Sleep quality is inherently linked to glucose metabolism. Epidemiological studies have shown that people who have poor sleep are at greater risk of having or developing diabetes. When a person does not get enough sleep, their pancreatic beta cells become less sensitive to glucose signaling, reducing the amount of insulin produced by the pancreas. This, in turn, impairs glucose uptake, resulting in hyperglycemia, a hallmark of diabetes. In this clip, Dr. Matthew Walker explains how sleep deprivation impairs glucose metabolism, increasing the risk of diabetes and metabolic dysfunction.

Rhonda: So let's talk about your, because a lot of interesting research has come out of your lab on the blood glucose regulation front and, well, I guess more on the eating preferences...

Matt: And appetite and eating.

Rhonda: ...and appetite. Yeah.

Matt: I mean, the way I see it, it's all part of the energy intake expenditure system. And sleep, you know, if you think about like a weighing scale between sort of energy expenditure and energy consumption, sleep, if you're not getting it, just annihilates that balance. And we can speak about any one of those things.

But, you know, I think the blood glucose story and sleep is very very well-worked out now. It started with epidemiological studies, where we started to see that people who were sleeping less than seven hours were at significantly higher likelihood of either being diabetic or going on to develop diabetes. Many of them were already, you know, what we call a pre-diabetic state, or they had what we now call sort of metabolic disorder.

And then the question became, well, is that associational or is it causal? So the next studies that happened in this was work back in...starts in the 1990s by Eve Van Carter at the University of Chicago. Wonderful studies. It took a group of healthy people, started to limit them to different doses of sleep for a week, you know, five hours of sleep, six hours of sleep, four hours of sleep, and what she showed was that, essentially, after one week of short sleep, your blood sugar levels are disrupted so significantly that your doctor would classify you at that point as being pre-diabetic after one week of short sleep.

And the way that they do this is what's called a glucose tolerance test, where you are fasted, and then you are given this sickly-sweet drink of glucose, and then they are measuring from your blood in the next three or four hours how quickly is your body able to dispose of that blood glucose.

So what happens when you drink or when you eat a meal is that your blood sugar spikes. And you don't want that spike to stick around very long. If your body is healthy, it deals with that raised level of blood glucose very quickly, and it brings it back down very quickly. That's a healthy profile. That's what we call good glucose management. So how good is your body at disposing essentially of that glucose? And the way it disposes it is that cells in the body, including muscle cells, will suck up that glucose. And it's called your disposal index, or your disposition index, it turns out.

So what she found, Eve Van Carter, with her studies, was that, firstly, the way that your body knows how to absorb glucose and suck in that glucose is that there is another chemical called insulin, which is released by the pancreas, beta cells of the pancreas, and that insulin will instruct the cells of the body to open up special glucose channels to absorb the glucose and your blood sugar drops, which is good and healthy.

Firstly, what she found was that when you are not getting sufficient sleep, the beta cells in your pancreas stop being sensitive to the signal of high glucose. So the beta cells, which normally are listening for this spike in glucose, and as soon as they sort of, you know, hear...no, they're not hearing it. They're sensing it. But as soon as they sense the spike in glucose, they release insulin. And that insulin will drop your blood glucose.

But those cells had become insensitive to glucose, what we call sort of glucose insensitivity. And so the beta cells of the pancreas stopped releasing as much insulin. It didn't release enough insulin to drop blood glucose, so blood glucose remained high. If that wasn't bad enough, we've since gone on to demonstrate, and you can do this with really clever studies, taking tissue biopsies, the cells of the body including muscle cells and fat cells, their receptors stopped being as sensitive to insulin.

So, firstly, you're releasing less insulin when you're sleep-deprived. But what little insulin you do release is not instructing those cells to open up the channels to take away the monsoon of the glucose that's flowing in the channels of the body. So on both sides of the glucose regulation, on the release of insulin, to instruct cells to absorb glucose, and on those cells themselves to be sort of instructed by insulin, those cells became less sensitive to the insulin signal. And so, as a consequence, your overall ability to deal with glucose became far more degraded, and blood glucose remained higher, which sets you on a profile of looking pre-diabetic.

Rhonda: Couple that with the standard American diet, and, you know...

Matt: And you're off to the races in terms with...

Rhonda: Yeah, and eating late at night. So, actually, are you familiar with the studies, I know Dr. Satchin Panda actually is the one who told me about this, melatonin is actually what is responsible for shutting down the pancreatic beta islet cells from producing insulin. So I wonder how much of the sleep deprivation the melatonin system is involved in that.

Matt: Yeah. So in those studies, what was good is that they held constant circadian rhythms, they held constant ambient light, and they even held constant physical activity. The control group was sort of they were in bed for eight hours, but the people who are sleep deprived, limited to four or five hours, during the eight-hour window where the other people were actually sleeping, they had to lie recumbent in bed with no physical movement.

Rhonda: Oh, man.

Matt: So you controlled, but it was a great study because you control for physical activity as well. So we now really understand the link between a lack of sleep and poor glucose management, and very very well indeed. And we also know the stage of sleep that's important. It's, again, deep slow-wave sleep. The study that I described before, where you're playing those annoying tones just below the level of awakening so I can remove your deep quality of sleep, you can do that same thing again, and you essentially produce that same diabetic-like consequence just by removing or excising deep slow-wave sleep.