Circadian rhythms

To better understand why light can have such an affect on us, we need to think about our circadian rhythms. Your circadian rhythm (often called sleep/wake cycle) is like an internal clock that cycles between sleepiness and alertness throughout the day depending on which hormones are being released. It’s profoundly affected by light, as well as how bright the light is and, possibly, what colour it is too.

As the sun goes down, melatonin (a suppressant hormone) is released. This encourages you to sleep, so when it’s dark you feel more tired. Conversely, as the sun rises, melatonin secretion stops and serotonin is released, waking you up. Being outside and in the day light is the best way to waken up for this reason. If we keep the curtains drawn, it delays this hormonal change.”

A combination of light and colour might be the answer to better sleep. Caroline McCrystal explained: “In recent years we’ve been exposed to what we call ‘blue light’. This travels into the retinas, even with your eyes closed, and prevents melatonin being produced properly. The pineal glands will keep producing serotonin, which will keep you alert.”

Although this thinking is backed up by research, like this 2012 study about red light, sleep and performance, often scientific trials are carried out with very powerful lights that we can’t replicate in our homes – not yet at least. This doesn’t mean we shouldn’t reap the rewards of soft, warm light in the evening and bright light in the morning if it helps us to sleep, but it might not work for everyone.

Dr Jamie Zeitzer, assistant professor at Stanford University in the Department of Psychiatry and Behavioral Sciences and the Centre for Sleep Sciences and Medicine, who warned us to be wary of the sleepiness and wakefulness claims of modern day smart lights. “Light can directly activate wake-promoting circuits in the brain, but the light intensity to which we are exposed is probably not bright enough to have a major impact.

“There have been recent studies to indicate this kind of light exposure might more gradually wake the brain up, which could be useful in certain circumstances,” he explained. “It might also be able to activate sympathetic nervous system circuits which would allow people to awaken with more energy. But, alas, it is still an area in dire need of research.”

One 2011 study1 compared daily melatonin profiles in individuals living in room light (<200 lux) vs. dim light (<3 lux). Results showed that, compared with dim light, exposure to room light before bedtime suppressed melatonin in 99 percent of individuals, and shortened the time period when the body has an elevated melatonin level by about 90 minutes. Furthermore, exposure to room light during the usual hours of sleep suppressed melatonin by more than 50 percent. The authors concluded that

“These findings indicate that room light exerts a profound suppressive effect on melatonin levels and shortens the body’s internal representation of night duration. Hence, chronically exposing oneself to electrical lighting in the late evening disrupts melatonin signaling and could therefore potentially impact sleep, thermoregulation, blood pressure, and glucose homeostasis.”

Simply closing your eyes is not enough as light can penetrate your eyelids. Aim to make sure your bedroom is very dark. I recommend installing blackout shades for this purpose. A far less expensive alternative is to use a sleep mask to avoid disrupting your melatonin production and circadian rhythm. Also keep in mind that digital alarm clocks with blue light displays could have a detrimental effect.

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