Day 72 of Coronavirus Lockdown and for the first time in a long time, it’s raining, so my morning walk wasn’t quite as enticing as it has been. But it was still thoroughly enjoyable. I mentioned in my previous post that I have set myself the challenge to walk 50,000 steps per week. I know that 10,000 steps per day is a desirable goal, and I know I could, (and should), have achieved it whilst being furloughed. Walking 10,000 steps per day equates to approximately five miles and, when walking at a moderate pace, takes 1-1.5 hours. When I go back to work, I don’t think I’ll have the time to do this, so I have chosen a target that’s both attainable and sustainable. It should add up to at least 150 minutes of exercise per week, the recommended weekly amount.
I have always preferred to exercise first thing, before breakfast. Part of this is simply because it gets it done. I find it gives me a better mindset for the rest of the day- if I have a healthy start, I’m more likely to eat healthily for the rest of the day. It wakes me up too, although I’m naturally inclined to be more lark than owl. These anecdotal reasons are good enough for me. But a lot of science supports why walking in the morning is good for you.
Circadian Rhythms And The Visual System
Humans and most living things have a circadian rhythm which affects sleep patterns, hormones, body temperature and eating habits. The control centre for this is in the hypothalamus of the brain. Genes and other natural factors govern these rhythms in the main. (My parents are larks like I am). But external factors also play a part and the most important one is light. Human beings are hard-wired to sleep when it’s dark and wake when it’s light. The visual system is linked directly to the hypothalamus.¹´² When daylight fades, the eyes send a signal to the brain to make melatonin, the sleep hormone. When the sun rises, those signals tell the brain to reduce the melatonin.
Blue Light and The Eyes
So, blue wavelengths of light are absolutely essential to help to regulate the circadian rhythm, but what about blue light from phones, tablets and other devices? There is absolutely no evidence to show that it damages the eye in any way. Blue light is part of the visible spectrum and therefore is harmless to the human eye. But, it CAN upset the circadian rhythm. As I said above, humans take evening light as a cue to the brain to increase the production of melatonin.
If we stare at devices at 11pm, (guilty as charged), the blue light they emit can trick the brain into thinking it’s morning. This is why the night-shift mode on a device alters the screen to look less blue and more yellow. It mimics, to some extent at least, the wavelength of natural evening light.
The Benefits Of Sunlight Versus Protecting The Eyes
The benefits of sunlight are well-known. Most of the health-promoting benefits of sun exposure are thought to occur through vitamin D photosynthesis³. But, we also know that too much exposure is harmful to eyes and skin alike. (I wrote an article last year about UV damage to the eyes and how to protect them). UV rays are present whatever the weather and it’s important to use UV protection. However sunglasses, glasses and contact lenses block out some of the harmless wavelengths from the visible spectrum too, the very same that we need to regulate the circadian rhythm. Therefore, I do my morning walk without sunglasses or glasses and wear them at every other time. That way, I get the benefits of the natural light when I need it most. And of course, another reason to walk in the morning is that the UV index is lower than later in the day.
- Vision and the Hypothalamus
- The Circadian Visual System
- Benefits of Sunlight: A Bright Spot For Human Health