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What happens when you mess with your body's internal clock

By: Julia Segal, Queen's University

George Harrison inadvertently highlighted the importance of light when he wrote ‘Here comes the sun’ in 1969. Since the beginning of humanity, sunlight has driven our physiology, behaviour, and genetics.

The human body follows an internal 24-hour clock called a circadian rhythm. These rhythms become synchronized by light, which can include natural sources such as the Sun or artificial light sources such as the lighting in your home. Once detected by our eyes, the presence or absence of light is transformed into a signal that gets sent to a special region in the brain that controls our circadian rhythms. It’s thanks to these rhythms that your body knows when to wake up in the morning, when the optimal time to digest is, and when our immune systems can take a breather. Almost our entire body is synchronized to this rhythm. This allows us to conserve resources during times when we don’t need them (e.g. during sleep) and maximize them when we do (e.g. doing normal daily activities).

But what happens when our internal clock becomes out of sync? This can happen when you travel across time zones (jetlag), or for those who work night shifts. Doing this once or twice is not a big deal, but people who do this frequently or for many years risk negative health effects. For example, chronic night shift work can increase your risk for health problems, such as multiple sclerosis and cancer. Of course, not everyone travels or works nights, but there is one other phenomenon that messes with circadian rhythm that probably does affect you.

Every year in March and November, millions of people across North America change their clocks in synchrony. The idea of waking up earlier to take advantage of the sun was first jokingly proposed by Benjamin Franklin, who wanted to wake Parisians earlier in the winter by shooting noisy cannons in order to conserve candle usage. Daylight savings was eventually implemented in 1917, and has subsequently exhausted almost an entire continent for a hundred years.

So what, you might ask? Two days a year of sleep deprivation never killed anyone, right?

Wrong. This one-hour shift in our schedule actually correlates with an increase in the number of car accidents the following day. Even more alarmingly, however, is the fact that this clock shift increases the risk of heart attacks. The exact statistics vary between different studies, but it’s estimated that the risk of heart attack increases by 4 to 29% during the days following the spring time change.

On the other hand, some people are better at waking up early than others. Another aspect of circadian rhythms you might be familiar with is the idea that some people are early birds and others are night owls. The technical term for this is chronotype, and refers to an individual’s sleep preferences. Someone who is a “morning type” wakes up naturally early, and has their most productive hours in the morning. In contrast, “evening types” prefer to sleep in later and are most focused at night. Generally, evening people are the unlucky ones who end up sleep deprived when they stay up late but are then obligated to wake up early for school or work, and may even be more at risk for some health conditions.

The good news is that while circadian rhythms make daylight saving time and, for some, waking up early inconvenient, we can also use circadian rhythms to our advantage. Strategies can be used to improve treatment efficacy by administering medication at specific times of day. One way to do this is to take the medication at the time of peak symptom intensity. Many conditions have symptoms that follow a circadian rhythm; for example, arthritis pain is known to peak in the morning, while diabetes-related nerve pain peaks in the evening. A popular example of this is glucocorticoid treatments, which is more effective at reducing both multiple sclerosis and rheumatoid arthritis symptoms when taken at night.

There’s a lot we can learn from circadian rhythms about our day to day lives – like the best way to time your sleep to enhance your daily performance – but their role in health and disease is proving to be very important too. Research will continue to explore this topic, and hopefully lead to better treatment and management of various health conditions.

Edited by B.G. Borowiec and A.E. McDonald. Header photo from Unsplash.

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