Q.: We often hear the word "circadian rhythms" in tandem with our need for healthy sleep. What are circadian rhythms and how do they regulate when we do or don’t sleep?
Dr. Kashyap: Everything in the universe is regulated, including our individual internal rhythms. Everyone’s body has a master clock, but we tend to defy our body’s circadian rhythms when it comes to sleep. We tend to ignore our body’s need for sleep until we’ve gone so long without sleep that our body makes us rest. Trying to do more with less sleep is not healthy. Our body remembers the sleep debt we build up, and contributes to our overall well-being and performance when we are awake.
Sunlight, physical activity, and the hormone, melatonin, control our internal body clock. We know that people who do not get enough sunlight tend to be depressed. Activity prepares us for sleep. We are still learning about the body’s production of melatonin and its effect on our biological clocks. We are intended to be night-time sleepers because of our need for sunlight. When evening comes, our heart rate goes down. Our body temperature is lowest at night. We’re physically being prepared for sleep.
In the early 1970s, researchers identified the center of our biological clock, located in the upper part of the mid-brain. There are two very, very small clusters of nerve cells (the suprachiasmatic nuclei). About 10,000 of these cells have tremendous influence over our brain cells, and the trillions of cells throughout our body. These nuclei monitor light levels entering the eyes, and adjust our individual changes in body temperature, metabolic rate and hormone release.
Q: What is the normal sleep cycle?
Dr. Kashyap: Our sleep cycle adjusts with age. Before the electric light was invented, our internal clocks tied us to the rhythms of nature. Electric light gave us the ability to adjust our own sleep cycles. For the most part, adults need 7-8 hours of sleep per day. To determine one’s own sleep cycle, pick a time period with no obligations. This assumes you haven’t deprived yourself of sleep over a period of time. Go to bed and wake up when your body tells you to awaken. That’s your sleep cycle.
Sleep begins before we are born. Once a pregnancy is well along, the fetus spends about 20-24 hours asleep, and is most active during this time. By the end of the first year, an infant sleeps 14-15 hours a day, with 1-2 daytime naps. Sleep periods have shifted to night. From ages 4-12, children need 9-10 hours of sleep per day.
As we reach puberty and into the teenage and early adult years, we become "owls" – stretching the time we go to bed. The problem is getting up to meet the demands of the day. Getting 4-5 hours of sleep per day over a long period of time builds up a huge sleep debt. This is why we fall asleep in class, or nod off on the job, are sleepy behind the wheel, or why we make mistakes in our work. We still need that 8-10 hours of sleep every night.
As people age, they become "larks." They go to bed earlier and rise earlier. At this point, mature adults need about 7 ½-8 hours of sleep. Just as we can enjoy time for sleep, nature provides us less sleep and poorer quality of sleep. Daytime naps can help mature adults keep their sleep debt in check.
Q: What is sleep debt and can it be re-paid?
Dr. Kashyap: There are many examples of not having had sufficient sleep: The Exxon Valdez grounding and oil spillage was caused not by alcohol, but insufficient sleep of the third mate. He’d slept only six hours in the previous 48 hours. The Challenger disaster was attributed to a failure of the O-ring at low temperatures; but that error might have been picked up prior to launch, if the NASA managers had not had so little sleep. The Chernobyl nuclear disaster is another instance where operators had simply not had enough sleep and weren’t able to pay attention to signals of impending disaster. If you’ve ever fallen asleep, even briefly, while driving, you know the danger of sleep debt.
Every time you get less than your body’s normal need for sleep, you start adding up a sleep debt. When we awaken, our body starts the countdown of how many hours will be needed to pay off the day of wakefulness. Usually, people need to sleep one hour for every two hours they are awake. Lost sleep is like a loan that needs to be paid back. Do you ever get an overwhelming urge to take a nap? That’s your body reminding you that your sleep debt still needs to be paid.
Q: What are other examples of circadian sleep cycle disorders?
Dr. Kashyap: These include situations like jet lag and night shift work. Individuals working at night are nearly always underslept, since the person tries to stay awake during the daytime, especially on weekends. Otherwise, it would be hard to take part in social activities with friends and family. They remain somewhat sleep while working at night. And, flying over time zones creates similar difficulties. In general, flying toward the east creates more adjustment difficulties than flying west.
Q: What do you think we can do to pay attention to our body’s natural rhythms, including the need for sleep?
Dr. Kashyap: First, I think we need to teach healthy sleep, just as we teach healthy nutrition in the schools. We completely overlook one of the most important aspects of staying well.
Research has shown that individuals who are not well-slept build up a high level of C-reactive protein in their body. This is a marker for excessive inflammation, contributing to heart disease and stroke. The circadian cycle controls the clotting effect of platelet factors. Lack of sleep has been shown to influence hypertension, asthma and digestion. When you’re not well-slept, you are not as focused or productive.
The best thing you can do for yourself is to set a consistent bedtime and wake-up time that you stick with on weekdays and weekends. We’re not at all hesitant to pay attention to our body when it demands food. We need to be just as vigilant to our body and its need for sleep.