How Circadian Rhythms, Sleep, and the Endocrine System Are Connected
circadian rhythms – These are cyclic changes in biological processes in the body associated with the change of day and night. This is how our planet is arranged – the Earth, revolving around the sun, causes daily fluctuations in illumination. All living beings — bacteria, fungi, animals, people — had to adapt to this feature of the Earth.
The work of circadian rhythms support cellular internal clock – genes that affect not just any one trait, but the behavior of the whole organism. The main driver of circadian rhythms in mammals is suprachiasmatic nucleus of the hypothalamus (SHG). It receives information from light-sensitive cells of the retina and other receptors regarding external light signals. At night, the SHG gives the command pineal gland produce the hormone melatonin. When morning comes and light levels increase, melatonin secretion decreases. Thus, the sleep-wake rhythm is formed.
Per day for an adult produced regarding 30 mcg of melatonin, but at night its concentration is ten times higher than during the day. With a reduction in the duration of sleep, melatonin production at night decreases significantly and approaches daytime levels. This hormone plays a huge role in the life of the body. Melatonin boosts immunity, acts as an antioxidant and fights oxidative processes in the body caused by free radicals.
It also affects the functioning of the endocrine system. Melatonin informs information regarding the rhythms generated in the SCN to other organs, including the endocrine glands.
Normally, the cyclicity of all processes in the body, including the production of hormones, conjugated with the sleep-wake rhythm. In people with sleep deprivation and disorders, this rhythm is disturbed, which leads to malfunction of the endocrine glands, abnormal hormone levels and the development of endocrinopathies.
Lack of sleep is one of the causes of obesity
TRAIN called Obesity is the main threat to human health in 2022. According to the organization, more than 1.9 billion adults in the world are overweight. Of these, regarding 650 million are obese. The situation with childhood obesity is no better: in the European region, one in three children aged 6–9 It has overweight or obesity. Scientists suggest that one of the reasons for global obesity rates is the high prevalence of lack of sleep.
The less a person sleeps, the faster he gains weight. Clinical researches showthat sleep duration of 5 hours or less per day increases the likelihood of developing obesity in men by 3.7 times, in women by 2.3 times.
Lack of sleep promotes development and childhood obesity. Eleven cohort studies conducted among children and adolescents found a significant association between sleep deprivation and weight gain.
Sleep deprivation increases the risk of obesity in children more than in adults. Children’s bodies are very sensitive to lack of sleep. Scientists suggest that sleep deprivation may alter the functioning of the hypothalamus in children, which regulates eating behavior and energy expenditure.
There are mechanisms that explain the link between lack of sleep and obesity:
- Lack of sleep interferes with synthesis leptin and ghrelin. Leptin is produced by adipose tissue and is responsible for suppressing appetite. Ghrelin is synthesized in the gastrointestinal tract and is aimed at stimulating appetite. Clinical studies show that sleep deprivation significantly decreases leptin levels and increases ghrelin levels. This leads to a constant feeling of hunger and increased appetite. A person begins to eat more often and gains weight. In addition, increased ghrelin production increases cravings for high-calorie foods, which also increases the risk of obesity.
- It also disrupts the production somatotropin (growth hormone), which promotes the breakdown of fat and an increase in the ratio of muscle mass to fat. Growth hormone is produced by the pituitary gland around the clock, but its highest concentration occurs at night. With sleep deprivation, the synthesis of growth hormone is sharply reduced. This leads to the accumulation of fat in the body with a simultaneous decrease in muscle mass.
- Lack of sleep contributes to a sedentary lifestyle. American scientists at Cleveland University Hospital conducted A 16-year study of over 68,000 nurses. Every two years, using a questionnaire, scientists tracked sleep duration, weight, physical activity and other indicators. After the study ended, data analysis showed an inverse relationship between sleep duration and weight gain. One of the reasons was low physical activity. If a person does not get enough sleep regularly, then he lacks the strength and motivation to lead an active lifestyle. With a lack of sleep, two desires dominate: to eat and to lie down.
Some sleep disorders make it difficult to lose weight. At the National Medical Research Center of Endocrinology was carried out study of 200 obese people enrolled in a weight loss program. Insomnia (insomnia) was detected in 17% of the subjects, in a third – obstructive sleep apnea (SOAS). A quarter of patients had both diseases.
Insomnia leads to mental disorders, increased anxiety, emotional overeating, frequent evening and night snacks. All this reduces the effectiveness of obesity treatment.
Sleep apnea had no effect on mental health, eating behavior, or the effectiveness of obesity treatment. But patients with this disease had various endocrine disorders:
- low testosterone levels in men;
- low levels of IGF-1 – a hormone that stimulates the growth of bones and tissues, contributes to an increase in muscle mass;
- high insulin levels between meals;
- high concentration of cortisol in the night urine.
Sleep disorders and DM 2
Type 2 diabetes mellitus (DM 2) is another scourge of our time. According to WHO, type 2 diabetes suffering almost 250 million people in the world, and by 2025 their number will increase by 1.5 times.
Meta-analysis of 36 studies showedthat sleep disturbances are just as strong a trigger for type 2 diabetes as traditional risk factors, which include overweight, heredity, and a sedentary lifestyle.
The determinant of DM 2 is obstructive sleep apnea. Clinical researches demonstratethat 15–40% of people with OSAS develop diabetes over time. And the more pronounced a person’s breathing disorders during sleep, the higher the likelihood of type 2 diabetes.
One of the mechanisms by which OSAS leads to diabetes is sleep fragmentation. Due to regular pauses in breathing at night, sleep is broken into pieces. As a result, a person does not go through all stages of sleep and does not receive the right amount slow sleep.
During sleep fragmentation, the number of macrophages in adipose tissue increases and other processes are observed that are characteristic of oxidative stress, in which cells are destroyed under the influence of reactive oxygen species (free radicals). Oxidative stress leads to insulin resistancewhich, in turn, contributes to the development of type 2 diabetes.
Increases the risk of developing type 2 diabetes and sleep deprivation. With short sleep, the risk of obesity increases, and obesity is one of the main causes of the development of type 2 diabetes. In addition, with a lack of sleep, the level inflammatory cytokinesactivated sympathetic nervous systemwhich negatively affects metabolism.
Sleep disorders and metabolic syndrome
metabolic syndrome (MS) is a chronic metabolic disorder, which is accompanied by the development of several pathological conditions. Its leading clinical sign is abdominal obesity. Additional diagnostic criteria:
- arterial hypertension;
- high amount of triglycerides in the blood;
- low levels of “good” cholesterol;
- elevated blood sugar on an empty stomach and / or two hours following a meal.
The diagnosis of MS is established in the presence of abdominal obesity and two or more additional features.
According to the INTERHEART study, more than a quarter of adults in the world suffer from metabolic syndrome. In Russia, 40% of the population has two diagnostic signs of MS, 11% – three or more signs. Metabolic syndrome is detected in every second person with obesity and in 80% of people with type 2 diabetes.
Clinical researches show: the risk of developing metabolic syndrome in people with normal sleep duration is lower than in those who sleep little. At the same time, too much sleep also increases the risk of developing the disease.
Scientists suggestthat prolonged sleep reduces energy expenditure, which is associated with obesity and its consequences, which include metabolic syndrome.
Exists link between social jet lag and metabolic syndrome. social jetlag – a mismatch of the human circadian rhythm with the natural daily rhythm, caused by a work or study schedule. It is similar to jetlag that occurs following a long flight, but is not associated with the difference in time in different parts of the Earth, but with the mismatch of biological clocks with social requirements. Clinical studies demonstrate that social jet lag lasting ≥ 2 hours increases the risk of developing metabolic syndrome, as well as prediabetes and diabetes.
Shift work negatively affects metabolism, which often leads to the fact that a person sleeps during the day and eats at night. At night, leptin levels decrease, so appetite increases. This leads to overeating, weight gain, and then to impaired glucose tolerance, insulin resistance.
Many cross-sectional studies show a significant association between insomnia and MS. This relationship persists even with normal sleep duration. Insomnia leads to a violation of glycemia, a decrease in the level of “good” cholesterol, and an increased content of triglycerides in the blood. All this contributes to the development of metabolic syndrome.
How to improve sleep and reduce the risk of endocrinopathies
Restoring normal sleep allows you to improve eating behavior, reduce the risk of obesity and other endocrinopathies. You can get rid of sleep disorders not only with the help of drug therapy, which often leads to side effects. There is a safer way – compliance with sleep hygiene.
Scholars at the University of Chicago conducted A 3-week study in overweight young adults who slept less than 6.5 hours. Each subject was given individual recommendations to improve sleep hygiene. After following the recommendations, the experiment participants began to sleep an average of 1.6 hours more, which reduced their overall appetite by 14%, and cravings for sweet and salty foods by 62%.
Similar results were received and in a study by researchers at King’s College London, an increase in short sleep reduced the amount of fat and carbohydrates consumed.
Thus, the restoration of normal sleep duration helps to reduce the calorie content of the diet, and therefore reduces the risk of obesity and other endocrine disorders associated with it.
Researchers at the Free University of Brussels conducted study among men with sleep deprivation. After improving sleep hygiene and increasing its duration by 1 hour, the participants in the experiment increased tissue sensitivity to insulin and decreased the likelihood of type 2 diabetes.