Pay attention to your body’s master clock
For the past 10 years, I’ve been studying chronobiology, the timing of biology. I’ve gotten to explore this field through endocrinology and neuroscience. All my experiments have been in a lab.
To design my latest experiment, I found myself on a rooftop at 3:00 AM watching an elevator rescue. Then 20 minutes later, I was speeding down the street in a fire truck. Those were two of eight calls that we went on between 10:00 PM and 6:00 AM, all so I could understand the demands of a 24-hour shift schedule on firefighters.
At the end of that ride along, I went home, and I went to sleep. At the same time, a lot of firefighters on call that night were just starting their next 24-hour shift.
As a researcher here at Salk, I’m now applying my knowledge of chronobiology to help a wide variety of individuals, including firefighters, to help prevent and treat disease.
I’ve been in the field of chronobiology for a while. I’m still blown away by the importance of timing of biology, and the beautifully intricate system that regulates it. It so astonishes me that as a society we’re largely unaware of, and thus ignore, our biological clocks.
Circadian is Latin for about a day. We use the term Circadian rhythms because in almost every living organism, we see clear 24-hour patterns at every level of biology. It includes behavior, physiology and even individual cell function.
In humans, when we think of behavioral rhythms, the first thing that comes to mind are sleep and wake cycles. We also have rhythms in our mood, cognition and learning. We even have daily patterns in the language that we use, our concerns and our emotions.
At the physiological level, pretty much anything that you would get tested at the doctor’s office has a Circadian rhythm. For instance, your heart rate and blood pressure naturally rise in the afternoon and are lowest while you sleep. You have a peak of triglycerides in the morning. Due to these daily changes, it’s a pretty good idea to schedule your doctor’s visits for the same time of day every time.
All these changes and physiology in behavior all stem from rhythms in individual cells. If you look at it collectively, mentally and physically you’re a different person at different times of day.
All of these rhythms come from within you. If I stuck you in a constant environment, those rhythms would still persist. That’s not the world that we live in. So, our body also looks for cues like light and food to coordinate with the world around us. It’s this combination of your body’s internal rhythms with external cues from the environment that determine our rhythms in physiology and behavior.
How do we do this? Almost every cell in your body has a molecular clock that keeps about a 24-hour rhythm. I say about because each one keeps slightly different time. So, you need something to coordinate them. To do this, we have a master clock in our brain called the superchiasmatic nucleus, or SCN for short. It’s a complicated name for where it’s located.
What you’re watching is a video from the SCN of a mouse brain with a fluorescent tag attached to a piece of the molecular clock. Every time that piece of the clock is made, it lights up. This video was taken over many days, but one full wave is about 24 hours.
Not only does the SCN coordinate all these clocks throughout your body, but it also incorporates external cues from the environment. It’s this coordination that allows our body to prepare for the day ahead. It helps us be alert when we wake up. It has our digestive system ready to process food when we eat. It helps our organs rest and repair while we sleep.
The two biggest cues you can give your body to tell it the time of day are light and food. Evolutionarily, those were very reliable cues to know the time of day. Unfortunately, in modern society, light and food are available and taken advantage of around the clock. This can lead to Circadian disruption.
Circadian disruption occurs when those internal Circadian clocks are challenged by conflicting external cues. The most common examples are shift work and jet lag.
Over 20% of the U.S. population does shift work. Each schedule is a little different, but they all face abnormal patterns in sleep, eating and activity. They’re the crux of our society. They keep everything going. Our newscasters, cleaning crews, chefs, construction workers and journalists.
The heroes of our society, the firefighters, police officers, doctors, E.M.T.s, nurses and military take the hardest schedules that are mentally and physically challenging, just to support our community.
Yet, unfortunately, shift work is linked to a wide variety of diseases. In fact, the World Health Organization actually lists shift work as a carcinogen. Yet there’s still no way to stop these risks from increasing and keep doing harm.
You may not do shift work, but I’m guessing that everyone here has been jet lagged. I’m not just talking about that first day of sleep deprivation. I’m talking about those following days of muscle weakness, nausea, moodiness, fuzzy thinking and exhaustion at seemingly random times of day. That’s a feeling of Circadian disruption.
This is because our bodies were not meant for airplane travel. For every hour that you make your body shift, it takes about a full day to catch up. If you fly from San Diego to Paris, a nine hour phase shift, it’s going to take your body about 8 to 10 days to get there.
On that first day when you’re having breakfast, your body thinks it’s time to go to bed. On that last day when you’re about to fly home, and you’re finally feeling good again, you’re going to make your body shift all over again.
Unfortunately, Circadian disruption is not limited to shift work and jet lag. Our society has become exceptional at ignoring and disrupting our body’s natural rhythms. It can start with something really simple.
Say it’s a Friday night, and you’ve had a really long week. All you want to do is come home, relax and just let it ease off. So, you eat. Then it’s time to binge watch your favorite TV show. Then you’ll need a drink or a snack to go with it. The show is very good, so you’ll need another drink.
Before you know it, it’s one or two in the morning before you finally put that last drink or snack down. That sounds like a great Friday night. Unfortunately, Monday rolls around, and you’re back on your regular schedule.
You might be waking up two or three hours earlier than you did on the weekend. It’s a very common story. It’s a very common way in which we naturally disrupt our body’s rhythms.
In fact, it’s so common that there’s actually a term for this. These really large shifts between our weekdays and weekends, free days and work days, are actually referred to as social jet lag.
Your body may be in the exact same city, but it feels like it’s traveling back and forth between two or three time zones every weekend. It’s like going from San Diego to New York or Mumbai to Tokyo.
Chronic Circadian disruption has wide impacts on your health. The Circadian system is linked to every level of physiology. Disrupting those rhythms can lead to an increased risk for a wide variety of diseases including reproductive disorders, metabolic disorders such as diabetes, cardiovascular disease, cancer, neurodegenerative disorders and mental health issues such as bipolar and depressive disorders. In fact, our lab came up with a list of over 100 diseases that are linked to Circadian disruption.
What are we going to do about this? As I said, light and food are the two biggest external cues you can give to your body to tell it the time of day. Light talks directly to that master clock in your brain, the SCN. Food talks directly to all the other clocks in your body.
Research is ongoing, but this is what we know so far. You need to keep your body on its schedule, so it can prepare itself for what it needs to do. This means using those external cues to support your biological clocks. Tell it when it’s morning and when it should be awake. Decrease stimulation at night so it can get a proper rest.
First, let’s talk about light. We’ve all probably heard of the role of light in sleep. In the morning, you need to get lots of bright light. I’m not talking about office light. I’m talking about natural sunlight.
You can easily do this by taking a 10-minute walk outside. If the only light that you’re going to get is on your commute to work, and the sun isn’t hitting you directly in the eyes, try not wearing sunglasses.
At night, to tell your body it’s time to rest, dim or turn off lights that you’re not using. If you’re going to be looking at a computer, phone or tablet, try using a blue light filter.
What I’m really excited to talk to you about today, and what all of my research is pretty much currently focused on, is the timing of food. Don’t get me wrong. What and how much you eat is extremely important for your health, but recent studies have found that when you eat is just as important.
Your body needs at least 12 hours of fasting every day to function properly. Our lab uses a smart phone app called My Circadian Clock to understand when people eat.
In one of our recent studies, we found that individuals have an average eating interval of 15 hours a day. That’s 9 hours of not eating. That means if your eyes are open then your mouth is open.
Recent studies have found that time restricted eating, which only changes when you eat, not what you eat, can improve glucose tolerance and insulin sensitivity. It can lead to about a 5% weight loss. It improves endurance and decreases blood pressure.
How does changing when you eat have such a big effect? First, your body has a natural rhythm in glucose regulation. It interprets food differently at different times of day. A bowl of ice cream at noon is going to be much easier for you to digest than it is at midnight.
Secondly, as I said, you need 12 hours of fasting so your body can properly rest and repair. When you’re continuously taking in new calories, you break up that rest. You never get to break down the energy stores that you already have. That means that you never burn fat. Over time, this can lead to weight gain and eventually to diseases like diabetes and cardiovascular disorders.
Finally, food is a wake-up cue to the brain. You’ll fall asleep after that late night drink, a snack or heavy meal, but the quality of sleep that you’re going to get is going to be greatly decreased.
Time-restricted eating is a simple lifestyle change. Eat within the same 10-hour window every day. That’s it. If the first thing you have is at 8:00 AM, then the last thing should be at 6:00 PM.
The exact time of day is going to depend on your schedule and your preferences. The only restriction is that you leave at least 3 hours before you go to bed of only water so that your body can get that proper rest.
I realize that a lot of you just did some mental math. I’m probably not your favorite person right now because you may have just interpreted what I said as, if you want to be healthy you can no longer have a social life, get drinks, or you are only going to have to day drink all the time. That’s not completely true.
What I’m saying is, timing matters. When you eat is just as important as what and how much. The same way that you should eat a healthy meal every day, you should also eat it when your body expects it. Give it at least that 12-hour rest.
Of course there are going to be cheat days. That is completely fine. The same way you eat cake. You might end up eating it at night. It’s okay. Awareness is really the issue. Acting like the timing that you eat doesn’t matter is like thinking French fries are just as healthy as broccoli.
I went on that 24-hour ride along because I’m designing an experiment to help test the benefits of time-restricted eating on firefighters on a 24-hour schedule. They can’t change when they get a call or when they get a chance to sleep. Changing something as simple as when they eat may have long term benefits on their health and make those 24-hour shifts a lot easier.
The Circadian system is the pillar of health that, for far too long, has been ignored or misunderstood. We now know that with simple non-invasive lifestyle changes, we can support our biological clocks to optimize performance, delay the onset of age-related illnesses and prevent and treat disease.