Deep-sleep brain waves are linked to blood sugar control

Several studies have linked sleep problems to poor blood glucose control. Insufficient sleep duration, poor sleep quality, and sleep disorders such as insomnia and sleep apnea are all associated with raised blood glucose levels and an increased risk of type 2 diabetes.

Now, a study has suggested that the quality of sleep is a better predictor of blood glucose levels than the quantity of sleep, and has proposed a mechanism by which deep sleep is related to lower blood glucose levels.

The researchers found that some deep-sleep brain waves are linked to better blood glucose control the following day.

The study, which is published in Cell Reports Medicine, suggests that by activating the parasympathetic nervous system, deep sleep increases the body’s sensitivity to insulin, improving blood sugar control.

Vyoma D. Shah, a researcher at the Center for Human Sleep Science and co-author of the study, told Medical News Today that “[t]he association with blood glucose control appears to be strongly explained by a link between deep sleep oscillations and specific alteration in insulin sensitivity, rather than insulin synthesis, storage or secretion.”

”The causal chain by which this happens in humans is still unexplored,” the researcher pointed out.

Fiona McLoone, research communications officer at Diabetes UK, not involved in this research, commented for MNT:

“This study tells us more about how the brain is involved in controlling blood glucose levels while we sleep; however, more research is needed to find out if support to improve sleep could help people with or at risk of type 2 diabetes.”

Previous research has suggested that a reduction in slow-wave, or deep, sleep duration is associated with impaired glucose metabolism.

A laboratory study found that when slow-wave sleep was suppressed in healthy young adults, their insulin sensitivity decreased markedly, leading to reduced glucose tolerance and increased diabetes risk.

Findings in a study in rats showed that within 10 minutes of clusters of sharp wave ripples from the hippocampus — which occur in non-REM sleep — the rats showed a decrease in blood glucose concentrations.

In the current study, the researchers first analyzed overnight polysomnography data and next-morning glucose and insulin measurements for 647 people. They then repeated their experiments in another group of 1,996 people.

They were testing whether coupled non-REM sleep oscillation spindles the night before are associated with improved peripheral blood glucose levels the following day.

In both groups, they controlled for other factors known to affect blood glucose control, including age, gender, race, body mass index (BMI), hypertension, quantity and quality of sleep.

They found that the coupling of deep-sleep brain waves, specifically sleep spindles and slow waves, was associated with improved control of blood glucose the following morning.

“Slow-oscillation spindle coupling has traditionally been associated with learning/cognitive related functions. Here, we demonstrate their association with a physiological body function, that of glucose homeostasis, in humans, for the first time.”

– Vyoma Shah

The authors suggest that the effect on blood glucose might be due to the activation of the parasympathetic nervous system.

They found that when deep sleep switched on this part of the nervous system, the body’s sensitivity to insulin increased, prompting the absorption of glucose from the bloodstream into cells, therefore lowering blood glucose.

Shah commented:

“Whilst there are multiple techniques that can alter brain waves during sleep — electrical, audio stimulation, better sleep hygiene to improve the ease of falling asleep and the chances of staying asleep — the findings from our study are not relevant to all deep sleep in general, but specific to the coupling (nearly simultaneous or time-locked occurrence) of slow oscillations and spindles in deep sleep.”

If this effect could be induced in people at greater risk of prediabetes or diabetes, it could help prevent harmful blood sugar spikes.

The researchers caution that their findings cannot show a causative relationship between deep sleep and better control of blood glucose. However, they do suggest a mechanism for the association.

Shah explained that “[b]ased on a seminal study in rats (which inspired this study), it is plausible that hippocampal sharp wave ripples during sleep — which we index by measuring slow oscillation-spindle coupling in this study — send a signal to a relay station called the lateral septum, which in turn modulates blood glucose levels.”

The authors also suggest that mapping deep-sleep brain waves may be a non-invasive method for predicting a person’s blood sugar control.

“Our findings are the first to show an association between these specific deep sleep brain waves (slow oscillation-spindle coupling) and glucose regulation, re-emphasizing the importance of sleep in the clinical management of hyperglycemia,” Shah told us.

“We hope this study paves the way for future research that is able to better understand the causal mechanisms underlying these associations, and eventually, develop therapeutics to enhance slow-oscillation spindle coupling during sleep, to better control blood sugar levels,” she added.

She also highlighted directions for future research, including assessing glucose measurements at multiple time points, and testing bidirectional causality by manipulating slow oscillation and spindle coupling to alter glucose regulation or vice versa.

But sleep is not a magic bullet for reducing diabetes risk, as McLoone advised: “Some people are more at risk of developing type 2 diabetes than others, and getting a good night’s sleep is an essential component of good health, but currently the best evidence for reducing [the] risk of developing type 2 diabetes involves eating a healthy, balanced diet and keeping active.”