“Summer-born children ‘more likely to be diagnosed with depression’ than older pupils” The Independent reports.

A new study looked at a link between depression, intellectual disability and attention deficit hyperactivity disorder (ADHD) and children who are younger than others in their class at school due to being born in the summer. As the school year traditionally starts in September, children born in the summer can be up to 11 months younger than other children in their class group.

Researchers used the general practice records of more than 1 million UK children aged 4 to 15, analysing cases where children had been diagnosed with ADHD, intellectual disability, or depression. They then looked for associations between these diagnoses and a child’s age in their school year.

It found a general pattern of increasing risk with progressively younger child age. For example, the rate of ADHD was 1.5 per 1000 per school year for oldest children, born between September and November. This increased to 2 per 1000 per year for youngest children, born between June to August. Similar patterns were seen for intellectual disability and depression, though notably these diagnoses were much rarer, affecting less than 1 in 1000 children per year, no matter when they were born.

Possible reasons for these trends could be due to younger children having increased difficulties in concentrating, understanding lessons and making friends with older children. But these factors were not investigated as part of this study, so these are speculative suggestions.

Parents should be reassured that the increase in the chance of conditions such as ADHD was very small when it came to each individual child.

What the study perhaps best indicates is a need for teachers and other professionals to be aware of children who may be struggling in some way to ensure they get the support they need.

Where did the story come from?

This study was conducted by researchers from University College London. The study received no specific funding, though individual researchers received financial support from various organisations such as the Wellcome Trust. Individual researchers also declared affiliations with the British Pharmaceutical Industry and the pharmaceutical company GSK. The study was published in the peer-reviewed journal JAMA Pediatrics, and is free to access online.

While the UK media’s reporting of the study was accurate, some of the headlines were potentially alarmist.

Mail Online’s headline in particular overemphasised the findings, stating that younger children have 30% increased risk of depression because they have difficulty making friends.

Depression was the weakest link found, and the 30% relative risk does not show how small the absolute risk actually was: 0.17 per 1000 oldest children per year, increasing to only 0.22 per 1000 youngest per year.

Also, it’s not correct to assume that younger children cannot make friends with older peers. The study did not look into this issue.

What kind of research was this?

This was a cohort study using medical records from the UK general practice database to look at the link between birth period and diagnoses of mental health conditions.

Observational studies can look at the link between potential risk factors or exposures and health outcomes. However, they cannot prove cause and effect and fully assess the range of contributing factors that could be involved in the relationship.

What did the research involve?

The study accessed records from more than 700 general practices contributing to the UK Clinical Practice Research Datalink and identified children aged 4 to 15 who had been registered before January 2017.

They looked at each child’s month of birth and calculated their relative age according to the school year, which runs 1 September to 31 August in England and Wales (school intakes in Northern Ireland and Scotland are different). Children were divided into 4 categories of 3 months, such as children born between September and November.

The researchers looked at the link between school age and diagnoses of ADHD, intellectual disability and depression. They adjusted their statistical models for potential confounders of gender, socioeconomic status and calendar year.

What were the basic results?

The study included 1,042,106 children aged 4 to 15 years. It excluded those with mental health diagnoses prior to school entry.

ADHD

The rate of ADHD ranged from 1.54 per 1000 oldest children (born September to November) per year, to 2.08 per 1000 youngest children (born June to August) per year. The risk of ADHD compared with the oldest children:

• 15% increased risk for December to February birthdays (hazard ratio [HR] 1.15, 95% confidence interval [CI] 1.08-1.23)
• 31% for March to May birthdays (HR 1.31, 95% CI 1.23-1.40)
• 36% for June to August birthdays (HR 1.36, 95% CI 1.28-1.45)

Intellectual disability

The rate ranged from 0.74 per 1000 oldest children per year to 0.96 per 1000 youngest children per year, again with progressive risk increase:

• 6% increased risk for December to February birthdays (HR 1.06, 95% CI 0.96-1.17)
• 20% for March to May birthdays (HR 1.20, 95% CI 1.09-1.32)
• 30% for June to August birthdays (HR 1.30, 95% CI 1.18-1.42)

Depression

The relationship was not so strong. The rate for the first three groups of children (born September to May) was similar, at around 0.17 to 0.19 per 1000 per year, with no difference in risk. Only the youngest children (born June to August) had a slightly higher rate of 0.22 per 1000 per year with 31% increased risk (HR 1.31, 95% CI 1.08 to 1.59).

Overall the researchers estimated that being the youngest in the year may account for 23% of the cases of depression and intellectual disability in children born June to August, and 26% of cases of ADHD.

How did the researchers interpret the results?

The researchers conclude “relative youth status in the school year is associated with an increased risk of diagnosis of ADHD, intellectual disability and depression in childhood. Further research into clinical and policy interventions to minimise these associations appears to be needed.”

Conclusion

The study appears to show a clear link between children being progressively younger in their school year and their increased risk of ADHD or intellectual problems. This relationship seems plausible. It’s often been recognised that some children who may be almost a whole year younger than others in their class at school may understandably find it harder to keep up with lessons or be more likely to be distracted.

There are some things to keep in mind:

• even for ADHD, the most common condition, the incidence remains low, regardless of your age. Ranging from 1.5 per 1000 oldest children per school year to 2 per 1000 youngest per year. Therefore, very few children are going to have problems resulting in a medical diagnosis.
• both intellectual disability and depression were rare, affecting less than 1 in 1000 per year. They also covered a very wide range of diagnostic codes in the database. For example, intellectual disability ranged from “learning difficulties” to “feeble mindedness” to “mental retardation”. Depression codes included “brief depressive reaction”, “post-viral” and “seasonal” to more major episodes. You can only make very general conclusions from such broad groupings.
• related to this, it’s very hard to prove cause and effect. You cannot account for the wide range of hereditary, lifestyle and environmental factors that may have contributed to risk of these diagnoses.
• the study covered children across full school age from reception to school leaving age. Therefore, it’s not possible to say when children were more likely to experience problems (if any). For example, whether in the early school years or later in senior school.
• the study cannot account for milder cases of attention or learning problems that have not reached medical attention.

In terms of implications, however, they may be limited. The cut-off intake for the school year has to start and end somewhere. One expert has suggested school years should split their classes according to the age of children within the year, but this may not always for feasible or appropriate on a general basis.