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Relations between sleep, sleep restriction and metabolism

For various reasons related to work, study, leisure and family, individuals sleep less and less. Not only that, the rate of sleep disorders in megalopolises like São Paulo is very high. Results from EPISONO, an epidemiological study that tracks complaints and sleep disorders in the city of São Paulo, indicate that around 45% of the population has some complaint of insomnia or difficulty sleepingCASTRO; POYARES; LEGER; BITTENCOURT et al., 2013and 33% of the population has obstructive sleep apneaTUFIK; SANTOS-SILVA; TADDEI; BITTENCOURT, 2010Furthermore, even if we consider healthy individuals without sleep disorders, natural aging leads to a reduction in total sleep time and sleep quality, characterized by greater fragmentation of the sleep periodVAN CAUTER; LEPROULT; PLAT, 2000Therefore, considering the magnitude of people affected by poor sleep quality and insufficient duration, the objective of this article is to elucidate the relations between sleep, sleep deprivation/restriction and metabolism.

Hormonal regulation

During sleep, several important reactions occur in our body. Specifically, during slow-wave sleep, there is a reduction in blood pressure, heart rate, reduced central nervous system sympathetic activity, and increased parasympathetic activitySOMERS; DYKEN; MARK; ABBOUD, 1993as well as reduced glucose metabolismZOCCOLI; WALKER; LENZI; FRANZINI, 2002In addition, the release of hormones from the hypothalamic-pituitary-adrenal axis, such as cortisol, is inhibited, while the release of growth hormone (GH) and prolactin is increasedFRIESS; WIEDEMANN; STEIGER; HOLSBOER, 1995Both hormones, GH and cortisol, have a significant impact on glucose regulation. Aging reduces the proportion of slow-wave sleep, and this reduction is associated with reduced GH secretion between youth and middle age, as well as between middle age and senescence, and this reduction in GH secretion was associated with reduced slow-wave sleep regardless of age. In 2011, Le Proult and Van Cauter demonstrated the effect of one week of sleep restriction on serum testosterone levels in 10 healthy adult menLEPROULT; VAN CAUTER, 2011The results showed that testosterone levels were reduced by 10 to 15% from baseline levels after the 5-hour sleep restriction period per night. Furthermore, this reduction was correlated with lower vigor levels. By way of comparison, natural aging leads to a reduction in testosterone levels by a proportion of 1 to 2% per year. Considering that androgen deficiency symptoms include low energy levels, reduced libido, concentration problems and increased sleepiness, this becomes a major problem in the population.

Considering these facts, it is to be expected that the impact on glucose regulation will generate negative consequences in the body. During periods of sleep restriction, there is a significant reduction in glucose tolerance compared to periods of complete restSPIEGEL; LEPROULT; VAN CAUTER, 1999Evidence indicates that reduced slow-wave sleep in healthy individuals leads to reduced insulin sensitivity, reduced glucose tolerance and increased risk for developing type II diabetesTASALI; LEPROULT; EHRMANN; VAN CAUTER, 2008These data are supported by epidemiological studies, indicating that individuals who sleep less are more exposed to the development of diabetes. A 10-year prospective study evaluated 70,026 women and demonstrated that volunteers who slept 5 hours or less per night were at greater risk for developing diabetes than volunteers who slept 8 hours per nightAYAS; WHITE; AL-DELAIMY; MANSON et al., 2003).

Sleep duration and appetite regulation

Food intake is regulated by the neuroendocrine system. The hormone leptin exerts an inhibitory effect on food intake (satiety) and increases caloric expenditureSCHWARTZ; MORTON, 2002). On the other hand, ghrelin is a hormone secreted by the stomach that stimulates appetite. Under healthy conditions, ghrelin levels rise just before meals and drop right after eating food. Studies show that chronic sleep restriction is associated with reduced levels of leptin and increased levels of ghrelinSPIEGEL; TASALI; PENEV; VAN CAUTER, 2004Furthermore, an increase in the ghrelin/leptin ratio is correlated with a greater appetite, especially for foods rich in carbohydratesSPIEGEL; TASALI; PENEV; VAN CAUTER, 2004). Finally, the reduction in leptin levels observed after sleep restriction is similar to the reduction observed after energy restriction of 70% (reduction in leptin levels of 26% and 22%, respectively).

Finally, researchers in the field agree that the increase in obesity rates of population is not explained only through eating habits and physical exercise. Population studies involving nearly 1,000 adultsCHAPUT; DESPRÉS; BOUCHARD; TREMBLAY, 2007and 10,000 childrenSEKINE; YAMAGAMI; HANDA; SAITO et al., 2002) indicate that total sleep time is an important risk factor for of obesity. Evidence indicates that the levels of adiposity and obesity are reduced in individuals who sleep 7-8 hours a night, compared to those who sleep 5-6 hoursCHAPUT; DESPRÉS; BOUCHARD; TREMBLAY, 2007).

Conclusion

Scientific evidence indicates that sleep is essential for the regulation of various metabolic processes, so sleep restriction increases the likelihood of developing metabolic diseases such as diabetes and obesity. These deleterious effects occur through several factors, including the imbalance between the key hormones for appetite regulation: leptin and ghrelin, in addition to changes in glucose metabolism. Considering these observed losses, it is critical that individuals are made aware of the importance of sleep, as well as receive support in order to develop strategies to positively modify the quality and duration of sleep.

Sleep pattern assessment

Actigraphy is a non-invasive technique that can be used to assess sleep pattern and sleep-wake rhythm. The actigraph is a wristwatch-like device that contains light, motion, and temperature sensors. Through this information, it is possible to extract data regarding variables such as total sleep time, latency to sleep onset, time awake after sleep onset, sleep efficiency, time awake and variables related to rhythm, such as cosinor, spectrogram, periodogram, and non-parametric variables such as L5, M10, IS and IV.

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