Iris Blandón-Gitlin of California State University in Fullerton and her colleagues asked 22 students to complete a questionnaire on controversial social or moral issues. They were then interviewed by a panel, but instructed to lie about their opinions on two issues they felt strongly about. After completing the questionnaire, and 45 minutes before the interview, in what they were told was an unrelated task, half drank 700 ml of water and the other half 50 ml.
The interviewers detected lies less accurately among those with a full bladder. Subjects who needed to urinate showed fewer signs that they were lying and gave longer, more detailed answers than those who drank less.
The findings build on work by Mirjam Tuk of Imperial College London, whose study in 2011 found that people with full bladders were better able to resist short-term impulses and make decisions that led to bigger rewards in the long run. These findings hinted that different activities requiring self-control share common mechanisms in the brain, and engaging in one type of control could enhance another.