Although you won’t hear it tick, your body has its own clock. The physical and mental changes it causes are called circadian rhythms. Most living things have them, including animals, plants, and even some germs.
Circadian rhythms affect your sleep patterns as well as other ways your body works, like your hormones, body temperature, and eating habits. When they get out of sync, they might also cause problems with your health. They’ve been linked to different disorders including diabetes, obesity, and depression.
To get good, healthy sleep, it helps to know what keeps your body’s clock on track and what might throw its rhythm off. The internal body clock sets the timing for many circadian rhythms, which regulate processes such as:
sleep/wake cycles = hormonal activity, body temperature, rhythm of eating and digesting.
Different Patterns for Different People
You’ve likely noticed that you feel more alert during certain parts of the day and have lower energy at others. This pattern has to do with your “chronotype,” or personal circadian rhythm. They vary from person to person, although they tend to run in families.
Most of the time, people fall into one of two groups:
Early birds: If you find it easy to wake up in the morning and feel you have the most energy early in the day, you’re a morning person or a “lark.” Some research suggests that an early bird’s body clock may run slightly faster than 24 hours.
Night owls: If you’re an evening person, some research suggests that your body clock runs slower than 24 hours. You’ll find it hard to wake up in the mornings and feel alert. You’ll have the most energy much later in the day, like 11 p.m.
Your chronotype isn’t set in stone, though. Circadian rhythms naturally change as you age. For example, the body clock shifts during adolescence, making teens want to go to bed later and sleep longer than younger kids.
Your work or school schedule may mean that you need to switch from a night owl to an early bird. You can try to alter your circadian rhythm yourself, but do it slowly. For example, try waking up 15 minutes earlier each morning over the course of a week.
How Circadian Rhythms Work
Within the circadian (24-hour) cycle, a person usually sleeps approximately 8 hours and is awake 16. During the wakeful hours, mental and physical functions are most active and tissue cell growth increases. During sleep, voluntary muscle activities nearly disappear and there is a decrease in metabolic rate, respiration, heart rate, body temperature, and blood pressure. The activity of the digestive system increases during the resting period, but that of the urinary system decreases.
About 20,000 nerve cells make up your “master clock,” a part of your brain called the suprachiasmatic nucleus. This structure, which sits inside an area called the hypothalamus, controls your circadian rhythms. While largely guided by your genes and other natural factors inside your body, things in the outside world can also alter them.
Hormones secreted by the body, such as the stimulant epinephrine (adrenaline), are released in maximal amounts about two hours before awakening so that the body is prepared for activity.
The biggest cue is light. Your body is wired to sleep when it’s dark and stay awake when it’s light outside. Nerves directly link your eyes and your body’s master clock. When daylight fades, your eyes signal your brain to make more melatonin, a hormone that makes you feel sleepy. And when the sun rises again, the signals tell the brain to turn down the melatonin.
Melatonin is secreted by the pineal gland, especially in response to darkness, and has been linked to the regulation of circadian rhythms.
Millions of Americans take melatonin to fall asleep. It’s one of the most used supplements in the U.S. But to get the most from it, it helps to understand how it works and what it can and can’t do for you.
What Is Melatonin?
Before you start taking melatonin, ask your doctor how it could affect other medicines you take!
Screen time. Any amount of light signals tells your brain that it’s time to be up and alert. Even the blue light from your tablet, smartphone, or TV has this effect. To get a good night’s sleep, unplug from all screens 2 to 3 hours before bed. Other artificial light can have the same effect, so turn off hallway lights and face your alarm clock away from you. If you’re bothered by light outside your home, put up blackout curtains or use a sleep mask.
Your period. Many women notice that they sleep worse before their period starts. This may be due, at least in part, to a change in circadian rhythms. Some studies show that less sleep during this time can reset your body clock and give some relief. Bright daylight or light therapy may also make a difference.
Your melatonin level usually starts to rise after the sun sets, and stays high during the night. It drops in the early morning, which helps you wake up. That quality — rising at night, disappearing during the day — gives melatonin its nickname: the Dracula of hormones.
What Are the Drawbacks?
If you take melatonin at the wrong time, it will throw off your body’s internal clock.
You may be tempted to take more melatonin to get sounder sleep, but too high a dose can also cause those side effects, which could disrupt your sleep even more. Don’t try to take more than you need.
You shouldn’t use melatonin if you:
– Are pregnant – Are breastfeeding – Have an autoimmune disorder – Have a seizure disorder – Have depression
Should Kids Use It?
Melatonin may help children with conditions such as autism and ADHD get better sleep, but that’s a decision a pediatrician should approve.
It seems to be pretty safe as a short-term sleep tool, but scientists don’t know a lot about how it might affect kids who take it for a long time. The supplement may also cause side effects, like drowsiness and the need to pee more at night. So always talk to your child’s doctor before you give melatonin.
Circadian Rhythms Out of Sync
Small changes can upset your circadian rhythms. These include:
Travel. When you pass through time zones, you can adjust your watch but not your body clock. It will try to function on the time it is at your home, a problem you may know as jet lag. The more time zones you pass through, the more off you may feel. Your body clock will reset to the new time you’re in, but it can take a few days. To deal with jet lag, take melatonin when you arrive at your destination at the time you’d like to go to bed. Some studies have found that taking it as early as 3 days before your trip can help jet lag symptoms. Keep in mind, though, that melatonin is best when you’re traveling east. There’s no evidence that it helps you adjust to westward travel.
Night shift. If you work the night shift, take it at the end of your workday, but never before you drive home and if you work nights, you’ll need to sleep during the day. This can be tough since your body is programmed to be awake when it’s light outside. Over time, you can start to have what’s called shift work disorder. You’ll find it hard to stay awake at night, yet struggle to sleep during the day. Naps during the day or your night shift can help.
Extra sleep. Your body clock works best when you stick to a schedule. In an ideal world, you’ll go to sleep and wake up within a half hour of the same time each day, even on weekends.
Circadian rhythm in adults
Adults should have a pretty consistent circadian rhythm if they practice healthy habits. Their bedtimes and wake times should remain stable if they follow a fairly regular schedule and aim for 7 to 9 hours of sleep every night. Adults are likely get sleepy well before midnight, as melatonin releases into their bodies. As adults, we reach our most tired phases of the day from 2 to 4 a.m. and 1 to 3 p.m.
Older adults may notice their circadian rhythm changes with age, and they begin to go to bed earlier than they used to and wake in the wee hours of the morning. In general, this is a normal part of aging.
How to reset your circadian rhythm
You may experience disruptions to your circadian rhythm, but you can get it back on track. Here are some tips for promoting a healthy 24-hour schedule:
1. Try to adhere to a routine each day.
2. Spend time outdoors when it’s light outside to boost your wakefulness.
3. Get enough daily exercise — 20 or more minutes of aerobic exercise is generally recommended.
4. Sleep in an environment that promotes rest with proper lighting, a comfortable temperature, and a supportive mattress.
5. Avoid alcohol, caffeine, and nicotine in the evenings.
6. Power down your screens well before bedtime and try engaging in an activity such as reading a book or meditating.
7. Don’t nap late in the afternoon or evening.
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