Night Owls Vs Early Birds
April 2, 2014

High Cortisol Levels May Be A Biomarker Linked To Greater Risk-Taking In Night Owls

Brett Smith for - Your Universe Online

Are you a night owl who likes to stay up to study or watch late-night talk shows? Or an early bird who likes to get a head start on the competition?

According to a new study from a University of Chicago professor, your personal sleeping habits are related to your propensity for taking risks – with night owls being higher risk takers than early birds.

The study, which was published in the journal Evolutionary Psychology, also found that sleeping preferences are linked to other personality traits.

“Night owls, both males and females, are more likely to be single or in short-term romantic relationships versus long-term relationships, when compared to early birds,” said study author, Dario Maestripieri, professor of comparative human development at UChicago. “In addition, male night owls reported twice as many sexual partners than male early birds.”

To reach his conclusion, Maestripieri used information from an earlier study of over 500 graduate students at the University of Chicago. That study examined financial risk aversion for male and female students and discovered men tended to take more financial risks than women. However, females with relatively higher testosterone levels were comparable to males with respect to financial risk-taking, the earlier study showed.

To expand on that study, the Chicago professor looked to see if sleep patterns have any effect on these risk-taking tendencies by looking at an association with differences in personality and in thrill-seeking. Maestripieri began by collecting saliva samples from 110 males and 91 females to determine their levels of the stress hormone cortisol and testosterone. The levels were determined before and after participants completed a computerized assessment of their predilection for financial risk aversion. The participants also talked about their own eagerness for risks and gave information about their sleep habits.

Maestripieri found that men had greater cortisol and testosterone levels than women, as expected. However, female night owls had cortisol levels similar to their male night-owl counterparts and early-morning men. Maestripieri added that high cortisol levels may be one of the biomarkers linked to greater risk-taking in night owls.

Maestripieri explained that some individuals have persistently high cortisol levels despite stress, which is known to boost cortisol for short periods of time. Greater cortisol has been connected with greater cognitive function, the professor said, and some reports reveal that high-achieving, “type-A” individuals have high cortisol levels.

More men than women think of themselves as night owls, the study discovered, and men tended to sleep less overall. Maestripieri said inclinations for being a night owl or early morning person are due partly to biology and genetic inheritance, but also can be swayed by ecological factors such as shift work or the responsibilities of child-rearing.

Gender variances in sleep patterns appear after puberty and become lesser or disappear after women reach menopause, Maestripieri said, adding that there could be an evolutionary basis.

“From an evolutionary perspective, it has been suggested that the night-owl trait may have evolved to facilitate short-term mating, that is, sexual interactions that occur outside of committed, monogamous relationships,” Maestripieri said. “It is possible that, earlier in our evolutionary history, being active in the evening hours increased the opportunities to engage in social and mating activities, when adults were less burdened by work or child-rearing.”

This theory is supported by the study's other finding: night owls are less likely to be in long-term relationships and that male night owls report a higher number of sexual partners.