An appetite for risk is rooted in biology

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Among my women friends who are night owls, one is especially adept at taking financial risks and profiting from them. The rest of us who like staying up late, though, are notably hesitant about anything risky regarding money. The difference, reflected in several studies, may be due to the "stress hormone" cortisol.

Women who are night owls tend to be risk takers and unmarried, according to researchers at the University of Chicago. Female night owls have higher levels of cortisol than other women, closer to the levels of most men. And, according to Dutch researchers, slightly elevated cortisol in women is related to improved decision-making performance, as measured by the Iowa Gambling Task; whereas in men, the greater the elevation, the poorer the performance.

Cortisol rises in moments of high physical stress as well as in situations of uncertainty, releasing glucose and fatty acids into the blood to prepare the body for fight or flight. Cortisol levels in night-owl women are chronically elevated, and may be more so in night-owl women who are already stressed, either from past or more immediate causes.

Short-term relationships

Those people with higher cortisol levels have high metabolism, high energy and arousability, according to Dario Maestripieri, professor of Comparative Human Development at the University of Chicago. There is some evidence, he said, that high-achieving, successful people have high cortisol levels.

From an evolutionary point of view, night-owl traits might have evolved to facilitate short-term mating, which for Maestripieri's research are "sexual interactions that occur outside of committed monogamous relationships." He cited research showing that night owls of both sexes are more likely to be single or in short-term relationships. (Male night owls reported twice as many sexual partners as male early birds.)

In Maestripieri's initial study, which measured aversion to financial risk in 500 students, men were more willing to take financial risks than women. In a further study of 200 students, Maestripieri compared levels of cortisol and testosterone before and after students took a computerized test that measured their financial risk aversion. The students also described their willingness to take risks as well as their sleep patterns. The results showed that night-owl women had cortisol levels higher than other women and comparable to the levels in all men, both night owls and early risers.

In the Dutch study at the University of Utrecht, women whose cortisol levels were slightly elevated in response to stress had improved performance on decision-making and risk-taking. But among "high-cortisol responders," women had poorer performance, closer to that of men with elevated levels. High-cortisol responders of both sexes were more sensitive to immediate rewards, according to these researchers. They concluded that "acutely elevated levels of cortisol are associated with euphoria and reward-like properties related to sensation-seeking behavior."

In a British study, artificially altering cortisol levels for 20 men and 16 women by administering hydrocortisone raised levels about 70 percent, similar to those previously measured in stressed traders in the city of London. They found that "while initial spikes of cortisol had little effect on behavior, chronically high and sustained levels as seen in the traders led to a dramatic drop in participants' willingness to take risks." The researchers noted their concern that "subterranean shifts in risk appetite" could unduly affect the judgment of these traders. Also that chemical adversity to financial risk may occur unexpectedly in people taking anti-inflammatory medications such as prednisone.

The point is to be as aware as possible of how stressed you are when making important decisions, especially those involving risk. If you are an early bird with low stress, low cortisol levels might influence your thinking to make you more conservative. A laid-back night owl might be more likely to take well thought-out risks. And anyone under extreme stress, especially night owls, might make conservative decisions, based not on careful reasoning but because of the cortisol streaming through their veins.

Mary Carpenter is associate editor of MyLittleBird.com, a Washington-based women's-eye view of fashion, design and culture, where this story originally appeared.