Wondering when's the best time of day to make a big decision? Forget the astrology charts and drink a cup of coffee—or four.

You make better decisions when you have a full bladder, or so says a study to be published in Psychological Science, a journal of the Association for Psychological Science.

In one experiment, researchers from the Netherlands had participants either drink five cups of water or take small sips of water from five separate cups. After about 40 minutes—the time it takes for water to reach the bladder—researchers tested the subjects' self control. Participants were asked to make eight choices: each was between receiving instant gratification (or near instant) versus a larger—but deferred—reward. For example, in one scenario they could opt for picking up $16 the next day or $30 in 35 days. The people with full bladders were more likely to opt for the larger rewards later. Other experiments backed up the link.

"You seem to make better decisions when you have a full bladder," said lead researcher Mirjam Tuk, of the University of Twente in the Netherlands. (Science Daily suggests this may be a reason for stores that count on impulse buys to allow customers to use the bathroom, "since they might be more willing to go for the television with the bigger screen when they have an empty bladder.")  

It's a surprising find: Tuk wrote in the paper's abstract that psychologists believe that "visceral states are known to have a [detrimental] impact on our ability to exert self control." In psych-speak this is called "ego-depletion"—the mind struggles to restrain a bodily function, making it easier to exert self-control in other areas.

So what's going on in the case of a full bladder prompting better decisions? Tuk's hypothesis is that—because feelings of inhibition all originate from the same area of the brain—self-control in one area can affect self-control in others. "People who [are experiencing] higher levels of bladder control should be better able to control unrelated impulses," she wrote in an email to CNN.

Wondering what prompted Tuk to study the subject? Too many cups of coffee as she tried to stay awake during a long lecture.

When do you make your important decisions?