Wednesday, April 22, 2009

What’s Your Chronotype? Understanding the “Lark” and “Owl” Circadian Sleep Patterns

A New York Times column examines the factors that contribute to your preferred sleep schedule.

This is also called your “chronotype.” It turns out that your DNA has a strong influence on when you like to sleep.

Some people have a circadian clock that makes them “evening types.” These “owls” have a natural tendency to stay up late at night and sleep late in the morning. Children tend to become night owls
as teens because of a shift in the timing of their circadian clocks.

Some night owls have
delayed sleep phase disorder. This involves a struggle to conform to work or social demands. It can be difficult for them to function well during the day.

Other people are natural “morning types.” These “larks” prefer to go to bed early and wake up early. Adults often become larks
as they get older.

Some larks have
advanced sleep phase disorder. They fall asleep several hours before a normal bedtime. As a result, they also wake up hours earlier than most people wake in the morning.

So do larks have an advantage over owls? After all, it was Benjamin Franklin
who said, “Early to bed and early to rise, makes a man healthy, wealthy, and wise.”

A study in 1998 put these words to the test. It found no evidence that larks were healthier, wealthier or wiser than owls.

Not everyone fits neatly into the categories of morning or evening types. Many people are somewhere in between the larks and the owls.

And many factors such as genetics and light exposure affect when you are sleepy and alert. A
new study in the journal Sleep examined some other factors.

It involved 5,720 college students at two universities in Spain and Italy. Results show that females went to bed earlier and slept longer than males.

Nationality also had a significant effect on sleep patterns. On average the Spaniards went to bed and woke up later than the Italians.


The study even found a significant but small “season of birth” effect. Subjects born in spring and summer went to bed later than those who were born in fall and winter. A study in 1999 reported similar findings.

Image by Rachel

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