The discipline that studies the relationship between time and the biological rhythms of people is called chronobiology. Specialists point out that knowing the biological schedule of an individual allows, just to mention a few examples, that the patient responds better to a medication, to exercise or to the absorption of a certain nutrient. Although each person has their own habits, and they must be studied individually, in all cases the passing of the hours of the day (24 hour circadian rhythm) generates changes in the various mechanisms that the body has to regulate its functioning.
Fernando Botto, cardiologist in chief of the research area of the Cardiovascular Institute of Buenos Aires, explains that circadian rhythms compromise all the mechanisms that the organism has organized to survive in its healthy functioning. “When we sleep, we accumulate glucose, triglycerides and nutrients in the tissues. And when we wake up, the body starts up and, among other things, increases the pressure and heart rate. Circadian rhythms are governed by the brain with the autonomic nervous system, which is what opens the pupils or generates saliva, for example. That is, we do not control it,” says Botto.
The study of chronobiology, according to doctor Daniel Cardinali, professor emeritus at the University of Buenos Aires, is of vital importance. Knowing the biological schedule of each individual, he says, makes it possible to understand the specific moment in which he can best respond to a treatment, such as a cancer therapyor determine when the toxicity of a drug can be minimized and its efficacy increased.
We’ve put together a guide on how circadian rhythms impact the heart, the brain and food. Although specialists emphasize that, although general recommendations can be given, it is convenient that each case be analyzed in a particular way.
In the morning
When a person wakes up, Botto describes, there is usually an increase in blood pressure and heart rate. “That’s because the autonomic nervous system releases chemicals like cortisol and adrenaline. It also increases the level of glucose and insulin in the blood. This activation is physiological and depends on the ‘internal clocks’ that prepare the body to start the day, but for vulnerable people, with poorly controlled risk factors (for example, high cholesterol, high blood pressure, overweight), it is a propitious scenario to suffer a heart attack or stroke. Therefore, the highest incidence of heart attacks occurs between six and ten in the morning. When it is said that someone died sleeping, it is possible that they woke up at dawn and that the physical reaction generated by waking up has collaborated in the death.
As for exercise, although it is advisable to do it at any time of the day, Botto affirms that it is optimal to train in the morning. “Aerobic exercise is healthy at all times, but it seems that in the morning it adapts better to internal rhythms, since many metabolic mechanisms to produce energy. The cardiovascular benefits would be greater. Similarly, it would be better to consume the most calories in the morning and not at night, as is customary.”
In case of controlled pressure, Botto recommends that it not be taken at the same time of day. The test should be performed when the person feels well because, he clarifies, it is one thing to be hypertensive and it is quite another to have a circumstantial event of high blood pressure caused by some bodily ailment, worry or stress, which should not be taken as real hypertension.
Regarding the time to take antihypertensives, the expert indicates that some specialists recommend using them in the morning so that the drug has its peak of action at the time of greatest cardiovascular risk. However, Botto points out that there is debate about this and there is no definite recommendation. Each doctor decides with his patient, in a personalized way.
At night, the pressure should drop between 10 and 20 percent. If it doesn’t, it’s an example of a circadian rhythm disturbance, which increases the risk of a heart attack.
In relation to the brain, Pablo López, a member of Ineco’s Cognitive Psychotherapy department, explains that its cycles are broader and are divided into sleep and wakefulness. They are within the aforementioned circadian rhythms and that is why it is said that sleep is regulated by a biological clock. At the brain level, this clock is located in an area called the suprachiasmatic nucleus (SCN) and sends signals to other brain structures associated with sleep regulation, indicating and differentiating the moments in which the predisposition to sleep increases or decreases. To do this, the hypothalamus, the structure where the SCN is located, sends signals to stimulate or inhibit melatonin production.
“At the environmental level, the previously described circuit is regulated by the presence and absence of light. In this sense, the lack of light predisposes us to sleep because, among other things, it increases the production of melatonin. On the other hand, in the morning hours the opposite process occurs: the melatonin and cortisol and glucose rise, associated with energy and activity, making it easier to wake up,” adds López.
Regarding sexual energy, Cardinali describes that “the variability of sexual desire in men is linked to testosterone levels, whose peak occurs in the second half of sleep. Therefore, the morning should be the time of greatest sexual desire. In the case of women, libido is linked to another chronobiological aspect, which are not the hours of the day, but the menstrual cycle. The desire grows in the periovulatory stage (half of the menstrual cycle) and in the premenstrual moment.
Regarding nutrition, Mónica Katz –founder of the Eating Disorders Team at the Hospital Durand and author of the book The non-diet method– believes that the science of nutrition could generate new ways of addressing metabolic health and obesity through the implementation of dietary guidelines directed at meal times.
Eating breakfast, he says, is accepted as beneficial, despite the fact that many people do so-called intermittent fasting. According to Katz, breakfast can boost energy, focus, memory, and problem-solving skills.
It also improves metabolism, digestion, and bone strength, and helps lower the risk of heart disease, high blood pressure, and obesity. “A recent meta-analysis showed an association between energy intake at night and higher average body mass index. People with obesity consume most of their calories in the afternoon and evening period, compared to thin people. Calorie intake in the morning resulted in 5.1 kg greater weight loss relative to calorie intake at night. Also, higher caloric intake in the morning increases satiety, improves blood glucose, insulin, triglycerides, and decreases hunger,” she says.
On the other hand, on whether or not there is breakfast, there are those who defend intermittent fasting. “In my experience,” adds Katz, “intermittent fasting is safe for some. For others, especially with a history of Eating Disorders and altered body image, can represent a dangerous path towards unhealthy patterns of restrictive eating.
In the afternoon
López points out that there is another ‘milestone’ during the sleep-wake cycle that usually occurs around 2 in the afternoon. “It is usual that at that time we notice that sleep also increases. This does not have to do only with the fact of having eaten or not, but with the fall of the mechanisms in charge of maintaining alertness. In this sense, the process of the circadian rhythm coexists with the process involved in digestion, through which information reaches the Central Nervous System from the digestive tract and through the vagus nerve, which inhibits the alert mechanisms of our body”.
Studies indicate that those who work at night, even sleeping the recommended hours, do not recover in the same way as those who sleep at night.
When is there a greater brain predisposition to learn and create? One of the aspects to take into account when referring to the level of activity is that of the chronotypes, which can be defined as the predisposition of each person to have peaks of energy and rest. “There are people who usually prefer the morning schedules (morning chronotype or larks) and others the night hours (late chronotype, commonly called owls). However, most do not fall into either of these two extremes and have an intermediate chronotype,” says López.
Regarding the heart, in the afternoons the fall of the morning action begins. Lowers heart rate and blood pressure. The so-called anabolism begins, which is the process by which they begin to generate fat deposits. None of this implies, Botto warns, that there are no heart attacks in the afternoon, but the percentage is usually lower than in the morning.
Katz, for his part, points out that it has not been studied that a person should wait a certain number of hours after lunch to eat again. “But it is appropriate, compulsive people with a history of memory of hunger, who eat more frequently. Everything will depend on the individual eating behavior profile”.
At night
“Overnight, the pressure should drop by 10 to 20 percent. If it doesn’t, it’s an example of a circadian rhythm disturbance. When for some reason these rhythms are altered, the risk of a heart attack. For this reason, people who work at night may have a greater tendency to diabetes, obesity, cognitive disorders and cardiovascular risk”, explains Botto.
How many hours are you suppose to sleep? In the case of adults, the recommendation is to sleep between 6 and 8 hours a day. However, there is great variability between people with respect to hours they need to sleep. One aspect that influences is the stability of the schedule. Sleeping eight hours on a regular schedule is not the same as sleeping the same hours at different times of the day.
“Our body is designed to sleep at night and be awake during the day. However, for different reasons, some people are awake at night and sleep during the day. These people require extra effort to stay awake during activity by going contrary to our physiology. Some studies even indicate that those who work at night, even sleeping the recommended hours, do not recover in the same way as those who sleep at night,” says López.
As for nighttime eating, Katz says that “night workers are predisposed to weight gain and metabolic disturbances. Although there is no specific time, the data points At 7 pm as the optimal healthy limit. Which is related to the biological clock.
ALEJANDRO HORVAT
The Nation (Argentina) GDA