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Posted at 10:30 AM ET, 08/05/2009

Sleeping Through Sunlight: Not a Success

Wx and the City

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"This is getting ridiculous," I think, cursing the solstice as I awake around 5:30 a.m. when the first hues of orange and pink sunlight strike my bedroom walls on a late-June morning.

It's not that I don't appreciate the sun and all the benefits it brings, including fueling Earth's weather. But, despite putting up mini-blinds and dark curtains on my east-facing bedroom windows and covering my head with a pillow, the first persistent sun ray of the day -- all 120 watts per square meter of it -- seems to burst its way through a glitch in the system, straight to my eyes. I sigh as I roll over and shut off the alarm clock hours before it is supposed to sound ... there's no point in attempting to fall back asleep now.

Formerly a chronic night-owl, I've been defending myself against the sunrise since last year, when I moved into a place with more sunlight. (Before that, I had inhabited a light-deficient abode.) Since then, my houseplants and I have enjoyed a bright apartment, but my sleep-wake cycle has been off. I'm guessing I'm not the first person to have her sleep affected by the amount of sunlight she receives.

Come to find out, sunlight has a lot to do with regulating the human body, including stopping production of the hormone melatonin that induces sleep.

Keep reading for more on sunshine and the sleep-wake cycle...

As you've probably noticed, humans are diurnal animals: we sleep during the night and are active during the day, as opposed to nocturnal creatures that are active at night (e.g., an opossum) or crepuscular creatures that are active at dawn or dusk (e.g., a firefly). Without exposure to sunlight, our bodies would operate on a 25-hour daily cycle. However, add sunlight to the picture, and it becomes a 24-hour cycle: a day and night on Earth.

When sunlight enters our eyes, it triggers photoreceptors (light-detecting cells) in the retina. These alert the body's "biological clock" (a small area in the brain), which sends signals to other areas of the brain, telling the body it's time to wake up: production of melatonin is halted by the pineal gland; body temperature rises; urine production and blood pressure increase; etc.

Lifestyle can affect how much sunlight and darkness we're exposed to, and thus affect our sleep. People who travel across time zones often experience jet lag symptoms, including disruptions to their normal sleep-wake cycle. Their bodies can adjust to a new schedule of sunlight, though it may take a few days. Those who work night shifts can have a more difficult time adjusting, since they are not exposed to enough sunlight and do not sleep during the night, when their melatonin production is highest (check out this diagram). Even those of us who work in office buildings can experience effects on our sleep-wake cycles from lack of sunlight during the day.

Weather and climate can affect the sleep-wake cycle, too. For example, sufferers of Seasonal Affective Disorder, a disease that can affect people who live in northern latitudes with long, dark winters, sometimes have to go through phototherapy (exposure to powerful artificial light) to reduce their symptoms.

For people who have trouble falling asleep, a helpful and surprising tip is to get outdoors for a half-hour to hour of early-morning sunlight (before 8:30 a.m.) each day. This helps the body's clock get back on schedule. For people who wake up too early, increasing your exposure to evening sunlight may help.

I've experienced a long and sometimes challenging adjustment this past year. The good news is that, given a chance, the human body can adapt to a more biologically appropriate sleeping schedule, and I've learned to listen to it. After years of resisting the thousands of years of evolution that have perfected the human biological clock, who would have thought that I'd start waking up with the sun?

Have you experienced a shift in your sleeping patterns based on sunshine or other types of weather? Let us know in the comments section below.

Current sunrise and sunset times for Washington, D.C.
Sleep and Circadian Rhythms
Brain Basics: Understanding Sleep
Jet Lag and Shift Work
Lifestyle Practices that Can Improve Sleep
How to Fall Asleep
Diurnal and age variations in human melatonin levels (from this study)

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