The human body follows a circadian rhythm that allows us to follow a healthy routine. Commonly known as the internal clock, it consists of a 24-hour schedule that tells your body when to sleep and wake up. It also influences the production of hormones and controls body temperature. Now, research has shown that your circadian rhythm also influences the immune system, thereby helping manage inflammation better.
The Time-of-Day Influences When Inflammation Occurs
In a study published in The FASEB Journal,1 researchers investigated how the body’s internal clock plays a role in managing inflammation by way of the immune system. Specifically, they discovered that macrophages, a specific type of immune cells, behave differently at various times of the day.
When activated, macrophages trigger inflammation as a defense mechanism by creating inflammasomes. At the center of this process is the NLRP3 inflammasome, which is responsible for “processing and releasing inflammatory cytokines, such as interleukin-1β (IL-1β), to amplify inflammation.”2
To conduct the study, the researchers used an animal model and subjected the participants to opposing 12-hour light-dark cycles for two weeks before being covered in constant darkness for 24 hours. This methodology allowed them to analyze the impact of their internal clock on immune function and subsequently, on inflammation.3 A report from Medical Xpress summarizes the findings:4
“Activation of an inflammasome called NLRP3 was not found to be constant throughout the day but was regulated by the body’s 24-hour circadian clock. This daily rhythm determines when macrophages are most efficient at detecting threats and when their energy levels peak to mount a response. The research also highlights a key role for mitochondria, the cell’s energy producers, in driving these daily changes in immune activity.
When macrophages ‘think’ it’s morning, their inflammasome activation is quicker and more robust,” explained Professor Annie Curtis, principal investigator for the study at RCSI School of Pharmacy and Biomolecular Sciences. “This means the immune response is heightened during the early part of the day, a time when we are awake and more likely to encounter environmental challenges, such as injuries or infections.”
This discovery highlights how administering treatments at a specific time of day will have an impact for patients suffering from inflammatory diseases. One example is arthritis, wherein its symptoms usually worsen during the morning. According to Dr. James O’Siorain, the study’s lead author:5
“With these findings, there’s potential to refine treatments for inflammatory conditions. For instance, new therapies targeting inflammasomes could be more effective if administered at specific times of the day when macrophage activity peaks.”
Light and Dark Exposure Impact Your Circadian Rhythm the Most
According to the Cleveland Clinic, light and dark have the biggest impact on your circadian rhythm.6 Therefore, syncing it into a regular schedule is important. However, advances in technology have largely impacted most people’s circadian rhythm in the name of convenience or productivity.
For example, after electric light bulbs were invented, night shift work began as humans found a way to extend “daylight” hours.7 The introduction of computers, tablets and smartphones have also exposed countless people to blue light at night at an unprecedented level. Blue light disrupts your ability to fall asleep as it tells your brain to stop producing melatonin.8
This disruption to your circadian rhythm, which is stabilized by bright light exposure during the day and complete darkness at night, takes a toll on your health. Increased exposure to light during nighttime is linked to an increased risk of several psychiatric conditions, including:9
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Major depressive disorder |
Generalized anxiety disorder |
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Post-traumatic stress disorder (PTSD) |
Psychosis |
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Bipolar disorder |
Self-harm behavior |
In one study, researchers noted that being exposed to any amount of light during nighttime is detrimental to older adults. Specifically, it increased their risk of obesity, high blood pressure and diabetes.10 In another study, higher exposure to outdoor light at night increases the risk of postmenopausal breast cancer,11 and evidence suggests light at night may increase thyroid cancer risk, too,12 as thyroid function is regulated by the circadian rhythm.
Get Your Circadian Rhythm Back on Track with Proper Light Exposure
Andrew Huberman, a neuroscientist and tenured professor in the department of neurobiology at Stanford University School of Medicine, recommends viewing bright light, ideally from sunlight, within the first 30 to 60 minutes after waking to stimulate wakefulness throughout the day and help you fall asleep at night.13
In addition, research shows that viewing light during the early hours of the evening will help mitigate some of the consequences of light exposure later in the evening.14 However, when it’s 6 P.M. or 7 P.M., it’s important to avoid bright artificial lights of any color. As mentioned earlier, devices emit blue light that block melatonin production as it tricks your body into thinking it’s still bright.
Once the sun goes down, make it a habit to dim the lights around your home and use as little artificial light as possible. This includes turning down your computer screen and avoiding overhead lights, opting for desk lamps instead. If possible, use candlelight or moonlight only after sunset.
If your bedroom is affected by light pollution, be sure to use blackout shades to keep light out and remove all sources of light from your bedroom, including a digital alarm clock or cellphone. Another alternative is using a sleep mask.
Timing Your Meals Will Also Sync Your Internal Clock
Timing your food intake will reset your peripheral internal clocks, particularly in metabolic organs like your liver and pancreas. That’s because eating times influence peripheral clocks even in the absence of light cues.
This was observed in one study,15 wherein researchers looked at how delaying meals by five hours impacted various body clocks and biological markers. Ten young men adhered to a 13-day schedule eating three meals (breakfast, lunch and dinner) at five-hour intervals, either starting soon after waking (early meals) or later in the day (late meals). After adjusting to early meals, the participants switched to late meals for six days.
The researchers observed that blood glucose rhythms were delayed by about 5.7 hours when meals were delayed, and that average glucose levels dropped. This indicates that meal timing helps synchronize peripheral circadian rhythms.16
In another study,17 researchers investigated if eating meals earlier in the day affects the body’s heart-related circadian rhythms and blood lipid levels. They selected 14 young adults who typically skipped breakfast, separating them into two groups.
One group ate meals at 8:00 a.m., 1:00 p.m., and 6:00 p.m., while another group ate five hours later, at 1:00 p.m., 6:00 p.m. and 11:00 p.m. After analysis, they observed significant decreases in triglycerides, total cholesterol and LDL cholesterol in the group who ate earlier compared to those who ate later.
While high total cholesterol and/or elevated low-density lipoprotein (LDL) cholesterol do not cause heart disease, the study still shows the profound influence that meal timing and circadian rhythms have on cholesterol synthesis. This information is also important for those following time-restricted eating (TRE).
If you’re metabolically inflexible, short-term fasting will be helpful in resolving obesity and insulin resistance. Once you regain your metabolic flexibility, which takes anywhere between several weeks to a few months, you will need to increase your eating window.
The reason for this is because when you deprive your body of glucose for too long, it will produce cortisol to stimulate your liver to make glucose. Cortisol is also a stress hormone, which isn’t what you want circulating throughout your body for extended periods of time.
Elevated cortisol levels contribute to chronic inflammation and cellular damage. Therefore, once you are no longer insulin-resistant, it is best to mix up your eating window between 12 to 18 hours, with longer hours in the winter and shorter in the summer. It is also wise to avoid eating before sunrise or after sunset and having your last meal at least three hours before bedtime.
Your Sleeping Routine Also Influences Your Circadian Rhythms
Beyond optimizing light exposure throughout the day and timing your meals, other factors such as getting enough sleep and keeping a regular sleep schedule, also affect your body’s internal rhythms.
Going to bed and waking up at the same time every day, even on weekends, reinforces your circadian rhythms. Engaging in regular physical activity,18 especially during daylight hours, also helps. Your circadian clock function is also closely connected to your body’s stress response system,19 which is why practices such as mindfulness, meditation and relaxation techniques that help manage stress can also help sync your circadian rhythms.
For strategies on how to get better, read “How Sleep Deprivation Impairs Cognitive Performance and Learning.” There, I discuss a multitude of useful tips, such as employing stress-reduction techniques and exercise to improve sleep quality.
