Michael Jain writer

June 11, 2009

A recent study tells us that we have genes in our bodies that are activated every 8 hours. What does this tell us about our internal body clocks?

Everyone agrees that as humans we are shaped by both our genetics and by our environment. A great example is that we have circadian rhythms, or internal body clocks. These circadian rhythms control many aspects of our behaviour, such as the fact that we try to be awake during the day and asleep during the night.

Did You Know?
Like humans, some animals are diurnal (awake during the day), while other animals, such as mice, are nocturnal (much more active at night). Some animals, such as certain bats, are diurnal during some months and nocturnal during others. All of these behaviours are controlled by a circadian rhythm generator found in the hypothalamus of the brain.

Circadian rhythms are thought to be ancient biological processes, as they are found even in fungi and plants. Some fungi only replicate their DNA at night so that they can avoid the harmful effects of UV sunlight on their DNA. Humans and most animals can replicate their DNA any time they want because of their protective layer of pigmented skin.Nonetheless, circadian rhythms have evolved to be important in a wide variety of human and animal activities.

Did You Know?
Our circadian rhythms are hard-wired into our bodies. Circadian rhythms are found inside the cells of our brain, liver, lungs, and every organ in our bodies. Thus, scientists believe that a great deal of our bodily functioning is affected by our sleep/wake cycle. That said, sunlight can modify or reset some of our circadian rhythms through a direct pathway from the eye to the hypothalamus of the brain. This feature is what allows us to recover from jet lag when we take a long trip!

What happens when we try to go against our circadian rhythms, staying up all night and sleeping all day? Some evidence exists that poor sleeping patterns have an overall negative effect on our health. Interestingly,mutant mice which do not have any circadian rhythms are often in poor health, with obesity, diabetes and other metabolic problems.

Did You Know?
Some medicines (such as some types of chemotherapy for cancer) can have very different effects depending on the time of day they are administered!This difference does not have to do with how our body digests and metabolizes the drug, but on the actual function of the drug on the body. This is due to the interaction of the drug with our circadian rhythms.

Most genes involved in circadian rhythms are activated every 24 hours, which corresponds to once per day. A recent study has now found genes that are activated every 12 hours or every 8 hours. These genes were found not in the brain, but in the liver and five other tissues. Why might the liver want to have a program that gets activated every 8 hours?It's not clear, but one clue was that when mice were prevented from getting food during the night (when they are usually active) and instead fed during the day, these circadian rhythms went away. One interpretation of this data is that these cycling genes are important in food and energy metabolism, as the liver is an important organ for converting digested food into various types of stored energy.Apparently, our bodies love a schedule. So get your beauty sleep!

Learn More!

Study showing that we have genes which activate every 8 hours:

http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1000442

E! Science News commentary on the above article:

http://esciencenews.com/articles/2009/04/23/a.biological.basis.8.hour.workday

Wikipedia article on circadian rhythms:

http://en.wikipedia.org/wiki/Circadian_rhythm

Renowned circadian rhythm researcher Dr. Joseph Takahashi's web page:

http://www.hhmi.org/research/investigators/takahashi.html

Michael Jain is a freshly graduated M.D.-Ph.D. from McGill University in Montreal, Quebec. He is starting a medical residency at the University of Toronto, where he will test the effect of sleep deprivation on his own physiology!

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