How Do You Nurture Your Circadian Rhythm?

We have already talked about how a broken circadian rhythm puts you on a slippery slope to bad health and – worse – to diabetes. Let’s discuss which everyday habits nurture a healthy circadian rhythm.

When (and How) You Wake Up Is the Most Important Event of the Day

When you wake up, open your eyes, and get out of your bed, that first ray of bright light entering your eyes activates the melanopsin light sensors in your retina that tell the SCN master clock in your brain that morning has arrived. Just like in a spy movie when two agents begin their mission and synchronize their watches, seeing the first ray of bright light signals the SCN to set its own clock time to the morning. (The SCN clock also synchronizes the day from the previous sunrise, so it will wake us up around the same time the next day.) Usually, when the SCN clock registers morning, it will automatically nudge you to wake up – like an internal alarm clock. But if you need a real alarm clock to wake yourself up, your SCN isn’t ready and still thinks it is night. This is why the goal is to be less reliant on an alarm clock and to get enough hours of sleep so that you wake up when your SCN recognizes morning.

As you fill in the chart below, note not only what time you woke up but if you required an alarm clock. We don’t wake up the same way our ancestors did even a century ago. In the past, when our circadian clock was in sync with the day-night cycle and we went to bed before 10:00 p.m., our SCN clock would wake us up around dawn. That’s when we naturally stop producing melatonin and our sleep drive decreases. Dawn also brings many environmental signals to wake us up, like the first light and the noises of birds and other animals. If those cues didn’t do the trick, a rise in body temperature would wake us up; as melatonin levels drop to reduce drive to sleep, cortisol levels go up, making us feel noticeably warmer.

Today, we rarely wake up to these cues. Sleeping in a perfectly temperature-controlled bedroom with double-paned windows covered with thick curtains or blackout shades, we’ve all but cut out the natural morning signals of sound, light, and temperature. And when we go to sleep late, our sleep drive and melatonin levels are still high at dawn. This is why so many of us require a bone-jarring alarm clock.

Your First Bite/Sip of the Day

Just like the first sight of light syncs your brain clock with light, the first bite of food signals the start of the day for the rest of the clocks in your body. In our research, we found that 80% of people eat or drink something other than water within an hour of waking up. The next 10% have something within two hours, and only a small fraction waits for more than two hours to eat. Many people also reported that they often skip breakfast. These numbers just didn’t add up, so we dug deeper and found out that the term “breakfast” is widely misunderstood.

Breakfast means “breaking the fast”, or the time that passed the night before, when you weren’t eating or drinking. But what constitutes a true break of a fast? The answer is whatever triggers the stomach, liver, muscles, brain, and rest of the body to think the fast has been broken. And that answer is almost anything you put in your mouth besides water.

You may think that a small cup of coffee with a little cream and sugar is not going to break your fast; most people simply associate their morning brew with an attempt to wake up the brain. Actually, as soon as we put calories in our mouth, our stomach begins to secrete gastric juice in anticipation of digesting food. Then a cascade of hormones, enzymes, and genes start their regular chores. That first cup of coffee or tea – if it contains calories in the form of milk or cream or sugar – is all it takes to reset the stomach and brain clocks.

Most of our respondents consumed less than one-quarter of their total daily intake of calories between 4:00 a.m. and noon, while they ate more than 30% of their daily intake at night. They reported that they were skipping breakfast, but in reality, they were just skipping a big meal in the morning.

Instead, they were eating a small snack of coffee/tea/juice/yogurt/etc., which they didn’t consider a meal. However, your stomach does consider it a meal. It does not matter whether it is a cup of milky coffee or a whole bowl of cereal when you break your fast. In either case, write down the time.

If you still have questions about what should count as food, just think about the day you do your fasting blood glucose test first thing in the morning. Does your doctor tell you it is ok to drink a cup of tea or coffee before taking your blood glucose reading? Usually, the answer is no.

The End of Your Last Meal/Drink

Just like your brain must switch from being active during the day to resting and rejuvenating at night, your metabolic organs also need to wind down and rest for many hours. The last bite or last sip of the day signals our body to prepare to wind down, cleanse, and rejuvenate. It takes a few hours for the brain and body to get the message and start the process; it needs to be completely sure that no more calories are coming its way. So, just like a cup of coffee starts your metabolic clock, your last bite of food or drink has to be part of the digestive process for three to five hours before the body can begin its repair and rejuvenation mode.

Culture is one of the biggest predictors of eating patterns. Although many people in the United States eat dinner early, we live in a culture of after-dinner and late-night snacking. In many Eastern countries and in parts of Europe, late-night eating is the norm. In some countries, restaurants don’t even open for dinner before 9:00 p.m. In some places, late-night dinner is the biggest meal of the day, while in others it is usually a small meal or leftovers from lunch.

Be honest and write down when you took your last bite or last sip (other than water and medication) of the day. You may go into this exercise thinking that you already have a schedule, but my research shows that it is likely that you don’t. We use food to keep us energized or to unwind. The weekends pose a different challenge, as we are often on a completely different schedule, socializing well into the night. Keeping track will show you clearly whether you’re adhering to a pattern.

When Do You Go to Sleep?

This is again a difficult question to answer. Wake-up time is relatively fixed by your work schedule, so your bedtime often determines how many hours of sleep you’ll get. Some of us have a fixed schedule during workdays. Some may have a fixed bedtime every day but wake up at different times on workdays and off days. The most accurate answer is the time when you have shut off lights, checked your last e-mail/text/social media account, and are in bed with your eyes closed.

What time Do You Shut Off All Screens?

With 24-7 social media, television, and streaming entertainment on digital devices, it becomes important to know when you turn off the virtual party. You may be thinking that watching TV and being engaged in social media is a way to unwind and relax. But pay attention to whether they make you more stressed and jazzed up, which they often do.

Once we shut off our devices, our brain takes many minutes to unwind. Our eyes receive a big share of light from digital screens, so turning off the screen is also signaling when we turn off all light input to our brain.

What Time Do You Exercise?

There are distinct effects of time of exercise or intense physical activity on circadian rhythm, sleep, and your blood glucose level. So, what time you exercise matters. We will cover this topic in more detail elsewhere.

• Gill and S. Panda, “A Smartphone App Reveals Erratic Diurnal Eating Patterns in Humans That Can Be Modulated for Health Benefits,” Cell Metabolism 22, no. 5 (2015): 789–98.
• J. Gupta, V. Kumar, and S. Panda, “A Camera-Phone Based Study Reveals Erratic Eating Pattern and Disrupted Daily Eating-Fasting Cycle among Adults in India,” PLoS ONE 12, no. 3 (2017): e0172852.