Sunlight and Sleep

It seems counterintuitive: Early-morning sunlight helps you sleep at night. But it’s true, because those two things are part of the sleep-wake cycle.

Light tells the brain it is time to wake up. That's probably obvious to anyone who has had to turn on a light in the middle of the night and then has had trouble getting back to sleep. What may not be so obvious is that exposure to light at other times, particularly in the early morning, can actually help you sleep at night.

How does morning light improve sleep? The light helps to regulate your biological clock and keep it on track. This internal clock is located in the brain and keeps time not all that much differently from your wristwatch. There does, however, appear to be a kind of forward drift built into the brain. By staying up later and, more importantly, getting up later, you enforce that drift, which means you may find you have trouble getting to sleep and waking up when you need to.

To counter this forward drift, you need to reset your clock each day, so that it stays compatible with the earth's 24-hour daily rhythm -- and with your daily schedule. Exposing yourself to light in the morning appears to accomplish this resetting.

Research has shown that people who are deprived of light for long periods of time (and so do not have their biological clocks reset) experience dramatic changes in their sleep, temperature and hormone cycles. Although you probably won't be deprived of light for an extended period, getting less morning light than you need may make it more difficult for you to fall asleep and wake up at your preferred times.

Many factors can affect our biological clock, but light appears to be the most important. The timing of exposure is crucial; the body clock is most responsive to sunlight in the early morning, between 6 and 8:30 a.m. Exposure to sunlight later does not provide the same benefit. The type of light also matters, as does the length of exposure. Direct sunlight outdoors for at least one-half hour produces the most benefit. The indoor lighting in a typical home or office has little effect.

Specially designed light boxes and visors that simulate sunlight are available. (They are often prescribed to treat seasonal affective disorder, or SAD, a form of depression that tends to occur seasonally, during the darker winter months.) Still, a half hour in front of even the most powerful light box does not provide as much phototherapy as does a half hour outside on even an overcast day.

You can’t control when the sun shines, but you can control the level of stress in your life. Find out on the next page how stress affects sleep.

For more information on how to get a good night's sleep, see:

• How Sleep Works
• How Sleep Problems Work
• Causes of Insomnia
• Sleep Medications
• Natural Sleep Aids
• How to Help A Child Who Is Having Trouble Falling Asleep
• Is Lack of Sleep Making Me Fat?
• Is Science Phasing Out Sleep?