Good sleep starts in the morning. I love this paradox.
Our circadian rhythm dictates our cycle of sleeping and waking. In the morning, cortisol rises and melatonin is low or ‘suppressed’. Over the day, as the body prepares itself for sleep, cortisol drops and melatonin rises. See below.
The following factors influence the circadian rhythm:
- The intensity, spectra and timing of light both natural (i.e. the sun) and artificial (i.e. screens, indoor lighting).
- Food intake, in particular carbohydrates, and its timing.
- Fluid status and temperature
- Caffeine intake
- Stress levels
- The intensity and timing of exercise.
- The regularity of sleep and wake times.
The number 1 factor is light. Light has more effect on your sleep than your high school crush had on your grades. Light intensity (i.e. lux), the light spectrum (i.e. wavelength) and the timing and duration of light all matter.
Light intensity and timing
We measure light in lux. One lux is the amount of light emitted from a candle over a 1 metre radius. All sources of light are not created equal. See below.
Bright sunlight at noon: 100,000 lux 1
Cloudy day: 25,000 lux 1
Overcast day: 2-10,000 lux 1
Bright industrial lighting: 1-5,000 lux 1
Offices and kitchens: 200-500 lux 1
Household lighting: 50-200 lux 1
Street lighting: 20 lux 1
Full moon: 1 lux 1
Computer screen: 0.5-37.8 lux 2
Tablets: 0.7 to 5.9 lux 2
TVs: 0.03 to 0.5 lux 2
Smartphones: 0.6 to 2.1 lux 2
The brighter the light, the more likely it is to drive a cortisol spike and suppress melatonin. We therefore want brighter light during the day, particularly in the morning, and then dimmer light towards the end of the day. This will increase alertness and decrease sleepiness during the day. Natural sun light, even if it’s overcast, trumps any other form of artificial light. Now overlay this with the reality that we spend most of the day indoors. Again, good sleep starts in the morning with natural sun light.
Light spectrum and timing
The visible light spectrum ranges from violet light (400nm) to red light (700nm). Blue light is 420-480nm. Blue light can come from sunlight, screens (e.g. smartphones, laptops, tablets, TVs) as well as fluorescent and LED lights. Even at a low intensity for short durations, blue light suppresses melatonin and decreases sleepiness. This is great in the morning and a disaster at night.
Lifestyle prescription: 15 minutes of morning sunlight exposure. Don’t wear sun glasses so the back of your eyes can soak up all the glorious lux.
Useful hacks: Eat breakfast outside, go for a morning walk, meditate outside.
In the next article, I will explore light at night. If you know someone who will find this useful, please share this newsletter with them.
Much love to you and of course, to myself.
- Foundations of lifestyle medicine board review manual (3rd edition)