Why You're More Likely To Lie When You're Tired

Feeling sluggish? Watch what you say.

We not only become less alert and productive when we get tired, but we become more likely to lie, according to a new study.

It shows that morning people become more unethical at night, and night people do the same early in the day.

Christopher M. Barnes of the University of Washington's Foster School of Business, Brian Gunia of Johns Hopkins University's Carey Business School, and Sunita Sah of Georgetown University's McDonough School of Business wanted to build upon a previous study published in Psychological Science. It concluded that the average adult has less self-control as the work day wears on, becoming more likely to act immorally by the end of the afternoon.

The team suspected that the main factor was not a long day of work that affected people but that it was their circadian rhythms, which are responsible for their sleeping habits.

Their full report will be published in Psychology Today later this year, but they summarized their findings this week in the Harvard Business Review. The team conducted two experiments to test their theory.

In the first, they gathered participants identifying themselves as both "larks" (morning people) and "owls" (night people) into a laboratory one morning and gave them a simple problem set to solve. They were told they would be paid for every problem they completed. The team also told the subjects that their problem sets were anonymous, though they were actually tracking them to see who was honest. Unsurprisingly, more night owls than larks lied to make more cash.

For the second experiment, the research team randomly assigned their subjects to a laboratory session at either 7 a.m. to 8:30 a.m. or midnight to 1:30 a.m. They were given a die to roll and were told that they would be paid more for how high their average roll turned out to be. They were not monitored, giving them anonymity. And though the team had no way of proving what numbers were rolled, statistics showed that the average for each group should be around 3.5. The results once again fit the team's theory that the less favorable time of day would lead to more unethical behavior. Here are the averages:

Larks

AM: 3.86, PM: 4.55

Owls

AM: 4.23, PM: 3.80

The team was focused on the practical ramifications of managing morning and night people, but previous neurobiology research found that the brain requires a significant amount of glucose, a type of sugar in your blood, to practice good judgment.

According to a 2007 Florida State University study published in the Personality and Social Psychology Review, "Restoring glucose to a sufficient level typically improves self-control. Numerous self-control behaviors fit this pattern, including controlling attention, regulating emotions, quitting smoking, coping with stress, resisting impulsivity, and refraining from criminal and aggressive behavior."

And it turns out that in 2009 the Stanford University School of Medicine found that circadian rhythms are directly tied to the mechanism that processes blood sugar.

Therefore, larks and owls in their less favored time of day will be operating with less glucose in their blood and will have less energy to practice self-control.

The research team who tested morning and night people think managers can use these findings in the workplace.

"Managers should try to learn the chronotype (lark, owl, or in between) of their subordinates and make sure to respect it when deciding how to structure their work. Managers who ask a lark to make ethics-testing decisions at night, or an owl to make such decisions in the morning, run the risk of encouraging rather than discouraging unethical behavior," the team writes in the Harvard Business Review.

They also advise employees looking to squeeze in an extra hour of work to add it to time of day that their body favors.