Your circadian rhythm determines the timing and accuracy of the internal body clock that helps you fall asleep at night and wake up with the morning light. But that’s just the tip of the iceberg.
Working at a cellular level, the circadian system produces 24-hour rhythms that orchestrate countless body systems — everything from metabolism, to the function of the heart and blood vessels, to cholesterol synthesis, inflammation, and other processes.
When these rhythms are functioning properly and your body is aligned with the optimal light-dark cycle, you enjoy good circadian health. When your rhythms get knocked off kilter by external or internal disruptions, the ripple effects on your health can be wide-ranging.
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What controls your circadian rhythm?
Your brain houses a central clock, located in a tiny structure of the hypothalamus called the suprachiasmatic nucleus (SCN). It contains more than 10,000 “pacemaker” neurons and, through the coding of “clock genes,” it regulates the circadian rhythms and the many peripheral clocks found in tissues and organs throughout your body.
The SCN is activated by light hitting the retinas of your eyes, which prompts it to send out neural and hormonal signals to the peripheral clocks. It can also be affected by the timing of other things such as when you eat and exercise.
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What do circadian rhythms control?
Circadian rhythms regulate the ebb and flow of a range of functions and the daily rhythms of the lungs, liver, heart, and other organs. The list of impacted bodily systems is long and includes:
- Blood pressure
- Heart rate
- Appetite
- Body temperature
- Insulin sensitivity
- Function of blood vessels
- Alertness
- Carbohydrate and lipid metabolism
- Inflammatory processes
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What disrupts normal circadian rhythms?
Exposure to light at night can cause significant disruptions to natural circadian rhythms. Darkness serves as an important cue to the body’s clock; it’s what signals the production of melatonin, a natural hormone that readies the body for sleep. When the lights stay on past sundown, our “night timeline” is pushed back, delaying melatonin production and bedtime and the many processes that happen while we sleep. Other factors that knock circadian clocks out of sync include:
- Late-night eating
- Sleep-wake disorders
- Night shifts or rotating work shifts
- Exercise in the evening
- Certain diseases
- Day-to-day variability in your sleep schedule
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What happens when circadian rhythms are out of sync?
Research shows that circadian rhythm disruptions, common among shift workers or those who are frequently jet-lagged, can increase the risk of a number of conditions and diseases. One recent large-scale study found that irregular sleep rhythms, like sleep fragmentation and inconsistency with bedtime and wake time, were associated with a higher risk of 172 diseases.
Even subtle shifts in sleep timing — going to sleep at 10 p.m. on a weekday, but midnight on a weekend — can have negative effects on your circadian rhythms and your overall health. One study found an hour of increased variability in sleep timing was associated with 25% higher odds of having obesity around the abdomen, a risk factor for heart disease.
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What does a circadian rhythm problem look like?
Possible consequences of circadian rhythm problems include:
- Weight gain and/or obesity
- High blood sugar levels and diabetes
- High blood pressure
- Coronary artery disease
- Major cardiac events
- Neurodegenerative diseases
- Mood disorders
- Cognitive decline
- Cancer
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Learn how to keep your circadian clocks in sync.
Circadian health is important — and fairly simple. The closer you can align your sleeping and waking cycles to nighttime darkness and daytime light, the better your circadian health will be. Be sure to get adequate exposure to sunlight during the day, ideally stepping outside not long after waking in the morning. Dim the lighting about two to three hours before bedtime, and be careful about exposure to blue light from screens.
Eating and exercising late at night may also keep the SCN stimulated, so moving these activities earlier may help keep your circadian rhythms steady. Pay attention to caffeine and alcohol intake, as these things can interfere with the body’s natural sleep cues.
