The duration and quality of sleep has been strongly linked to many metabolic problems, such as low HDL cholesterol, higher body mass index (BMI), high blood pressure, high triglycerides and type ΙΙ diabetes.

As it was published in the journal Diabetes Care, a study found an increased risk of metabolic problems of up to 27%, for every hour one changes the quality or quantity of sleep. This study involved 2,003 people between the ages of 45-84 who were monitored for an average of 6 years.


Endocrine mechanisms of disturbed sleep

Various biological mechanisms have been found to be associated with short sleep duration and metabolic disorders, such as autonomous nervous system involvement, endothelial function, metabolic rate, inflammation.

Over the last decade, several studies have suggested that sleep disorders adversely affect not only cognitive functions and performance, but also cardiovascular function and even mortality. More recently, it has been recognized that sleep is causally linked to the regulation of glucose homeostasis and appetite control, and that disturbed sleep contributes to the prevalence of obesity and type ΙΙ diabetes mellitus (T2DM) worldwide.

Despite the clear correlation between sleep deprivation and metabolic disorders, the underlying endocrine and molecular mechanisms remain only partially elucidated. Some studies have reported disturbances in cortisol and catecholamine levels. The complexity of the associated endocrine mechanisms can be further demonstrated by observations of elevated levels of proinflammatory cytokines, low free testosterone, decreased thyroid hormone levels, decreased growth hormone secretion, and changes in adipidocrine-induced lipids.


Regulation of appetite

Prospective studies have also identified short sleep duration as an independent risk factor for weight gain and belly fat accumulation. Experimental evidence supports this relationship, as people with sleep disorders express a preference for foods high in fat and carbohydrates and increase their daily calorie intake by ≈ 20%. Therefore, it is reasonable to assume that insufficient sleep stimulates food intake and contributes to the development of obesity and metabolic syndrome. Furthermore, short sleep duration has been associated with decreased leptin (reduced food intake, produced by adipose tissue) and increased ghrelin (increased food intake, excreted mainly by the stomach).


What happens while we sleep?

During normal sleep, the energy consumption of the whole body is reduced by 15-35%. Furthermore, the glucose, lipid and protein cycle fluctuates significantly during the natural sleep / wake cycle, which is independent of the changes that are caused by food intake. For example, plasma glucose levels strongly follow the circadian rhythm and gradually increase during sleep with the highest levels early in the morning. Upon awakening, hepatic glucose production increases and contributes to the “dawn effect” in both healthy and diabetic individuals. In addition, reduced activity of neurons during sleep helps to reduce glucose uptake by the brain. Similar circadian sleep / wake changes have been described in lipid metabolism. Plasma triglycerides and fatty acids present strong circadian changes with gradually decreasing levels during sleep, when lipoprotein lipase (LPL) activity and fatty acid synthesis in adipose tissue are at their highest.

So the duration of sleep is negatively related to BMI and therefore to obesity and waist circumference and is positively associated with HDL cholesterol levels. Short sleep duration means reduced glucose metabolism and thyroid function, as well as higher systemic inflammation. Also, sleep duration tends to be negatively correlated with HbA1c, which is positively associated with free T4 and negatively associated with CRP (a biomarker associated with inflammation). Furthermore, it is negatively correlated with triglycerides and metabolic syndrome criteria.


Take home Message

If one or more of the above mentioned data alarmed you, start by examining your sleep pattern. Do you sleep well and enough?

If you do not feel sure about your sleep hygiene, consult a Health Professional. Your Doctor can assess your sleep patterns and guide you along pathways that will improve your sleep and overall Health levels.

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