[318] - What Are IPRGCs and Why They Matter for Shift Workers

Light is the most powerful signal for your body clock—but most shift workers never train it on purpose. In this episode, I explain how your eye’s light-sensing cells set circadian timing and show you exactly how to use morning light, controlled darkness, and smart lighting habits to stabilise sleep, mood, digestion, and energy across any roster.

What You’ll Learn:

• What IPRGCs are and how they differ from rods and cones
• How light signals reach the SCN and set circadian timing
• Why morning light anchors alertness and rhythms
• How evening blue light suppresses melatonin
• How shift work disrupts the body’s clocks
• Practical light strategies for day, afternoon, and night shifts
• When to use blue-blocking glasses after nights
• Home lighting swaps and screen hygiene that protect sleep
• How light timing affects appetite, metabolism, and gut rhythms
• Simple consistency habits to stabilise your clock long term

If you want help building the right light routine for your roster, reach out through the link in the show notes.

Subscribe so you never miss an episode, and please leave a rating and review—it helps more shift workers find the podcast.

Chapters

• 4:51 Welcome And Mission To Thrive
• 6:03 Meet The IPRGCs And Why They Matter
• 8:31 How Light Sets The Master Clock
• 11:25 Morning Light: Sky Before Screen
• 13:35 Night Light Pitfalls And Melatonin
• 15:45 Shift Work Conflicts With Biology
• 18:16 Practical Light Rules For Each Shift

Transcript

SPEAKER_00: 3:17

Shift work can be brutal, but it doesn't have to be. Welcome to a healthy shift. My name is Roger Sutherland, certified nutritionist, veteran law enforcement officer, and 24-7 shift worker for almost four decades. Through this podcast, I aim to educate shift workers using evidence-based methods to not only survive the rigors of shift work, but thrive. My goal is to empower shift workers to improve their health and well-being so they have more energy to do the things they love. Enjoy today's show. And welcome back to a healthy shift podcast. My name is Roger Sutherland, and I am your guide on this shift working journey that you have undertaking. And I'm here to help you to thrive, not just survive in your shift working life. If there's one thing that I really want to do, and that is to give shift workers more energy to do the things that they love outside of their shift working life. Because when we are absolutely thriving outside of our shift working life, we turn up as a much better person at work. And that is something that's really important. Now, today I talk about circumstances rhythms and I talk about light, but I want to talk about something that I've never spoken about yet. And I think it's something that's really important. Today, I want to explain something that most people have never heard of. But it literally drives a huge part of your health as a shift worker. And they are called intrinsically photosensitive retinal ganglion cells. And what I'm going to do is I'm actually going to call them IPRGCs from here on in. But that's what they are. I'll say that again. Intrinsically photosensitive retinal ganglion cells. Don't panic, I will explain everything. These cells actually decide how your body reads light. That's right. And if you don't understand them, your sleep, your mood, your energy, and even your digestion can seriously drift out of rhythm and cause all sorts of complications for you. So let's break it down into very, very simple terms. Let's start off with what are IPRGCs? Well, most people know that the eyes have rod and cones, right? The rods they help you to see in low light, and the cones actually help you to see color and detail. That's what the rods and cones are. Now, IPRGCs are not like rods and cones, they are actually a completely separate group of cells that sit in the eye that do not help you to see pictures at all. They don't even make an image. What they are is a light sensor. Now these cells contain a pigment which is called melanopsin. And melanopsin reacts to light. And guess what? Blue light, especially to bright morning blue light. What I want you to do is I want you to think of your IPRGCs as your body's light meter. Now they're based in the eye, they are not in the rods and cones, they are not in the cornea, uh the cornea. Yep, they are literally on the eyeball, but at the back of the eyeball next to where the optic nerve goes through. What they do is they actually tell your brain what time of the day it is based on the particular light hitting your eyes, that blue light. So how do they differ from the resonar? Well, the resonant actually helps you to see. What it does is it sends detailed images to the visual part of your brain. Now the IPRGCs don't do that. What they do is they send information directly to a small part of the brain, which is called the suprachiosmatic nucleus or the SCN, which I will call it from here on in. Now the SCN is your body's master clock. It literally is running your circadian rhythm. So while those rods and cones are actually telling you what you're looking at, the IPRGCs are telling your body what time it is. And for shift workers, knowing the time is everything. Now, why are they actually important? It's clear, your body is running on light, it is its main key zekeeper, it's its main timekeeper. Every hormone rhythm depends on the signals from these cells. Everything, every clock in your body, and we now know that every single cell in your body has a time clock in it, every single one of them. And those IPRGCs in your eyeball are actually signaling to the body clock, the master clock, what time it is. So when the IPRGCs get bright light at the right times, things run smoothly. So think about your nine-to-fiver, they get up in the morning, they get outside, they go for their walk, they do their thing during the day, they're out in the light, things are running smoothly. But when you, hello shift workers, get light at the wrong times, everything shifts out of place. And here's what these cells control when you feel alert, when you feel sleepy, when melatonin rises in your body, when cortisol drops, when cortisol rises, when your melatonin drops, how your metabolism runs, how stable your mood feels, whether you feel depressed, whether you feel happy. These cells help set the entire circadian rhythm. And as a shift worker, your rhythm is already seriously challenged. So you have to be even more aware of how these IPRGC cells work because they are super important. So let's look at the light and dark hormone releases. Let's walk through what would happen in a normal day. In the morning, and you've heard me say this over and over again, sky before screen, sky before screen, and there's a reason. The sky that you're looking at outside, when you go out and you get daylight, even on an overcast and a rainy day, it's running at around about 10,000 lux of light. That is the daylight that our eye needs, the blue light. And the reason why I say sky before screen is because the light in your phone is insufficient. Now, while it's too much light at night, it's insufficient blue light during the day to actually reset that circonium rhythm. Weird, I know, but that's how it works. So in the morning, when bright light, as we do, and you've seen me, I lie in bed and I look out the window, open the blinds, look out the window, get outside, take your coffee outside. What happens then is melatonin is actually switched off because those IPRGCs in your eye register, oop, there's blue light as part of the spectrum of white light. There's blue light, it turns off the melatonin, cortisol rises, which helps you to wait to get you going. Your core body temperature then starts to lift, and your brain and body goes, Okay, it's now daytime. Daytime started, and it starts to alert the rest of the body. That's why getting that early light is so important. Your body needs to anchor itself every single day. And the way that it does this is it gets a daytime signal. And the way it gets that daytime signal, when you open your eyes and that light hits those IPRGCs, they deliver that signal to the body's master clock. It's go time. But if morning light is weak or you stay inside, like if you crawl out of bed to the couch and just put on Netflix, your internal body clock just can't start. It does not start properly. And this is when people start to feel really sluggish, you get brain fog, and you end up out of sync. Now, at night, the opposite happens. When it gets dark and those cells stop seeing that blue light, and I want you to hang on to this one. When your those cells, the IPRGC, stop seeing that bright blue light, melatonin starts to rise, cortisol falls, your brain shifts into that night mode, your body goes into rest and digest, and your body gets ready for sleep and to repair itself. And this is the catch. If you expose those IPRGCs to bright light at night, hello mobile phones, tablets, overhead LED lights, TVs in your bedroom, your brain actually gets confused. It's actually thinking it's daytime and melatonin drops. Sleep becomes a lot harder. You don't stay asleep, and your rhythm slides further away from where you actually want it. Now you've got to remember, even if you're lying in bed in the dark and you're watching that screen, that light is hitting those IPRGCs. Anything that's blue is telling your body it is still daytime. And where do we hold our phone? About six inches from our face, we've got blue light going straight into our eye. Now, while it might not inhibit going to sleep, it is certainly having an impact on your circadian rhythm. And I've done a podcast on what the difference is between sleep pressure and regular normal sleep, right? Circadian aligned sleep. Now, why does this matter even more for you, the shift worker? Let's talk about that. Because shift workers live with flipped or irregular light exposure and irregular light exposure. And these cells, they don't understand your roster. They don't look at the roster and go, okay, we're on nights. Oh, we're on days. Okay. All they do is they understand light and they are just signaling to your body light. So if you're on nights and you're blasting your IPRGCs with bright light at 3 a.m. or looking at screens, your brain thinks the day has started. What that does is it makes it harder to sleep later because your circadian rhythm is completely out of sync. Remember, it's indicating straight to the SCN. It's telling your body's master clock, daytime, daytime. And it completely throws you out. Now, when you walk out into strong morning light on the way home, those cells switch off melatonin at exactly the wrong time. This is why many shift workers feel so wired when they actually want to sleep. Now you might go to sleep when you get home, but that's sleep pressure because you've been awake for so long. But will you stay asleep? No. How many people have trouble sleeping when you're on night shift? You're not designed to sleep at that time. The trick is not to fight your biology. The trick is to work with these IPRGCs. Very important. Those cells in your eye, let's work with them. So how can we use them to our advantage? And here are simple and practical rules. On a day shift or an early start, get bright outdoor light as soon as you can. Aim to get at least 10 to 15 minutes. What this does is it anchors your circadian rhythm. As I explained earlier, here's the blue light. Okay, it's daytime. Suppress it all the night stuff. Let's get the day stuff going. When you're on afternoon shift, I still want you to get that morning light because what it does is it keeps your rhythm stable and it won't hurt your night sleep once you get home from work. And when you're on night shift, get light during the night only when you need to stay alert. But avoid blasting your eyes with very bright light. And on the drive home, you need to block that morning blue light with blue light blocking glasses. You want that melatonin to stay high until you get home and can fall asleep. If you're driving home and you haven't got glasses on at all, and that or normal sunglasses, and that blue light is actually hitting your eye, what it's doing is it's suppressing the melatonin and telling your body you don't need to sleep now. It's daytime. Let's go. Now, in the evenings on your days off, you need to dim your lights. You need to use zero blue light bulbs, you need to reduce that screen brightness or not look at screens at all for up to two hours before you go to sleep. You need to give those cells in your eye a clear night signal. Now we've actually swapped all the lights in our house to zero blue lights from block blue light. And anybody that's interested in having a look at those lights, you can go to my website. And at the top, you'll see that there's a link to resources, and underneath that there will be one that says recommended products. And have a look on there, and you'll see the link to the products that I recommend with Block Blue Light. We've gone through our whole house and changed all of the LED down lights to bio lights. And what that means is they are EMF and flicker-free during the day and have the full spectrum of blue in them, and then at night they have zero blue in them at all. And it makes an amazing difference to mood, you're ready for sleep, you sleep so much better. It's incredible the difference that it makes. Those lights in your house are impacting on your health, and it's important that you understand that. And what I also need you to do is to stay consistent where you can. Even small patterns will help these cells to guide your hormones. Literally, anchor your circadian rhythm. When you're on night shift, it's almost impossible to anchor it with daylight. I get that. But every other time you can, and this is why I talk about that regular wake-up time. Now, why isn't this just about sleep? Because people think this is just a sleep issue. But the IPRGCs influence so much more, and I mean so much more. Let's see if you can relate to any of this. They actually affect mood stability. Your appetite. Blue light means daytime means hunger. It helps with the appetite timing, it helps with metabolism. We are not designed to actually eat overnight. Blood sugar control, cognitive function, brain health, brain fog, heart health, the rhythms in your gut. Is it any wonder that you suffer from digestive issues, gas, bloating when you're on night shift? So if your IPRGCs fire at the wrong time, your whole system becomes disordered. And that is why many shift workers feel like their body is constantly guessing. And you know why? It's because it is. Because when you give these cells the right signals, your body feels a lot steadier. And it won't take long to actually feel the difference. I challenge you for one week to try getting up at roughly the same time every morning. And this is why I say getting up at the same time every day. Bonus points for getting to bed at the same time. But even after a late night, getting up at the same time and anchoring that circadian rhythm with light is what will get you thriving. And you now know why. It's because of those IPRGCs. You need to get that light into your eye early and anchor that circadian rhythm to improve everything. And as I said, mood stability, appetite timing, your metabolism, your blood sugar control, cognitive function, brain fog, heart health, cardiovascular health, gut rhythms. All of this makes a huge difference by just anchoring that circadian rhythm. Understanding these IPRGCs, one of the most powerful things that you can actually do as a shift worker, you have very, very limited control over your roster. I get that. But the one thing that you do have control over, and I always say control the controllables, is you control your light exposure. Now, these cells do not care about your job. What they do care about is light. So give them the right signals, and your body will actually respond so much better. So thanks for listening to a healthy shift podcast today. I really hope you got a lot out of that one. And if you want support with getting your light routine right, you can reach out to me through the show notes. There's a link there. Let's have a chat. I can help you. So take care and I'll talk to you again on the next one. Thank you for listening. If you enjoyed this episode, be sure to subscribe so you get notified whenever a new episode is released. It would also be ever so helpful if you could leave a rating and review on the app you're currently listening on. If you want to know more about me or work with me, you can go to ahealthyshift.com. I'll catch you on the next one.