What is the body clock?
The body's "biological clock," or 24-hour cycle (circadian rhythm), can be affected by light or darkness, which can make the body think it is time to sleep or wake up. The 24-hour body clock controls functions such as:
- Sleeping and waking.
- Body temperature.
- The body's immune system.
- Other body functions, such as when you feel hungry.
How are body clock problems and sleep problems connected?
Body clock sleep problems have been linked to a hormone called melatonin, which helps your body fall and stay asleep. Light and dark affect how the body makes melatonin. Most melatonin is made at night. During the day, light tells your body to make less melatonin. If you work at night in artificial light, your body may be making less melatonin than it needs.
Some people—such as those who can't sleep until very late and those who go to bed very early—have circadian (say "ser-KAY-dee-un") rhythms that are different from those of most people. Other people with sleep problems may have regular circadian rhythms but have to adjust them to new situations, such as working a night shift.
What sleep problems are related to problems with your body clock?
Things that may affect melatonin production and can cause sleep problems include:
- Jet lag. Crossing time zones disrupts your body clock. You have sleep problems because your body clock has not adjusted to the new time zone. Your body thinks that you're still in your old time zone. For example, if you fly from Chicago to Rome, you cross seven time zones. This means that Rome is 7 hours ahead of Chicago. When you land in Rome at 6:00 in the morning, your body thinks it's still in Chicago at 11:00 the previous night. Your body wants to sleep, but in Rome the day is just starting.
- Changing your sleep schedule. When you work at night and sleep during the day, your body's internal clock needs to reset to let you sleep during the day. Sometimes that's hard to do. People who work the night shift or rotate shifts may have trouble sleeping during the day and may feel tired at night when they need to be alert for work.
- Your sleep environment. Too much light or noise can make your body feel like it is not time to sleep.
- Illness. Certain illnesses and health problems can affect sleep patterns. These include dementia, a head injury, recovering from a coma, and severe depression. Some medicines that affect the central nervous system may also affect sleep patterns.
- Aftereffects of drugs and alcohol. Some drugs cause sleep problems. And you may fall asleep with no problems after drinking alcohol late in the evening, but drinking alcohol before bed can wake you up later in the night.
Other sleep problems related to the body clock include:
- Having a hard time falling asleep until very late at night or very early in the morning and then feeling tired and needing to sleep during the day. People who have this problem may be called "night owls." This is a common problem, and it usually starts in the early teen or young adult years. People who have a parent with this problem are more likely to have it themselves.
- Falling asleep early—at 8 p.m. or earlier—and waking up early—between 3 a.m. and 5 a.m. If you wake up early, you may be called an "early bird." This problem is not as common as staying up late and waking up late. Experts are not sure what causes it.
How can you treat sleep problems related to your body clock?
How you treat a sleep problem related to your body clock depends on what is causing the problem. Here are some tips for the most common problems.
Taking melatonin supplements may help reset your body clock.
Suggestions about times and dosages vary among researchers who have studied melatonin. Doctors recommend that you:
- Take melatonin after dark on the day you travel and after dark for a few days after you arrive at your destination.
- Take melatonin in the evening for a few days before you fly if you will be flying east.
The safety and effectiveness of melatonin have not been thoroughly tested. Taking large doses of it may disrupt your sleep and make you very tired during the day. If you have epilepsy or are taking warfarin (such as Coumadin), talk to your doctor before you use melatonin.
The sleeping pills eszopiclone (Lunesta) and zolpidem (Ambien) have been studied for jet lag. They may help you sleep despite jet lag if you take them before bedtime after you arrive at your destination. Side effects include headaches, dizziness, confusion, and feeling sick to your stomach.
For more information on jet lag, see:
If you work the night shift or rotate shifts, you can help yourself get good sleep by keeping your bedroom dark and quiet and by taking good care of yourself overall. In some cases, prescription medicine or over-the-counter supplements may help. Here are some tips on sleeping well when you do this type of shift work:
- Make sure that the room where you sleep is dark. Use blackout drapes, or wear a sleep eye mask.
- Wear earplugs to block sounds.
- Don't have alcohol or caffeine in the hours leading up to bedtime.
- Take a nap during a work break if you can.
- Ask your doctor if you should try a dietary supplement or medicine. Doctors usually advise people to use a supplement or medicine only for a short time.
For more information, see the topic Shift Work Sleep Disorder.
Some people, no matter what they do, have trouble falling asleep at night and being up early during the day. This may or may not cause problems for them. It depends on their lifestyle and work or school schedule. If you are one of those night owls, there are things you can try so that you fall asleep earlier and sleep through the night.
- Getting up at the same time every day no matter what time you go to sleep. On the weekends (or on days when you don't have to get up), don't let yourself sleep more than 1 hour longer than you do when you have to get up for work or school. If that doesn't work, you can try the treatments listed below.
- Light therapy. In this case, light therapy means exposing yourself to bright light as soon as you wake up. You can use sunlight, a bright (10,000 lux) light, or a full-spectrum light box for 30 to 45 minutes each day.
- Melatonin . Ask your doctor about taking melatonin supplements in the evening to help you get to sleep.
- Chronotherapy. For night owls, this method involves creating a 27-hour day. During each sleep-wake cycle, you go to sleep 3 hours later until the time to go to sleep has cycled back around to the time you actually want to go to sleep. After you complete the cycle once, then you would keep going to bed at that desired time. This method can be hard to do because of the way it can disrupt your daily schedule and because you have to keep to a rigid schedule. Here is a sample schedule:
- Day 1: If you normally go to bed at midnight, you would wait until 3 a.m. to go to sleep.
- Day 2 and beyond: Go to sleep at 6 a.m., and then keep delaying sleep 3 hours each day until you are going to bed at the time you desire. This will probably take 5 to 7 days.
People who fall asleep very early and wake up before dawn may try the following to try to stay up later at night and sleep later in the morning.
- Light therapy. In this case, light therapy means exposing yourself to bright light in the evening. Use a bright (10,000 lux) light box for 30 to 45 minutes each day.
- Chronotherapy. For early birds, this method involves creating a 21-hour day. During each sleep-wake cycle, you go to bed 3 hours earlier until the time to go to sleep has cycled back around to the time you actually want to go to sleep. This method can be hard to do because of the way it can disrupt your daily schedule and because you have to keep to a rigid schedule. Here is a sample schedule:
- Day 1: If you normally go to bed at 8 p.m., you would go to bed at 5 p.m.
- Day 2 and beyond: Go to bed at 2 p.m., and then keep going to sleep 3 hours earlier each day until you are going to bed at the time you desire. This will probably take about a week. Then you would keep going to bed at that desired time.
After you get treatment for the illness or health problem that is causing your sleep problem, you will need to practice good sleep habits. This includes getting regular exercise, going to bed at the same time each day, and using the bed only for sleep and sex.
For more tips on improving sleep habits, see:
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Current as of: March 1, 2022
Author: Healthwise Staff
Kathleen Romito MD - Family Medicine
E. Gregory Thompson MD - Internal Medicine
Mark A. Rasmus MD - Pulmonology, Critical Care Medicine, Sleep Medicine