The Importance of Dark at Night

Dark at nightI’d like to share with you a fantastic episode of The Nature of Things called Lights Out! that succinctly and powerfully demonstrates the effect on our health from exposure to light at night.

Your body clock

We all have a “body clock”, or circadian rhythm and light is a major signal that keeps us “on time.” A part of the brain called the superchiasmatic nucleus prompts the pineal gland to produce melatonin when we are exposed to darkness. This hormone, melatonin, affects many other systems of the body during darkness when we sleep. Then, when we are exposed to light again in the morning, melatonin drops and our daytime functions begin.

This daily rhythm is very important and has a major impact on health and disease. It is only relatively recently (the last 130 years) that human beings have disrupted this rhythm via being indoors during the day and had so much exposure to light at night.

We’ve long known that shift workers face many more health risks just by virtue of the disruption to circadian rhythm caused by working at night and conversely, the Amish, who don’t use electricity, have much lower levels of obesity (despite a high caloric intake and high saturated fat intake), heart disease, metabolic syndrome, and depression. Aren’t we lucky to have such diverse populations to study for such information?

I’ve highlighted several areas this program explored with regards to how exposure to light at night affects health:

Cancer risk:

  • Breast cancer incidence and mortality is highest in industrialized countries where exposure to light at night is highest.
  • Human breast cancer cells implanted into mice exposed to light round the clock grew into measurable tumours quickly, while tumours did not appear in control mice who had 12 hours of darkness.
  • Tumours in mice perfused with human blood samples taken from women exposed to light were much more active and grew faster than tumours perfused with blood samples from women exposed to dark.
  • 20 years of night shift work was associated with a 79% increase in risk of breast cancer! Wow.
  • Shift work that disrupts circadian rhythm is likely carcinogenic (cancer-causing) in human beings! Shift work is in the same risk category as anabolic steroids, UV light exposure, and diesel engine exhaust.

Weight and metabolism:

  • Mice exposed to light at night gained 20% more (!) body mass than controls with the same caloric intake.
  • Eating later at night leads to weight gain via disrupted metabolism – so that rule of thumb to eat lighter at night and stop eating several hours before bed is really good advice!

Heart health:

  • Mice kept in the dark at night had a survival rate after heart attack of nearly 100% while in mice exposed to just 3 nights of dim light (such as we humans may be exposed to in a hospital setting overnight with all the monitors and machines!), survival rates dropped to just 30-40%.


  • Mice exposed to chronic low levels of light at night exhibited a loss of interest in things they normally had enjoyed (one major sign of depression).
  • On a positive note, these effects are highly reversible in a short period of time when darkness at night is restored, so there is hope for you if you’re feeling down – turn out the lights!

What can I do?

1. Become Amish

Is it possible to convert to or join the Amish? Or, you could stop using electricity, eat only foods you grow and prepare, and engage in lots of character-building physical labour. If this doesn’t interest you, keep reading.

2. Prioritize your circadian rhythm

  • Accept your status as a human being – to function well you need both light and dark exposure and a minimal amount of sleep and it is your responsibility to ensure you get what you need.
  • Most research shows that health is optimal when people get at least 7-8 hours quality sleep per night consistently, so plan your day and night to give yourself this important rest.

3. Eliminate sources of light while you sleep.

If you open your eyes at night, you shouldn’t be able to see ANYTHING!

  • Black out your windows with opaque blinds or curtains.
  • Get rid of night lights already! And cover sources of light, such as clocks and electronics.
  • Wear a sleep mask to cover your eyes and block out light.

4. Use colour appropriately

And I don’t mean what you’re wearing!  Red light suppresses melatonin production the least, green light is in between, and blue light suppresses melatonin the most. This patten happens to mirror the colour of light from the sun at different times of the day (ingenius!).

  • Eliminate sources of blue light in the evening, such as TVs, computers, and other electronics that can suppress melatonin production for up to 90 minutes! So yes, the advice to avoid electronics at night is also true!
  • Keep lights dim and warm in the evening using different lamps or dimmers.
  • Emphasize red light at night, such as using candlelight or fire. Also good for romance!
  • If you wake during the night, avoid bright lights (including those cursed electronics) and if you must have light, stick to dim red-toned light.

5. Ensure that your days are light

  • Get outside in the light for at least 20 minutes per day.
  • Use more blue light during the day, such as the light from compact fluorescent light bulbs.

6. If you are a shift worker, take steps to protect your health

  • Seriously consider if shift work is right for you, and if not, start taking steps to change your work schedule.
  • Plan a sleep schedule that ensures you get consistent undisturbed sleep when you are not working.
  • Sleep in complete darkness and observe other tips for sound sleep.
  • There appears to be some benefits to increasing light (ideally blue) while working and shifting to less light (and warmer colours, like red) once finished work to simulate nighttime.
  • However, there is also research which aims to prevent the changing of the circadian rhythm in shift workers by reducing exposure to blue light which also shows benefit.

7. See your naturopathic doctor

To address any issues falling asleep, staying asleep, or getting restorative sleep. There are many wonderful treatments to improve sleep that are gentle and safe. You deserve to sleep well and wake up feeling great!

Want to learn more?

I highly recommend the book Lights Out: Sleep, Sugar, and Survival by T.S. Wiley for more information about how light and dark signals affect our health. You can also check out a previously blog I wrote about the connection between sleep and weight.


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