Low blood sugar makes couples more aggressive

You've heard the term "hangry," right? People who are hungry often report being unreasonably angry until they're fed.

"Hangry" is a relatively new buzz word, but science is backing it up. A new study published in the journal PNAS suggests married couples are more aggressive when they have low blood sugar levels.

Background

Everyone gets upset at their spouse or significant other sometimes. But self-control hopefully prevents you from taking that anger out on them in a physical manner.

Yet scientists know that self-control is a limited resource. You have a tank of it, so to speak, in your brain. Each time you use self-control to avoid telling off your boss or to skip the dessert bar, that tank becomes less full.

And "aggression often starts when self-control stops," says Brad Bushman, a psychologist at Ohio State University who's studied aggression for 25 years.

What refills your self-control tank? Energy, which comes in part from the food you eat.

The study

Researchers recruited 107 married couples to participate in the study. The husbands and wives measured their glucose (or blood sugar) levels every morning and night for 21 days.

Each night they were asked to stick up to 51 pins in a voodoo doll, depending on how angry they were at their spouse. The researchers compared this aggression level to the participants' average glucose levels over the study period.

At the end of the 21 days, researchers had the couples come into the lab for another test. They asked each husband and wife to compete against their significant other in a virtual game. The couples were told the winner got to blast the loser with a loud, obnoxious noise. (In reality, their partner was not on the receiving end.)

Researchers measured how long and how intense the winner chose to blast the noise, and compared that aggression level to their average blood sugar level.

The results

Study participants with lower nightly blood sugar levels were more aggressive - both in "pinning" their voodoo doll and in blasting their partner with a louder noise for longer. These findings remained true even after researchers controlled the data for relationship satisfaction.

More evidence

This study supports previous research done by Bushman's lab at Ohio State University. In an earlier study, Bushman and his colleagues found participants who drank a sugar-sweetened beverage behaved less aggressively than those who drank a beverage sweetened with a sugar substitute.

Another study linked diabetes to more aggressive behavior. Because glucose increases self-control, people who have difficulty metabolizing glucose should have less self-control, the researchers theorized.

In a separate series of studies, Bushman showed diabetics were less inclined to forgive others. "These findings provide the first evidence that forgiveness depends on how efficiently the body uses glucose," the study authors wrote.

Takeaway

The study authors say giving people more access to food could reduce aggression in certain settings, such as prisons or psychiatric hospitals. As for the rest of us:

"I would recommend couples discuss sensitive issues over dinner," Bushman said. "Or better yet, after dinner."