Circadian rhythm refers to the 24-hour cycle that regulates bodily functions, from sleeping to waking. Also known as the internal body clock, the circadian rhythm is directly tied to the suprachiasmatic nucleus (SCN) in the hypothalamus, which coordinates the timing of biological events, like hormone release, body temperature, sleep, and digestion. Your circadian rhythm dictates sleeping patterns, blood pressure, blood sugar, melatonin levels, and general alertness. This internal clock is heavily influenced by your environment and can be disrupted by time zone changes, pregnancy, lighting, napping, and irregular work schedules.

Circadian rhythm can affect your sleep due to the activity of the SCN. Located above the optic chiasm (the nerves that connect your brain to your eyes), the SCN uses the light entering your eyes to determine how much melatonin it secretes. When it is darker outside, your body secretes more melatonin, which makes you feel drowsy. If your circadian system is out of balance, your body may receive more melatonin during the day, which can lead to disturbed sleep-wake cycles or certain sleep disorders.

Circadian rhythm disruptions can be the result of various factors, such as:

• Light: Light is the biggest disrupter to your internal body clock, which is why it’s harder to fall asleep when in daylight and why you shouldn’t use electronics right before bed. Bright light can confuse your inner clock into thinking it’s daytime, which can cause your body to secrete less melatonin, resulting in less sleepiness at bedtime.
• Time: Traveling across time zones can cause jet lag, which happens when your circadian rhythm has yet to adjust to the time difference of a new location. Shift-work disorder can also disrupt internal rhythm, as those who work night shifts and sleep during the day are going against the natural light-dark cycle, which can be a hard adjustment for the body to make.
• Mood disorders: People with bipolar disorder or depression have an imbalance in their serotonin secretion. When your body cannot properly regulate its serotonin levels, it can trigger phase shifts in your circadian rhythm, affecting mood and appetite and causing irregular sleep patterns. In turn, an imbalanced circadian rhythm can exacerbate these irregularities, leading to a cycle of disruption that becomes harder to reset.
• Long naps: Napping can completely throw off your sleep-wake rhythm. While short, 10- to 20-minute naps early in the afternoon can help you feel more refreshed, napping longer and later in the day makes you more likely to fall into a deep, NREM sleep, making it difficult to fall asleep naturally later on.
• Food: When you eat, your body releases insulin. This hormone carries glucose from your blood into your muscles and other organs, which your body uses for energy. Blood sugar levels typically spike during the night but eating right before bed can lead to an even higher spike. Your kidneys work overtime to help remove the sugar from your blood, which can result in frequent urination during the night, disrupting your healthy sleep.

While it can be hard to break out of poor biological rhythms, there are a few things you can do to help improve your internal clock:

1. Create a sleep schedule. One of the easiest ways to improve your circadian rhythm is to go to bed at the same time every night. Establishing a consistent sleep schedule can help regulate your sleeping habits, significantly improving your circadian rhythm.
2. Limit stimuli. Make sure your room is dark and quiet when you’re ready to sleep. Limit light exposure (like closing the blinds or turning down the brightness on your phone) to create a soothing atmosphere for your brain and body to relax.
3. Exercise earlier in the day. Exercising timing is a great way to improve your circadian rhythms and promote wakefulness. Exercising during the morning or early afternoon hours can help improve your circadian rhythm by advancing your internal clock, making it easier to wake up and begin your daily activities. Exercising later at night can be too stimulating and confuse your natural rhythm, making it harder to fall asleep.
4. Avoid caffeine. Caffeine can keep you awake and alert, but consuming it later in the day can affect your body’s ability to relax and wind down for the night.
5. Bright light therapy. Some people with circadian rhythm sleep disorders and seasonal affective disorder use bright light therapy to help delay their biological clock and regulate their sleep patterns. With this treatment, light is delivered directly to the retina right after waking, stimulating the hypothalamus and helping reset your internal body clock.