Eating chocolate probably won’t save your marriage

10:20am Tuesday 15th April 2014

content supplied by NHS Choices

"As blood glucose levels plummet, aggression levels rise, and people take it out on those closest to them," The Daily Telegraph reports.

This news is based on an American study into blood glucoses levels and aggression.

Researchers aimed to find out whether people's blood glucose levels predicted aggressive impulses and aggressive behaviour in married couples.

The thinking behind the study is that as people's energy levels fall, so does their self-control, making them more likely to lash out (either verbally or physically) to those closest to them. The study included 107 couples, who had their blood sugar measured over 21 days. The researchers measured aggressive impulses by allowing participants to stick pins in a voodoo doll each evening. They were told that the angrier they felt towards their partner, the more pins they should stick in (up to a total of 51!).

Aggressive behaviour was assessed by measuring the intensity and duration of an unpleasant sound (such as fingernails scratching across a blackboard) that one partner selected for the other as a punishment for losing a competition at the end of the study.

The researchers did find an association between blood glucose levels and increased results in the tests used to assess aggressive impulses and aggressive behaviour.

However, this was a highly experimental and abstract study, and it is difficult to assess what, if any, implications it has in a real world setting. It is certainly not the case, as the Daily Express claims, that "chocolate can save your marriage".

If you are concerned that your relationship has become abusive - either verbally, physically, or both - call the free 24-hour National Domestic Violence Helpline on 0808 2000 247.

Where did the story come from?

The study was carried out by researchers from The Ohio State University, University of Kentucky and University of North Carolina. It was funded by a US National Science Foundation Grant and published in the peer-reviewed journal PNAS.

Despite headlines to the contrary, the study did not show that "chocolate can save your marriage". It also didn't show that married couples who diet are more likely to argue, or that "low levels of blood sugar can increase the risk of a niggling irritation with your partner turning into a blazing row".

All that it found was that the lower blood glucose levels were, the more pins participants stuck into the voodoo doll, and the greater the intensity and duration of noise participants set for their spouse as a forfeit for losing a competition.

There are also a number of limitations to the study, which should be considered. The researchers didn't determine whether the participants were hungry or whether they were dieting at any stage of the study. They also failed to investigate whether having a sugary snack before completing either the voodoo doll or trial tasks changed the outcome. They also didn't examine whether the participants had impaired glucose tolerance (a marker of diabetes).

Despite the light-hearted coverage, it is important to state that domestic violence is a serious issue that can affect both men and women. Read more advice for people in abusive relationships.

 

What kind of research was this?

This was an experimental study that aimed to determine whether evening blood sugar (glucose) levels predict aggressive impulses and aggressive behaviour in married couples.

The researchers measured aggressive impulses by allowing participants to stick pins in a voodoo doll, and aggressive behaviour by measuring the intensity and duration of an unpleasant sound that participants selected as the forfeit for their spouse losing a competition.

The researchers wanted to test how low blood glucose levels may relate to violent tendencies among intimate partners. It is unclear how the results of this highly experimental scenario can be applied to actual relationships where domestic violence occurs.

 

What did the research involve?

The researchers recruited 107 married couples to take part in the study. The average age of participants was 36, with an average marriage of 12 years in length, and were given $50 each to take part in the study. The researchers do not say whether any of the couples had any previous experience of intimate partner violence.

For 21 days, participants measured their blood glucose levels in the morning before breakfast and in the evening before bedtime. Each evening, participants were told to stick between 0 and 51 pins into a voodoo doll that represented their husband or wife, depending on how angry they were with them. Participants were told to do this alone, without their spouse present, and to record the number of pins inserted. The researchers say this was a measure of "aggressive impulses".

At the end of the trial, each couple competed against their husband or wife on a task involving 25 trials at the laboratory. The winner of each trial could blast the loser with a loud noise (a mixture of unpleasant noises, such as fingernails on a chalkboard, dentist drills and ambulance sirens) through headphones. The winner could also choose the intensity (between 60 decibels - similar to the noise level of laughter -and 105 decibels - the level of a fire alarm) and the duration (between half a second and five seconds). They could also choose not to blast their spouse with noise.

The researchers measured the intensity and duration of noise participants set for their spouse. However, unbeknown to them, participants actually competed against a computer. Participants lost 13 of the 25 trials (in a randomly determined order) and heard noise on each of those 13 trials. The computer chose random noise intensity and duration levels for the spouse across the 25 trials. The researchers state that this was a measure of "aggressive behaviour".

The researchers aimed to see if there was a link between glucose levels and "aggressive impulses" (the number of pins participants stuck in the voodoo doll), and whether there was a link between glucose levels and "aggressive behaviour" (the intensity and duration of noise participants set for their spouse).

 

What were the basic results?

The researchers found that the lower the level the blood glucose level, the more pins participants stuck into the voodoo doll.

Lower-than-average evening glucose levels were linked to longer and more intense noise used to blast their spouse with after winning trials.

People who stuck more pins into the voodoo doll across the 21 days also selected louder and longer noise blasts for their spouse.

 

How did the researchers interpret the results?

The researchers said: "Our study found that low glucose levels predicted higher aggressive impulses in the form of stabbing pins in a voodoo doll that represented a spouse. This study also found that low glucose levels predicted future aggressive behaviour [sic] in the form of giving louder unpleasant noise blasts for longer durations to a spouse."

"There also was a link between aggressive impulses and aggressive behaviour. Lower levels of glucose predicted aggressive impulses, which, in turn, predicted aggressive behaviour. These findings remained significant even after controlling for relationship satisfaction and participant sex. Thus, low glucose levels might be one factor that contributes to intimate partner violence."

 

Conclusion

This study of married couples found that the lower blood glucose levels were in the evening, the more pins participants stuck into a voodoo doll of their husband or wife. Lower blood glucose was also associated with selecting longer and more intense noise to blast their spouse with after winning trials.

The real-life implications of these findings are unclear. The researchers wanted to test how low blood sugar levels relate to increased violent tendencies towards a partner. It is already known that very low blood glucose can cause symptoms including altered and irrational behaviour (which may include aggression), but this is usually seen in people with diabetes whose blood sugar drops very low, usually below three or four millimoles per litre (known as hypoglycaemia). The actual blood sugar levels of participants in this study were not reported, and as none were reported to have diabetes or impaired glucose tolerance, it is highly unlikely that glucose levels in any of the participants had fallen to a level where you would expect to see such symptoms.

Most importantly, this study used highly experimental scenarios, where married couples (with no reported experience of partner violence) were asked to carry out two abstract tests. Therefore, the results cannot be applied to real life situations involving domestic violence. 

Intimate partner violence may have varied complex psychological causes, and it cannot be answered by one general simple cause, such as low blood sugar.

If you find it difficult to keep aggressive emotions in check and frequently lash out at those around you, you may require anger management training. Read more advice about controlling your anger.

Analysis by Bazian. Edited by NHS ChoicesFollow Behind the Headlines on TwitterJoin the Healthy Evidence forum.

Summary

"As blood glucose levels plummet, aggression levels rise, and people take it out on those closest to them," The Daily Telegraph reports.

Links to Headlines

Married couples who diet more likely to argue, study finds. The Daily Telegraph, April 14 2014

Spoiling for a row? Then check your sugar level. The Independent, April 15 2014

How chocolate can save your marriage. Daily Express, April 15 2014

Links to Science

Bushman BJ, DeWall CN, Pond RS, et al. Low glucose relates to greater aggression in married couples. PNAS. Published online April 14 2014

 

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