A new review published in the Lancet Diabetes and Endocrinology summarizes the emerging evidence that lack of sleep can have negative consequences for energy homeostasis and increased risk of the metabolic syndrome. There is an increasing number of studies now demonstrating that lack of sleep, including frequent sleep-wake patterns, and reduced sleep quality, can negatively impact on glucose metabolism and its related disorders. The authors suggest that these studies should lead to a greater awareness of the importance of regular sleeping patterns and sufficient sleep duration. In addition, the review suggests that the research may open up new avenues to treat the metabolic syndrome by outlining the physiological mechanisms involved.
The metabolic syndrome consists of several factors which include: visceral obesity, impaired glucose metabolism, dyslipidemia, and high blood pressure. The authors review the medical research that has assessed the link between reduced sleep and these factors that comprise the metabolic syndrome. It is important to note that in addition to a short duration of continuous sleep, ‘reduced sleep’ also includes frequent sleep-wake cycles, reduced sleep depth, irregular sleeping patterns, insomnia, and breathing disorders that disrupt sleep.
One study found an increase in metabolic syndrome from 22% to 48% when comparing participants who slept between 6-7 hours per night with participants who slept 7-8 hours per night. Additionally, in the group who slept very short periods of less than 6 hours per night the prevalence of the metabolic syndrome was increased to 83%. An interesting result uncovered by this study was that a longer sleep duration of 8 hours or more per night was also associated with an increased prevalence of the metabolic syndrome. The results of this study were supported by other studies that have also demonstrated an up to 57% increase in the risk of both obesity and type 2 diabetes in participants with reduced sleep patterns. There was also an increased rate of obesity in children who slept less than 10 hours per night.
The review also suggests that due to the metabolic syndrome increasing the risk of early death, sleep loss may also be associated with an increase in mortality. This was supported by a review of 16 studies that reported an increased risk of death associated with short sleep durations of less than 7 hours per night. There was also an increase in the risk of death associated with long sleep durations of more than 8 hours per night.
The authors summarized the results of available studies that have investigated the mechanisms that may underlie the increased risk of metabolic disorders caused by reduced sleep. Some of the mechanisms described include:
– Decreased insulin sensitivity
– An alteration in the transcription of genes associated with circadian rhythm, sleep homeostasis, and metabolism.
– Changes in neuroendocrine factors (eg ghrelin & leptin)
There is some evidence that reduced sleep adversely effects glucose metabolism via stimulation of the hypothalamic pituitary axis. Some studies also suggest that an increase in body weight in those who sleep less may be due to increased stimulation and food intake. In addition, ghrelin, which mediates food intake, has also been implicated in increased weight gain in some studies of sleep restriction, as well as reduced levels of leptin, which promotes an increase in calorie consumption following sleep loss. Another suggestion supported by several studies is that physical activity and energy expenditure is reduced following sleep loss. Consistent short sleep periods of less than 6 hours per night has been associated with a 27% reduction in total body movement, demonstrating an increase in sedentary tendencies of those who sleep less, thereby reducing the beneficial health effects of physical activity.
While some studies support these mechanisms, the results appear to be inconsistent across studies, and therefore requires further research. It seems most likely that a combination of mechanisms would contribute to the negative metabolic effects induced by insufficient sleep. Both physiological factors and behavioural factors are likely to play a role.
The authors suggest that knowledge of the risks and mechanisms involved in reduced sleep and the metabolic syndrome could give rise to new strategies to curb the rise in the metabolic syndrome and related metabolic disorders. Encouraging a healthy lifestyle through physical activity and nutrition, in addition to consistent and quality sleeping habits, could heavily impact on patients’ health outcomes.
There are several clinical trials currently recruiting that are assessing the effects of sleep duration on metabolic disorders, including type 2 diabetes, and obesity. A study being conducted at the University of Chicago, Illinois, United States is recruiting patients for testing the effects of deficient sleep on risk of diabetes. The effect of sleep on glucose homeostasis in pre-diabetes and type 2 diabetes is also being assessed at Beth Israel Deaconess Medical Center in Boston, Massachusetts, United States. In addition, at the University of California, San Francisco, United States, a study is also currently recruiting to test the effect of sleep on insulin sensitivity.
Studies assessing the effects of sleep duration in obese patients are currently recruiting at three centers in the United States: the University of Chicago, the Mayo Clinic in Rochester, Minnesota, and at the Weight Control and Diabetes Research Center in Rhode Island.
Schmid, SM, Hallschmid M, Schultes B. “The metabolic burden of sleep loss” The Lancet Diabetes & Endocrinology, Early Online Publication, 25 March 2014, doi:10.1016/S2213-8587(14)70012-9
Clinicaltrials.gov “Home Sleep and Circadian Phase: Mediators of Diabetes Risk” Available from: http://www.clinicaltrials.gov/ct2/show/NCT01786564?term=diabetes+sleep&recr=Open&no_unk=Y&rank=7Last Accessed: March 25, 2014.
Clinicaltrials.gov “Sleep Effectiveness and Insulin and Glucose Homeostasis” Available from: http://www.clinicaltrials.gov/ct2/show/NCT01887691?term=diabetes+sleep&recr=Open&no_unk=Y&rank=11Last Accessed: March 25, 2014.
Clinicaltrials.gov “Metabolic Study of Sleep Apnea in Men and Women” Available from: http://www.clinicaltrials.gov/ct2/show/NCT00706511?term=diabetes+sleep&recr=Open&no_unk=Y&rank=25Last Accessed: March 25, 2014.
Clinicaltrials.gov “Effects of Sleep Duration and Architecture on Insulin Sensitivity” Available from: http://www.clinicaltrials.gov/ct2/show/NCT01396941?term=diabetes+sleep&recr=Open&no_unk=Y&rank=31Last Accessed: March 25, 2014.
Clinicaltrials.gov “Short Term Effects of Increasing Sleep Duration”Available from: http://www.clinicaltrials.gov/ct2/show/NCT01428687?term=diabetes+sleep&recr=Open&no_unk=Y&rank=47Last Accessed: March 25, 2014.
Clinicaltrials.gov “Sleep Restriction and Obesity” Available from: http://www.clinicaltrials.gov/ct2/show/NCT01580761?term=obesity+risk+sleep&recr=Open&no_unk=Y&rank=1Last Accessed: March 25, 2014.
Image courtesy of graur codrin / FreeDigitalPhotos.net
Written by Deborah Tallarigo, PhD