Our body is designed to have a rhythm. Several rhythms, in fact. Some rhythms are seasonal, some relate to the moon (monthly), others coincide with the light and dark cycle of day and night. Let’s look today at what effects changes in light and dark cycle (our circadian rhythm) have on our body. Is messing with this natural cycle affecting our health?

Our physiology is organized to change with time. The daily changes that happen are very important for our health and wellness. For example, we need rest and sleep in order to heal and restore.  

Light and absence of light, detected by the eye, is the major cue used by the body to discriminate day from night and to create our circadian rhythm. If this rhythm is disrupted, many parts of our physiology can be affected. 

Take a look at the infographic below which shows some of the physiological factors that vary from the light of day to the dark of night.

Infographic showing the changes in physiology between day and night from CALMERme.com

From the above, we can see that many different systems in our bodies have a rhythm. This temporal organization of our physiology is critical for our health.

Disruption of our circadian rhythm has been linked to many disease processes, including metabolic syndrome, obesity, cardiovascular diseases, neurodegenerative disease, intestinal dysbiosis, inflammatory bowel disease, and cancer. 

In the past, we had predictable periods of daily light and dark, driven by the sun rising and setting. These set our circadian rhythms. When it was daylight, the physiology on the left-hand side of the infographic applied and when it was dark, that on the right-hand side applied.

The electric light bulb

But then the electric light bulb was invented.  This has significantly impacted our light and dark cycle, drastically reducing the dark part.  The part when our body is healing. 

Our boundaries of light and dark are now blurred. The sun goes down and we turn on the lights. Instead of natural light-dark cycles, we now use lights to illuminate us for 4 or more extra hours. Our biological processes are consequently not as synchronized as they used to be. This means hormones, gene expression, immune function, mood, metabolism, our gut microbiota may all be affected. 

Light:dark time importance

Light and dark are the key. It’s not just asleep and awake. It is those triggers that shift us from one stage to the other and having a rhythm that the body can be entrained towards.  Our nighttime physiology is our dark physiology not just sleep physiology. The dark transitions us. Things begin to change as the light disappears. 

Time to go back to the light of fires and candles? 

Obviously, we don’t want to give up the convenience of our electric lights and stop using light emitting electronic devices like televisions, computers, iPhones etc at night. None of this huddling around the fire or candles to read our paper. But if this light is affecting our health is there something we can do? I’ll explore some options next week. 

In the meantime, pay attention to how many hours you use lights in the house after it is dark outside. How bright are your lights at home? How close to bedtime do you watch TV or use computer/phone screens? If you get up in the night to go to the bathroom, do you switch the light on?

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Sleep tight.

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