Low levels of blood sugar can increase the risk of irritation with your partner turning into a blazing row, according to a study suggesting a physiological basis for marital disharmony.
Scientists found that blood glucose levels could predict whether someone was likely to feel angry enough with a spouse to secretly stick pins in a voodoo doll, meant to represent them, in psychological tests.
People with low glucose levels were also more likely than individuals with high levels of glucose to blast their partners with loud noise if they competed against them in a game, according to a second experiment.
The findings support the theory that hungry people are more likely than well-fed individuals to be angry. They also provide a scientific basis for suggesting that diet may play an important role in situations where people spend time together, whether at home, in schools or in prisons.
"People can relate to this that when they get hungry, they get cranky. We found that being 'hangry' – hungry and angry – can affect our behaviour in a bad way, even in our most intimate relationships," said Professor Brad Bushman of Ohio State University in Columbus, Ohio.
The three-year study involved 107 married couples, who were assessed for their general relationship satisfaction in order to see how happy they were with one another overall.
Over a period of 21 days, each couple monitored their blood glucose levels in the morning and evening and were given a voodoo doll and 51 pins, which they were supposed to stick in the doll when they were on their own, depending on how angry they felt towards their spouse.
The study, published in the journal 'Proceedings of the National Academy of Sciences', showed a clear link between low levels of blood glucose and the number of pins a spouse stuck into the voodoo doll, Professor Bushman said.
"Even those who reported they had good relationships with their spouses were more likely to express anger if their blood glucose levels were lower," he said.
In a second experiment after the 21-day period, the couples took part in a laboratory test where they played a computer game against their partner, allowing the winner to blast their spouse with a loud noise through headphones.
In fact, the scientists had arranged it so that each individual played against a computer rather than their spouse without their knowing it, so that they were sure to lose about half the games they played.
Again, when blood sugar levels fell, individuals were more likely to give longer and louder blasts of noise than when sugar levels were higher.
Comparing the first and second part of the study, the scientists also found that those people who stuck more pins in the dolls were more likely to show real aggression as louder and longer noises.