Night Shift Workers Can Mitigate the Risk of Metabolic Disease by Not Eating at Night

Medcram.com Dr. Roger Schweilt here with medcram.com and today we're going to talk about night shift workers and the issues involved with their cardiac and metabolic issues like diabetes and increased cardiovascular issues and clotting that night shift workers typically have. Now, this is near and dear to my heart because I'm a critical care physician. I'm also a sleep physician, and so I should know better. But the fact of the matter is we have to do critical care work at night as well. And so this affects me. It affects me, affects the nurses that I work with. It may affect you out there if you've done night shift work and it may affect some of your loved ones. So getting this information to them is really important because if the studies that we're going to review today are correct, there actually can be something that we can do about this. Please join us@medcram.com it does cost money for us to get these things edited. We try to make these things free as possible. And so your support is helpful. Join us@medcram.com for continuing medical education videos or videos on health topics. Okay, let's get started. This is a good introductory review article that was just published this year looking at not only the central clock in our brain called the suprachiasmatic nucleus, which sort of controls our circadian rhythm, but also these other things that we don't talk much about. These peripheral clocks. There are coordinating clocks in all the different organs of the body. And today we're going to look at the digestive organs of the body, so the liver, the stomach, the GI tract, et cetera. And these peripheral clocks are set by things that can influence it. And those things that we talk about are called zeitgebers. It's a German word that is meant for something that sets the time. And we've talked a lot about the suprachiasmatic nucleus in the brain and how it is affected by light in the eyes. And in that situation, for the central clock called the suprachiasmatic nucleus in the brain, that light is the zeitgeber for that master clock, which affects just about all of the other clocks in the human body. However, it's not the only effector. There are clocks in the GI tract that are set by when, for instance, you take food in, when you take calories in. And this is a really interesting article talking about those peripheral clocks and then specifically how they align with the central clocks.

Let's take a look at this article. The first part of this Talks about.

The suprachiasmatic nucleus, how it's the master clock. But then it says that there are peripheral clocks in the organs, like the brain, beyond the suprachiasmatic nucleus, but also.

The heart, the liver, the gut, gut.

The pancreas, adipose tissue, the adrenal glands, the lungs, skeletal muscles. And their clocks operate basically on the same machinery as a suprachiasmatic nucleus. So what are the zeitgebers that influence the peripheral clocks? And it gives a list there. So light is one of them. But specifically feeding temperature, hormones, glucocorticoids, insulin.

Even bacterial metabolites in the GI tract can influence these peripheral clocks.

Exercise, social factors and things of that nature. What we need to do to understand exactly what's going on, especially when we're talking about the diet, obesity and these.

Things that we see with people who do night shift, is what's going on.

With the peripheral clocks at night. And this article goes on to talk about the clocks that are in the gut and how different things can actually affect it, including short chain fatty acids and when you eat. And it says here, very interestingly, that time restricted feeding can restore the rhythm of the clock in the GI tract. That's going to be important because we're.

Going to be talking about some interventional studies here in just a bit. The liver has its own clocks that's.

Actually running as well as well as adipose tissue. And so this can be very important.

There can be even in the peripheral.

Clocks, circadian misalignment from shift work, jet lag, genetics or lifestyle. These can cause systemic dyssynchrony, contributing to metabolic syndrome, cardiovascular disease, neurodegenerations, cancer, immune disorders and inflammation. These are the things that we see in night shift workers.

We won't get into the studies, but.

There'S been multiple studies that have actually shown that this is the case. And we've actually talked about it before when we talked about the effect of light on our circadian rhythm and making sure that it is entrained. What can we do to mitigate these issues and metabolic factors in people who work the night shift? These poor people that have to work the night shift do this to save patients lives.

And if they're putting their own lives.

And their own longevity at stake, what can we learn about this so that we can actually help them? Interestingly, there have been two papers published.

That we're going to look at in.

Regards to metabolic effects. One that was published back in 2021 and another one that was just published this year. In 2025. Actually, they're based on the same intervention, but there was some secondary endpoints. So the first paper titled Daytime Eating Prevents Internal Circ, Circadian Misalignment and Glucose Intolerance in Night Work. And the second paper, which goes into more detail, which we'll talk about the results of as well, titled Daytime Eating during Simulated Night Work Mitigates Changes in Cardiovascular Risk Factors. Secondary Analyses of a Randomized controlled Trial. It's published in Nature. The first one was published in Science. So let's talk about exactly what they did here. So they recruited a bunch of people, 217, as you can see here.

They tried to see who was eligible.

For it, making sure that they could maintain the schedule that they could make sure was timed in terms of circadian rhythm at their baseline. So if they were unable to maintain a regular pre laboratory sleep wake times, then they were ineligible. And they basically got it down to about 20 subjects. And they divided these randomly into 10 on one side and 10 on the other, basically got them into doing a night shift work after some period of time. We'll talk about the details of that. They gave them food to eat, but in one group, the nighttime meal control group, they were able to eat anytime they wanted to in the day. At night, it didn't matter. They could eat anytime. It was spread out throughout the day and the night. In the intervention group, they had the daytime meal intervention group only. So in other words, these people in the intervention group had the inability to consume meals during simulated night work. In other words, they would go in for a work shift and they would not eat. They're eating was time restricted to the daytime, even though they were working at nighttime. So you're probably thinking first off, so they're supposed to eat and sleep at the same time. And the answer is yes, they would actually interrupt their sleep with meals. This is an interesting concept to see what would happen. The reason why they're looking at this is there's two factors here. And again, it has to do with the peripheral clocks and the central clock. So when people typically work night shift, they haven't completely shifted over from the central aspect of this. And so if they start to eat at night, this is actually outside of when the peripheral clocks are set. And so the question is, do we have a disagreement between the central oscillators, the central clocks and the peripheral oscillators? And that's what's trying to be shown here with these people in this group up here who are eating at night and working at night. And you can see here that the central clocks haven't fully adjusted, but their peripheral clocks are totally out of sync. And so there's a disagreement between these two. Whereas people, people who are night shift workers who do not eat at night, but eat during the day when they're sleeping, they would have a more agreeable circadian oscillator agreement. That's really what it is that they're looking at. We're going to actually show this in terms of what they actually did.

But let's take a look here first. I'm going to read here out of the study.

They say here, controlled human experimental studies show that misalignment between the central circadian clock and daily behaviors typical in night workers impairs glucose tolerance. Furthermore, eating during the nighttime impairs glucose tolerance, whereas not eating at night does not impair glucose tolerance.

So these are studies that have already been done on this.

These findings indicate adverse glycemic effects of mistimed food intake. Animal work indicates that restricted food intake to the active phase in rodents can prevent adverse metabolic effects of simulated shift work. Together, these findings raise the question of whether appropriate meal timing can prevent the adverse effects of circadian misalignment during night work in humans. Animal work suggests that the adverse metabolic consequences of circadian misalignment are due to a state of internal circadian misalignment between the two clocks synchronized by the central circadian pacemaker versus those synchronized by the fasting eating cycle. So again, we've got the gut oscillators that get most of their zeitgeber input from whether you're eating or not. And then you've got the central circadian rhythm and the suprachiasmatic nucleus, which is dependent on light and activity, et cetera.

So then what happens, as it says here, is that there is subsequent disruption of anabolic and catabolic processes resulting in suboptimal metabolism, which is exactly what we see in these night shift workers. Let's carefully look at the experimental design.

Basically, what we see here is the.

People on the left which basically were allowed to eat anything they wanted to. This is the nighttime meal control group. So they were able to eat at night. And over here we have the daytime meal intervention group. These are the people that were not.

Allowed to eat at night.

They start off basically as day shift workers. And this is an important limitation of this study, is these are not people that are already working at night. They took volunteers and they turned them into night shift workers. And they wanted to make sure that they kept the circadian rhythm at the night shift so they could actually test them. So what they did is on the first day, as you can see here, both groups basically were awake, that's bright light here in yellow. And then they made them turn off the lights at around 9 or 10pm and then they had these little areas in between where they turned on the light at 3 lux. But basically nighttime was exactly when nighttime would be the next day, daylight. Again, you can see they did this on both sides. And they did this for a couple days to make sure that their circadian rhythm was the same and it was daytime. Then they did this free running time here. This is a constant routine or CR, where basically they gave them low light 3 lux, and they had it on the whole time. In other words, they tried to get them into a different circadian rhythm and tried to shift them slowly to going in at night. They started the nighttime at 3pm and as you can see here, they did this on both sides. They eventually got them to the point where daylight and then lights off at about 2 o' clock in the afternoon, about 1 to 3 there, and then these nighttime periods. And then finally they got them to the point where there was this low level light by day seven, a couple of night periods here. And then finally they got them switched over to where they were basically doing night shift work and sleeping. So notice the lights are off here during the daytime. And then finally they washed it out again with another constant routine. And then they put them back to basically daytime in the morning and nighttime at night as it would normally be. So they did exactly the same type of lights on, lights off. However, the difference is that there was the feeding periods of time which are here in red. And notice in our nighttime meal control group that they were eating both during the day and at night. It was, in other words, all throughout the entire 24 period. However, notice here, in our daytime meal intervention group, it was only during the day and they had it dispersed throughout and noticed that they were sleeping in between these periods of time. In other words, what we're doing here is we are restricting eating to the.

Period of the day where the peripheral.

Clocks would be expecting it. Whereas here we're spreading out the mealtime to periods when the peripheral clocks in the GI tract are not going to be expecting it. So no feeding here. However, there is feeding here. That's the difference. And we want to know whether or not this is going to make a difference. So let's take a look at the results. The first result we have the nighttime meal control group here on the left and in orange, and the daytime meal intervention group here on the right in blue. And the first thing that we're looking at is core body temperature. Now, core body temperature is one of those things that is the result of the central circadian rhythm, not the peripheral one that's associated with the gut. And so, as you can see here, there's not really a big difference between these two. And this is exactly what we would have expected. The relative clock times you can see here, that obviously got shifted and there really is no difference. Let's take a look now at glucose. And when we look at glucose, we will see here first of all, that the measurements here in black on both of these sides, both the nighttime meal control group and the daytime meal intervention group, are the initial baseline values that they got at the very beginning before they underwent the oscillation of the circadian rhythm. And then the orange here and the blue is after they went through that and had the meals either throughout the entire night and day here on the left, or just meals during the day and not during at night here on the right. Now notice because the peripheral clocks were being stimulated out of phase of when they should use be. Notice that there was a complete difference in terms of what it was previously and what it is now. What it was previously is this black line. That's what the baseline is. And now notice that when people are allowed to eat when they're working night shift, both in the day and at night, notice that there is almost a complete out of phase. Notice, however, that in these people over.

Here who are just allowed to eat.

During the day when they were sleeping and not at night when they were working, there was a very minimal difference between what was initially at baseline and then what is now here after they've gone through the study. Very interesting results there on the glucose concentrations. When we look at insulin, we wonder, is the reason for that glucose change? Insulin? The answer is not really. There wasn't that much of a change. And if there was a change, it was very similar. So we don't see the glucose changes between these two randomized groups as being a result of an insulin difference. It may be from glucose neogenesis in the liver, which is part of that gut system that has a peripheral clock. Let's take a look here again at glucose and insulin, but particularly let's look at breakfast, which was the first meal of the day. And for those that were eating all throughout the day, that was breakfast. For those who were just eating in the daytime, again, that would be breakfast. When they get home. Notice the difference here in terms of glucose. There is a huge difference in terms of the glucose from breakfast in these people that were able to eat any time of day versus those that were only eating in the daytime. Specifically, notice that the blood sugars were actually lower than the baseline. Even though these people were working at night, they actually had lower glucose concentrations when they only ate during the day, not when they were able to eat at any time. And by the way, in the materials and the methods of this study, these are very strictly measured and given out meals that had the same amount of proteins, fats and carbohydrates. And you can see here clearly that there was a big difference in the glucose concentration. If we look at insulin concentrations, we can see that there might be a little bit of a change in how the insulin was secreted, but overall there was really no difference in the total amount of insulin both before and after and in both those that had no restrictions on when they ate and our intervention group here when they had a restriction of just eating during the day. Day, let's look at nighttime nighttime control not for breakfast, but for dinner. Notice not a huge difference between any of these in terms of glucose and insulin. Let's go back once more. Breakfast is where we saw a big difference. Dinner not that much of a difference. So here's a summary that I put together of what the authors got from this study. This study shows that simulated night shift work causes internal circadian misalignment and impairs glucose tolerance, largely due to mistimed food intake. When participants ate meals at night, that's in the group on the left, their circadian glucose rhythms shifted out of sync with central circadian rhythms, resulting in impaired glucose tolerance and reduced pancreatic B cell function. In contrast, when meals were restricted to the daytime in the group on the right, circadian alignment was preserved despite night work and glucose tolerance remained normal. These findings suggest that food timing strongly influences peripheral circadian rhythms and metabolic regulation independent of the sleep wake cycle. Eating at night disrupts circadian coordination and glucose metabolism, while daytime eating aligns feeding with the central circadian pacemaker, maintaining pancreatic function and preserving dysglycemia. The study highlights that meal timing as a practical behavioral intervention to mitigate the metabolic risk of shift work, particularly the elevated risk of glucose intolerance, insulin resistance, and type 2 diabetes. Since most nightworkers do not fully adapt their circadian system to the night schedules, aligning food intake to the habitual daytime may be an effective strategy to protect metabolic health okay, so we just looked at this first study here. Now what we're going to do is look at the follow up study that was just published this year in 2025, looking at these secondary analyses in these endpoints.

So here's a category looking at something called the PNN50. The group here on the left able to eat any time of day or night, and those on the right were restricted to only eating during the day. And you can see a huge difference here. Black again is the baseline, as you can see here. And if you notice in the group that was restricted to the day, there's not a huge difference between those numbers that they got at the beginning and those numbers that they got at the end. However, there's a huge drop in the PNN50. So what does that mean? What is the PNN50? It indicates that being low reduced vagal tone, that means the vagus nerve, which is a parasympathetic nerve and a relative shift towards sympathetic dominance. What we're seeing here is because the PNN50, which is a measure of heart rate variability and things when that goes down, that means that we're seeing more of a sympathetic nervous system drive. That's not good.

So where do we see this?

We can see this in stress, anxiety, poor sleep, acute illness, sepsis, systemic inflammation, cardiovascular disease like heart failure, post mi, diabetes and other metabolic disorders, and also aging. So clinically, a low PNN 50 and a low heart rate variability in general is associated with worse cardiovascular and overall health outcomes, including a higher risk of arrhythmias and mortality, especially in cardiac patients. What are we seeing here after just a week or two, making sure that these subjects are working at night and they're able to eat at any time, we're seeing a pretty dramatic shift in something that we know is predictive of these bad outcomes here in that cohort. Those subjects that we're told don't eat at night, only eat during the day, we don't see any of it. We're able to completely mitigate the surrogate for bad outcomes. Let's look for another outcome. This is called the rmssdms. And again we see that it's dropped as well. In our group that was given food all throughout the day and night. What is the rmssd? It's the square root of the mean of the squared differences between the NN intervals. This is looking at the heart primarily reflects parasympathetic activity. So it is going down. And of course, if parasympathetic activity is going down, it indicates that there's more sympathetic activity. So again, if it's low, which it is here, in the group that was allowed to eat all throughout the day and night, it indicated reduced vagal tone seen in stress, illness, aging and cardiovascular metabolic disease. It's widely used in both clinical cardiology and sports physiology as a marker of recovery and autonomic balance. And see here, it's out of balance just within a week or two of doing this. Let's look at another one here, the LF to HF ratio. What is the LF to HF ratio? This looks at sympathetic dominance. And again, it's up in stress, anxiety, illness and in heart failure. It's common in acute stress states or cardiovascular disease.

And what do we see here?

It's actually up, just as we would predict, but we do not see it up in the group that refrained from eating food at night, only ate it during the day. This is the plasminogen activator inhibitor 1, otherwise known as PAI1. Once again, we see an increase in these patients, but we don't see it in the patients that were restricted to eating during the day. In the context here of blood clotting, an Elevation in PAI1 plays a critical role in maintaining hemostatic balance. Elevated PAI1 levels can impair fibrinolysis. That means the breakdown of blood clots, and this leads to increased thrombosis risk. This is an issue and may explain why we see increased blood clots in those people who work at night, for instance. It has been identified as a major determinant in inhibiting arterial clot lysis and is linked to pathological processes such as inflammation and cardiovascular events. We have seen multiple endpoints here that show that, at least in this cohort, there is a way to mitigate, reduce, almost completely eliminate, in some of these cases, the added risk of working at night. There are some limitations to the study. These were people that were 18 to 30 years of age, so this may not work as well for middle aged and older adults. This is a small sample size. There was 10 in one group and about 10 in the other group. There was some strict inclusion criteria. It would be nice to see this a little bit more opened up. Here's the other limitation. These participants were not actual shift workers that have been doing it for years. These were people that were brought onto the shift and had their circadian rhythm shifted over and then used those subjects in the trial to do a randomized intervention which restricted feeding to just during the day. Another limitation was that circadian misalignment was induced by a forced desynchrony protocol which may not fully reflect real life night shift conditions. So really this needs to be done again on a larger platform. Laboratory conditions provided high experimental control but limit direct translation to real world settings. Unclear in a real world setting if this would have the same type of benefit or maybe the same benefit, but to maybe a less of a degree. Because of all these limitations, we really need to do this type of study and larger clinical trials involving real shift workers. Permanent, rotating, irregular morning and evening shifts to confirm whether or not this type of intervention will have the same benefits in these broader populations. Until that time comes, we can say that apparently one of the things that night shift workers may want to do if they want to get a benefit of this and see if it works for them, is to work at night as they are, but when they get home, it's to have a meal, to sleep for about three hours, wake up, have a meal, sleep for three hours, wake up, have a meal, and then that last meal may be optional if they want to do that before they go to work and then when they're at work. The key here is not eating anything. And that might be difficult because I know the culture at night. I know that people bring things in for the nurses at night, like pizza, donuts, they have parties, it's not easy to not eat. And of course this goes beyond the medical culture because there are night shift workers all over the world doing things more than just medicine. I don't know exactly what their cultures are, but I can assume it's probably very similar because human beings are pretty similar. Wherever you go. It may be based on this evidence, if this is applicable to a larger population, that refraining from eating on your night shift may actually prevent you from having many of these terrible diseases down the road, like heart disease, diabetes, obesity, strokes, cancer, things of that nature. So I hope you enjoyed this. If you are a night shift worker, you should review this and we'll put the links to those studies in the description below. If you know somebody who's a night shift worker, pass this information along to them. It could be very important. We may do this study years down the road and find that it works. And this was the first indication that this type of intervention might work. And so if there's something that you're interested in doing, you can adopt it. If you like this video, please Visit us@medcram.com Subscribe Turn on notifications Leave us a comment. Thanks for watching.