How Morning Sunlight Can Change Your Sleep

Circadian Rhythms Are Strongly Influenced by Light Exposure

Woman watching sunrise
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When is the last time you got sunlight exposure immediately upon awakening? Was it on a camping trip long ago? If you are like most people, you have likely lost an intimate connection to our planet’s most important influence. How does sunlight affect our timing of sleep and support wakefulness? Learn about this natural relationship and how it might impact unexpected aspects of our health, including circadian rhythm sleep disorders and even metabolism.

A Trip Back in Time

To understand how important morning light is in our lives, let’s imagine life 40,000 years ago as a neanderthal. If you were lucky, perhaps you lived in a cave dwelling, but it is likely you were even more exposed. When the sun set, it was time to bed down and go to sleep. If you didn’t, there was a real possibility that your safety and health were at risk – either due to exposure to the elements or from predators. Spending 8 hours in a state of unconsciousness is not the ideal way to defend yourself. You might sleep alongside others for added protection.

When the sun came up, it would be time to rouse and resume the search (or work) for food. With light, it was no longer safe to lie unconscious. Morning sunlight evolved as an intense signal to the brain that promotes wakefulness. Its profound influence on the timing of sleep and wakefulness is linked to its influence on the body’s circadian rhythm.

Light’s Impact on the Body

All light enters the eye and via the retina travels along the optic nerve to the brain. Each optic nerve crosses at the optic chiasm and just above this is the hypothalamus. The hypothalamus is like a control system for the body, influencing the circadian (Latin for “near day”) timing of sleep and wakefulness, hormone release, and metabolism.

The suprachiasmatic nucleus within the hypothalamus takes the information from light and translates it into influences on the body’s processes.

Sleep is dependent on both the sleep drive and circadian rhythm. Although the circadian rhythm will persist without external influence, consistent with its genetic basis, sunlight powerfully controls it. In particular, morning sunlight can initiate the circadian alerting signal during the day and impacts the timing of sleep at night. Therefore, getting sunlight upon awakening can improve daytime sleepiness and ease insomnia, especially among night owls with delayed sleep phase syndrome.

How and When to Get Morning Sunlight

In order to improve your pattern of sleep and wakefulness, it is best to get morning sunlight exposure immediately upon awakening. Sunlight is best as it is a broad spectrum of light and quite potent, with 100,000 lux of intensity. For comparison, room lights may be 1,000 lux and an expensive light box may be 10,000 lux. It is necessary to wait for sunrise, and if you live at northern latitudes in the winter, it may be hard to get light exposure into your morning routine.

Therefore, a light box may be necessary.

Try to go outside upon awakening (of after sunrise) and get direct light into your eyes. It is unnecessary (and unsafe) to stare directly into the sun. Instead, avert your gaze and let the sun wash over your face. Don’t wear sunglasses or hats with bills or visors. If concerned, apply sunscreen, though the sun’s morning light is less intense. Spend 15 to 30 minutes in the sunlight. It is the perfect time to go for a walk, eat breakfast, have a cup of coffee, read the newspaper, or admire your garden.

Sunlight filtered through a layer of clouds or obtained from inside through windows is less intense. It may still help some, and if this is your only option, it may be good enough. Don’t let weather determine if you are going outside. Try to go out every day to keep the habit, no matter the weather. As needed, dress warmly or bring an umbrella. Even when filtered through clouds or rain, the sunlight will continue to have its effect.

Our bodies respond best to a regular sleep schedule with a consistent bedtime and wake time. You may be surprised how getting just 15 minutes of sunlight upon awakening can help you to sleep and feel better. If you struggle with getting to sleep or feeling alert during the day, speak with a sleep specialist about other ways you might improve your rest.

Source:

Kryger, MH et al. "Principles and Practice of Sleep Medicine." Elsevier, 5th edition.

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