Sweet tea 'soothes stress'

“Psychologists have found that sweetened drinks make people less aggressive and argumentative,” according to the Daily Mail. The scientists behind the new research said a sweet drink could improve your ability to restrain your aggressive impulses during stressful meetings or commutes.

These findings come from a study where student volunteers drank lemonade sweetened with sugar or an artificial sweetener before performing stressful tasks, including preparing a speech to be read to a stranger. After the speech, some of the volunteers were provoked by being told that their speech was boring and disappointing. Those who had drunk the sugary lemonade responded to this provocation less than those who drank the artificially sweetened lemonade. The researchers suggested that this could be because the brain needs glucose for functions such as controlling behaviour.

This research used very controlled situations to provoke aggression, and it is not clear whether sugary drinks would have any effect on aggression in more stressful and complex real-life situations. Some people may feel that drinking a sugary drink makes them calmer, but they should be careful not to drink too many, as this could lead to tooth decay and weight gain.

Where did the story come from?

The study was carried out by researchers from the Universities of New South Wales and Queensland in Australia and was funded by the Australian Research Council. The study was published in the peer-reviewed Journal of Experimental Social Psychology.

The Daily Mail has reported on the research correctly and mentioned that drinking too many sugary drinks could harm your teeth. However, its headline and some of the text suggested that sugary tea may have an aggression-reducing effect, which was not specifically tested in the study.

What kind of research was this?

This was an experimental study looking at the effects of glucose consumption (a simple sugar) on aggression. The brain relies on glucose for its energy and it has been suggested that fluctuations in glucose affect ‘executive functioning’, the ability to control one’s actions. Low glucose levels have also been linked to higher levels of aggression. Therefore, the researchers were interested in finding out whether giving people glucose would reduce their levels of aggression.

The researchers in this study chose to randomly assign volunteers to receive either a sugar sweetened drink or artificially sweetened placebo drink. This process of randomisation should ensure that the groups are well balanced, and that any differences in their responses were due to the drink received.

Neither the participants nor the researchers were told which drink each person received. This should reduce the chance of a person’s beliefs about the effects of sugar influencing the results.

However, some people may have been able to detect that they were drinking an artificially sweetened drink. This could potentially affect their responses, particularly if they knew what the aim of the study was.

What did the research involve?

The researchers performed two experiments in which the undergraduate volunteers were given either lemonade sweetened with sugar, or lemonade with an artificial sweetener (the placebo). The levels of aggression displayed by the volunteers who consumed the two different drinks were then measured in aggression-provoking situations.

In the first experiment, 80 volunteers had their natural levels of aggression (called ‘trait’ aggression) assessed. They were asked to fast for three hours before the start of the study. After fasting they were randomly assigned to receive a sugary drink or not. The volunteers were then placed in a situation where an individual provoked them and they were given the chance to retaliate against the provoker by playing loud ‘white noise’ at them.

Specifically, after the drink, volunteers were given 10 minutes to write a two-minute speech on a given topic (e.g. life goals), which they were to present through a sham web conference to another ‘participant’. This participant was in fact an actor who also gave a pre-recorded two-minute speech. The volunteer then received written feedback on their speech supposedly from the actor, which suggested that it was boring and disappointing. They then participated in a test where they could deliver 25 blasts of white noise of variable length and loudness to the actor when prompted by a visual cue on the screen. The actor responded in kind with noise of increasing length and loudness.

The volunteer thought this was meant to be a test of speed of response to the visual cue. The length and loudness of the volunteer’s first noise blast was taken as a measure of their level of aggression towards the actor.

In the second experiment, 170 undergraduate volunteers were also randomised to drink a sugary or artificially sweetened drink, and to either be provoked by the actor or not. They could respond with one blast of white noise. Again, the researchers compared the length and loudness of the volunteer's noise blast to assess their level of aggression towards the actor.

What were the basic results?

The researchers found that in the first experiment, those given the sugary drink were slightly less aggressive than those given the placebo drink, although this difference was not large enough to be statistically significant. The sugary drink reduced aggression in volunteers with high levels of natural aggression more than those with lower levels of natural aggression, while the placebo drink did not.

In the second experiment, volunteers were more aggressive if they had been provoked. The researchers found that the sugary drink did not affect levels of aggression in volunteers who had not been provoked. In those who were provoked, the sugary drink reduced levels of aggression compared to the placebo drink.

As in the first experiment, the sugary drink reduced aggression in provoked volunteers with high levels of natural aggression more than in those with lower levels of natural aggression. The researchers found that among those who were not provoked, people with high levels of natural aggression who drank the sugary drink were more aggressive than those who drank the sugary drink but had low levels of natural aggression.

How did the researchers interpret the results?

The researchers conclude that giving people sugar (glucose) can reduce aggression in response to provocation, even in people with high natural levels of aggression

Conclusion

This experimental study suggests that drinking a sugary drink may reduce aggression in response to provocation in the short term, particularly in people with higher levels of natural aggression. However, this study only looked at one measure of aggression in response to provocation in very controlled, artificial scenario. When interpreting this study it is important to remember that:

• it is not clear whether a glucose drink would have any effect an aggression in more complex and stressful real-life situations
• it is unclear whether any of the undergraduate volunteers in this study would be considered to have serious problems with aggression, or problems with aggression resulting from psychiatric diagnoses
• participants fasted for three hours before the study. It is not clear whether the sugary drink would have had the same effect if they had not been fasting

Some people may feel that drinking a sugary drink makes them calmer, but people should be careful not to drink too many as this could lead to tooth decay and weight gain.