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High levels of a stress hormone linked to risk taking in those who stay up late

Night owls, people who stay up late at night, compared to early birds, people who wake up early in the morning, tend to be unmarried risk-takers.

Study author Dario Maestripieri, a professor in comparative human development at the University of Chicago, said women who are night owls share the same high propensity for risk-taking as men.

"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," Maestripieri said in a statement. "In addition, male night owls reported twice as many sexual partners than male early birds."

The researchers used data from earlier research of more than 500 graduate students at the University of Chicago Booth School of Business, which assessed financial risk aversion among male and female students and found men more willing to take financial risks than women.

However, men with high levels of the male hormone were more similar to men in financial risk-taking.

The researchers took saliva samples of 110 men and 91 women provided saliva samples to assess their levels of cortisol and testosterone. Those levels were measured before and after participants took a computerized test of their tendencies for financial risk aversion. The participants also described their own willingness to take risks and gave information about their sleep patterns.

Men had higher cortisol and testosterone levels than women; but night-owl women had cortisol levels comparable to night-owl and early-morning men.

The findings suggests high cortisol levels may be one of the biological mechanisms explaining higher risk-taking in night owls.

The link between the night-owl tendency and risky behavior could have roots in evolutionary strategies for finding mates, Maestripieri said.

"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."

The study was published in the journal Evolutionary Psychology. (UPI)