Now, of course, there are much more of them. You can analyze them together or separately. Now we understand that physical activity reduces the risk of general and cardiac mortality, reduces the risks of diabetes and many diseases in general.
In fact, of course, we would like a large randomized study of physical activity – just to better understand cause-and-effect relationships, which is very important in science (medicine). However, in principle, what we know now is already enough to understand: an active life is better than a sedentary one.
In this regard, I remember my patient, a very elderly woman, who just dragged a wooden pallet to her home, on which you can walk. She steps up and down while watching TV shows. Everyone can be physically active enough if they want to, which is what I am calling you to do.
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