Childhood head injury linked to range of adult healt...

"Millions of Brits face dying early because of something they did when they were children," says the Daily Mirror's needlessly alarming headline.

The newspaper reports on a study which found that a head injury causing concussion (known as a traumatic brain injury or TBI) may increase the chances of a range of health problems in later life.

The study used Swedish databases to follow more than a million people for up to 41 years. Nine percent of them had been treated in hospital for a TBI before they were 25.

After adjusting their figures to account for family circumstances, the researchers found those who'd had a head injury were slightly more likely to:

be receiving a disability pension
have been treated for psychiatric illness
not have secondary school qualifications
have died before the age of 41

Older children, those with more severe head injuries, and those who had more than one head injury were more likely to be affected.

The study doesn't prove that the head injuries caused the problems.

It's possible that factors the researchers didn't measure had an effect. For example, children with behavioural problems may be both prone to childhood accidents as well as more likely to experience difficulties in adulthood.

When it comes to head injuries, prevention is better than any cure. But it is also important not to discourage your child from taking part in physical activity, as this brings a much greater risk of health problems in adulthood.

Where did the story come from?

The study was carried out by researchers from Oxford University, Imperial College London, Indiana University, and the Karolinska Institute in Sweden. It was funded by the Wellcome Trust, the Swedish Research Council and National Institute for Child Health and Human Development.

The study was published in the peer-reviewed journal PLOS Medicine on an open-access basis, so it is free to read online.

The Times, Mirror and Daily Mail headlines all focused on the increased risk of early death after childhood concussion, although this outcome had the lowest absolute risk of all those studied. The researchers analysed their figures three ways, with different levels of accounting for confounding factors, including family circumstances. Perhaps unsurprisingly, the newspapers used the figures which showed the biggest increase in risk, not the ones that took full account of this confounding.

However, the newspapers did quote experts who cautioned there is a need to balance the risks of injury from sports such as rugby and football against the benefits of taking part in sport. The Mirror's extrapolation that "millions of Britons" are at risk of early death seems a bit over-done, although up to 700,000 children are apparently treated for head injury in the UK each year.

What kind of research was this?

This was a cohort study, using a national database of births in Sweden. These studies are good ways to find links between factors, in this case head injury in childhood or early adulthood, and a range of outcomes including poor educational achievement, inability to work on health grounds, and early death. However, they cannot prove that one causes the other.

What did the research involve?

Researchers followed up 1,143,470 people born between 1973 and 1985 in Sweden. They used Sweden's database system to check whether they'd been treated for a brain injury that caused concussion, before the age of 25. They then looked at a range of outcomes in adulthood, including poor educational achievement and early death. After adjusting their figures to take account of people's family circumstances, they looked to see whether people who'd had a head injury were more likely to have one of these outcomes.

Family circumstances, including deprivation, parental education level and environment, can affect both the chances of having a head injury and the chances of one of the long-term outcomes being measured. Therefore the researchers also looked at what happened to the brothers or sisters of children with head injury, to see whether they were more or less likely to have had one of these outcomes.

They calculated the risk of the outcomes for people with and without head injury in early life using three models. First they just adjusted for sex, year of birth and order in which children were born. In the second model they also adjusted for family circumstances such as income and parental education. Finally, they performed further adjustments to take account of what happened to siblings of children with head injuries. The figures we report in the results section below are the third set of figures, as they are likely to be the least affected by confounding factors.

Researchers also calculated the absolute risks of the different outcomes, and looked at the effects of the severity of injury, age of injury and repeated injury.

What were the basic results?

Of more than a million people studied, 104,290 (9.1%) had been treated for a head injury. Looking at the people injured compared to 55,831 siblings who had not had head injuries:

6.3% received a disability pension, compared to 5.5% of unaffected siblings
20% had an outpatient psychiatric visit (10.4% were admitted to psychiatric hospital), compared to 18.4% of unaffected siblings (9% were admitted to psychiatric hospital)
1.6% had died before age 41, compared to 1.4% of unaffected siblings
13.9% didn't pass secondary school qualifications, compared to 12.5% of unaffected siblings

These figures translate into increased relative risks which look high, though the overall difference between people with and without head injury is small, as shown above. For each outcome, the results are:

49% increased risk of disability pension (relative risk (RR) 1.49, 95% confidence interval (CI) 1.38 to 1.6)
31% increased risk of outpatient psychiatric visit (RR 1.31, 95% CI 1.26 to 1.37)
57% increased risk of admission to psychiatric hospital (RR 1.57, 95% CI 1.47 to 1.67)
40% increased risk of death before age 41 (95% CI 1.16 to 1.68)
28% increased risk of low educational achievement (95% CI 1.23 to 1.33)

In addition, the results showed that having a severe head injury increased the risk of any of these outcomes, as did having more than one head injury.

How did the researchers interpret the results?

The researchers say their results "indicate potentially causal effects" between head injury in childhood and problems later in life. They say this implies a need to prevent head injury, through better parental supervision of young children and prevention of sports-related concussion for older children. This "could focus on changes to rules so that risks of players colliding their heads with each other or with equipment", including heading footballs, is reduced, they say.

Less controversially, they call for age-appropriate follow-up of children who've had head injuries, to try to prevent them from falling behind at school, and to take action on signs of health or social problems.

Conclusion

This is an important study, but the more alarming headlines over-state the absolute risks of problems in adulthood following on from a childhood head injury. The majority of people who'd had a head injury didn't have any of the problems studied, and the overall risk of death by age 41 – the outcome that got most press attention – was 1.6% – only 0.2 percentage points higher than for the unaffected siblings of children with head injury.

The study has a number of strengths:

it is very large
has a long follow-up period
the Swedish database records are thought to be accurate
it includes figures about siblings of children with head injury, helping to account for some of the differences seen with family upbringing, although they can't account for everything

Some experts questioned whether neurodevelopmental disorders such as attention deficit hyperactivity disorder (ADHD) might increase both the risk of head injury and of the adverse outcomes in adulthood. However, the researchers say they took account of psychiatric and neurological conditions that occurred before age 25, and that this did not affect the results.

As various experts have warned, the risk of head injury should not be used as a reason for children not to take part in activities such as sports. We don't know from the study whether the injuries were sports-related, and we do know that physical activity has many benefits, including in the fight against childhood obesity.

Perhaps the most important conclusion from the study is that children and young people who've had a concussion should be monitored for signs of problems later in life, so that they can be helped to avoid some of the potential consequences.