University of Cambridge researchers said when traders have high morning testosterone levels they make more than average profits for the rest of that day.

The scientists hypothesize that this may be because testosterone has been found to increase confidence and appetite for risk.

The researchers tracked 17 London male traders for eight business days and measured their hormones using saliva samples twice a day at 11:00 a.m. and 4:00 p.m. -- before and after most of the day's trading.

The study found the traders experienced acute raised cortisol -- a stress hormone that heightens memory for adverse events -- in association with higher volatility in the markets.

Cortisol is likely to rise in a market crash and, by increasing risk aversion, to exaggerate the market's downward movement. Testosterone is likely to rise in a bubble and, by increasing risk-taking, to exaggerate the market's upward movement.

The study, published in the Proceedings of the National Academy of Sciences, found the steroid feedback loops may help explain why people caught up in bubbles and crashes often find it difficult to make rational choice.