“Being bullied regularly by a sibling could put children at risk of depression when they are older,” BBC News reports.

A new UK study followed children from birth to early adulthood. Analysis of more than 3,000 children found those who reported frequent sibling bullying at age 12 were about twice as likely to report high levels of depressive symptoms at age 18.

The children who reported sibling bullying were also more likely to be experiencing a range of challenging situations, such as being bullied by peers, maltreated by an adult, and exposed to domestic violence. While the researchers did take these factors into account, they and other factors could still be having an impact. This means it is not possible to say for certain that frequent sibling bullying is directly causing later mental health problems. However, the results do suggest that it could be a contributor.

As the authors suggest, interventions to target sibling bullying, potentially as part of a programme targeting the whole family, should be assessed to see if they can reduce the likelihood of later psychological problems.

Where did the story come from?

The study was carried out by researchers from the University of Oxford and other universities in the UK. The ongoing cohort study was funded by the UK Medical Research Council, the Wellcome Trust and the University of Bristol, and the researchers also received support from the Jacobs Foundation and the Economic and Social Research Council.

The study was published in the peer-reviewed medical journal Pediatrics. The article has been published on an open-access basis so it is available for free online.

This study was well reported by BBC News, which reported the percentage of children in each group (those who had been bullied and those who had not) who developed high levels of depression or anxiety. This helps people to get an idea of how common these things actually were, rather than just saying by how many times the risk is increased.

What kind of research was this?

This was a prospective cohort study that assessed whether children who experienced bullying by their siblings were more likely to develop mental health problems in their early adulthood. The researchers say that other studies have found bullying by peers to be associated with increased risk of mental health problems, but the effect of sibling bullying has not been assessed.

A cohort study is the best way to look at this type of question, as it would clearly not be ethical for children to be exposed to bullying in a randomised way. A cohort study allows researchers to measure the exposure (sibling bullying) before the outcome (mental health problems) has occurred. If the exposure and outcome are measured at the same time (as in a cross sectional study) then researchers can’t tell if the exposure could be contributing to the outcome or vice versa.

What did the research involve?

The researchers were analysing data from children taking part in the ongoing Avon Longitudinal Study of Parents and Children. The children reported on sibling bullying at age 12, and were then assessed for mental health problems when they were 18 years old. The researchers then analysed whether those who experienced sibling bullying were more at risk of mental health problems.

The cohort study recruited 14,541 women living in Avon who were due to give birth between 1991 and 1992. The researchers collected information from the women, and followed them and their children over time, assessing them at intervals.

When the children were aged 12 years they were sent a questionnaire including questions on sibling bullying, which was described as “when a brother or sister tries to upset you by saying nasty and hurtful things, or completely ignores you from their group of friends, hits, kicks, pushes or shoves you around, tells lies or makes up false rumours about you”. The children were asked whether they had been bullied by their sibling at home in the last six months, how often, what type of bullying and at what age it started.

When the children reached 18 they completed a standardised computerised questionnaire asking about symptoms of depression and anxiety. They were then categorised as having depression or not and any form of anxiety or not, based on the criteria in the International Classification of Diseases (ICD 10). The teenagers were also asked whether they had self-harmed in the past year, and how often.

The researchers also used data on other factors that could affect risk of mental health problems, collected when the children were eight years of age or younger (potential confounders), including any emotional or behaviour problems at age seven, the children’s self-reported depressive symptoms at age 10, and a range of family characteristics. They took these factors into account in their analyses.

What were the basic results?

A total of 3,452 children completed both the questionnaires about sibling bullying and mental health problems. Just over half of the children (52.4%) reported never being bullied by a sibling, just over a tenth (11.4%) reported being bullied several times a week, and the remainder (36.1%) reported being bullied but less frequently. The bullying was mainly name calling (23.1%), being made fun of (15.4%), or physical bullying such as shoving (12.7%).

Children reporting bullying by a sibling were more likely to:

• Be girls
• To report frequent bullying by peers
• To have an older brother
• To have three or more siblings
• To have parents from a lower social class
• To have a mother who experienced depression during pregnancy
• To be exposed to domestic violence or mistreatment by an adult
• To have more emotional and behavioural problems at age seven

At 18 years of age, those who reported frequent bullying (several times a week) by a sibling at age 12 were more likely to experience mental health problems than those reporting no bullying:

• 12.3% of the bullied children had clinically significant depression symptoms compared with 6.4% of those who were not bullied
• 16.0% experienced anxiety compared with 9.3%
• 14.1% had self-harmed in the past year compared with 7.6%

After taking into account potential confounders, frequent sibling bullying was associated with increased risk of clinically significant depression symptoms (odds ratio (OR) 1.85, 95% confidence interval (CI) 1.11 to 3.09) and increased risk of self-harm (OR 2.26, 95% CI 1.40 to 3.66). The link with anxiety did not reach statistical significance after adjusting for potential confounders.

How did the researchers interpret the results?

The researchers concluded that “being bullied by a sibling is a potential risk factor for depression and self-harm in early adulthood”. They suggest that interventions to address this should be designed and tested.

Conclusion

The current study suggests that frequent sibling bullying at age 12 is associated with depressive symptoms and self-harm at age 18. The study’s strengths include the fact that it collected data prospectively using standard questionnaires, and followed children up over a long period. It was also a large study, although a lot of children did not complete all of the questionnaires.

The study does have limitations, which include:

• As with all studies of this type, the main limitation is that although the study did take into account some other factors that could affect the risk of mental health problems, they and other factors could still be having an effect.
• The study included only one assessment of bullying, at age 12. Patterns of bullying may have changed over time, and a single assessment might miss some children exposed to bullying.
• Bullying was only assessed by the children themselves. Also collecting parental reports, or those of other siblings, might offer some confirmation of reports of bullying. However, bullying may not always take place when others are present.
• The depression assessments were by computerised questionnaire, this is not equivalent to a formal diagnosis of having depression or anxiety after a full assessment by a mental health professional, but does indicate the level of symptoms a person is experiencing.
• A large number of the original recruited children did not end up completing the questionnaires assessed in the current study (more than 10,000 of the 14,000+ babies starting the study). This could affect the results if certain types of children were more likely to drop out of the study (e.g. those with more sibling bullying). However, the children who dropped out after age 12 did not differ in their sibling bullying levels to those who stayed in the study, and analyses using estimates of their data did not have a large effect on results. Therefore the researchers considered that this loss to follow-up did not appear to be affecting their analyses.

While it is not possible to say for certain that frequent sibling bullying is directly causing later mental health problems, the study does suggest that it could be a contributor. It is also clear that the children experiencing such sibling bullying are also more likely to be experiencing a range of challenging situations, such as being bullied by peers, maltreated by an adult, and exposed to domestic violence.

As the authors say, the findings suggest that interventions to target sibling bullying, potentially as part of a programme targeting the whole family, should be assessed to see if they can reduce the likelihood of later psychological problems.

Read more about bullying, how to spot the signs and what to do if you suspect your child is being bullied (or is a bully themselves).

Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.

Summary

“Being bullied regularly by a sibling could put children at risk of depression when they are older,” BBC News reports. A new UK study followed children from birth to early adulthood. Analysis of more than 3,000 children found.

Links to Headlines

• Sibling bullying increases depression risk. BBC News, September 8 2014
• Lasting toll of bullying by a sibling: Brothers or sisters who are regularly picked on ‘more likely to be depressed or take an overdose’. Daily Mail, September 9 2014

Links to Science

• Bowes L, Wolke D, Joinson C, et al. Sibling Bullying and Risk of Depression, Anxiety, and Self-Harm: A Prospective Cohort Study. Published online September 8 2014