"Boys who get fat in their teenage years are much more likely to suffer a life-threatening stroke as an adult, experts today warned," The Sun reports.
The study involved almost 40,000 Swedish men, who were followed from childhood through to adulthood.
Researchers found men whose weight was normal at the age of 8, but who were overweight at the age of 20, had an 80% higher risk of having a stroke compared with men whose weight remained healthy throughout their teenage years.
The good news is the researchers found overweight teen boys who managed to slim down by adulthood only had a slightly raised risk that wasn't considered to be significant.
Much of the data was taken from school and military records, which means the range of available data is somewhat limited.
Other factors that might have contributed to stroke risk, such as smoking, exercise or socioeconomic group, weren't recorded, so couldn't be taken into account.
This limitation aside, the study does add more evidence to the general consensus that being overweight increases the risk of a number of adverse health outcomes, including stroke.
If your child's overweight, there are lots of things you can do as a parent to help your child become a healthier weight, including being a good role model, getting active, and providing healthy child-sized portions.
Where did the story come from?
The study was carried out by researchers from the Centre for Bone and Arthritis Research, the Institute of Medicine, the Bioinformatics Core Facility, the Institute of Biomedicine, the Department of Molecular and Clinical Medicine, and the Sahlgrenska Academy at the University of Gothenburg in Sweden.
It was funded by the Swedish Research Council, the Swedish government, the Lundberg Foundation, the Torsten Söderberg Foundation, the Novo Nordisk Foundation, the Knut and Alice Wallenberg Foundation, and the Anna Ahrenberg Foundation. The authors reported no relevant conflicts of interest.
The Sun and the Mail Online generally covered the study accurately, but the headline "Boys who get fat as teenagers are '80% more likely to suffer a potentially deadly stroke as an adult' " doesn't provide a full picture of the results.
The 80% figure refers to males who became overweight during their teenage years and then stayed that way, compared with males who were always a healthy weight.
The researchers found overweight teens who managed to lose weight by adulthood had a raised, but not statistically significant, risk of stroke.
What kind of research was this?
This cohort study gathered data on the body mass index (BMI) of male schoolchildren. They were followed up over 50 years to see if there was an association between having a high BMI in early childhood or as an adolescent and the risk of stroke in later life.
A randomised controlled trial for this type of research – forcing boys randomised into one group to have a high BMI and the others to have an average BMI – would certainly be unethical.
What did the research involve?
Researchers gathered birth weight, childhood and adult BMI data on 37,669 male participants living in Gothenburg in Sweden.
They compared this data with stroke outcomes later in life to see if there was a link between the timing of being overweight and stroke risk.
The birth weight of all men born in Gothenburg between 1945 and 1961 was collected, as well as direct measures of height and weight taken from centrally archived School Health Care records.
They also collected height and weight data of the men at a young adult age from military conscription tests. Conscription was mandatory in Sweden until 2008.
- Childhood BMI (before puberty) was estimated at 8 years of age. Paired height and weight measurements between the age of 6.5 and 9.5 years were taken and adjusted using regression models to get the BMI at the age of 8.
- Young adult BMI was calculated at the age of 20. Paired height and weight measurements between the ages of 17.5 and 22 were taken and adjusted using regression models to get the BMI at the age of 20.
- BMI change through puberty was determined by the difference in young adult BMI and childhood BMI.
Childhood overweight was defined as a BMI of ≥17.9 kg/m2 and obesity as ≥20 kg/m2. The definition of being overweight as a young adult was a BMI ≥25 kg/m2 and obesity as ≥30 kg/m2. These definitions are standard for the measurement of BMI in children and adults.
Participants were linked to high-quality national disease registries, allowing links between the child and teen BMIs and later health outcomes. The mean follow-up from the age of 20 was 37.6 years.
The dates and diagnoses of stroke events and hypertension were taken from the National Inpatient Register and Cause of Death Register.
What were the basic results?
There were 918 stroke events, of which 672 were ischaemic strokes, 207 intracerebral haemorrhages, and 39 were undetermined.
An ischaemic stroke is where a blood clot blocks the flow of blood and oxygen to the brain. It's the most common type of stroke.
An intracerebral haemorrhage is when a diseased blood vessel within the brain bursts, allowing blood to leak inside the brain.
- For those classified as having a normal weight aged 8 and being overweight aged 20, there was an 81% increased risk of having a stroke compared with those who maintained a normal weight (hazard ratio [HR] 1.81, 95% confidence interval [CI] 1.41 to 2.33).
- For every standard deviation (two point) increase in BMI, boys were at a 21% increased risk of stroke (HR 1.21, 95% CI 1.14 to 1.28).
- For every two-point standard deviation increase in BMI, boys were at a 19% increased risk of having an ischaemic stroke (HR 1.19, 95% CI 1.11 to 1.28).
- For every two-point standard deviation increase in BMI, boys were at a 28% increased risk of having an intracerebral haemorrhage (HR 1.28, 95% CI 1.14 to 1.45).
- There was a 71% increased risk of having a stroke for boys who were overweight aged 8 and 20 (HR 1.71, 95% CI 1.22 to 2.38).
- Boys who were overweight aged 8 and a normal weight by 20 had no increased risk of stroke compared with those who maintained a normal weight.
How did the researchers interpret the results?
The researchers concluded that, "BMI increase through puberty and adolescence is associated with risk of adult ischaemic stroke and early adult intracerebral haemorrhage in men."
They proposed that, "High BMI increase during puberty might cause increased risk of adult stroke at least partly via increased blood pressure."
They further added: "The present study predates the childhood obesity epidemic and today's obesogenic environment may further enhance the observed associations with adult stroke events."
The findings of this large longitudinal cohort study seem to demonstrate a link between being overweight aged 20 and an increased risk of stroke.
This risk was regardless of whether the boy had been overweight aged 8 or not. There seemed to be no increased risk for boys who were overweight aged 8 but were a normal weight by the age of 20.
The study was conducted before the obesity epidemic, and might be even more relevant today.
But there are a number of considerations to take into account before we draw any conclusions:
- Participants were followed up until they were 52-68, so all the strokes occurred at a relatively young age. We don't know the outcomes for stroke events for the older age categories – it might be that this trend is only seen in strokes in younger people.
- The vast majority of men who had a stroke were a normal weight aged 8 and 20. This means the number of men who had a stroke in each overweight category was small – between 5 and 67 men – which reduces the reliability of these comparative results.
- The cohort was in a group of male participants in one city in Sweden. We don't know if the apparent link between high BMI in young adulthood and stroke risk applies to other populations or women.
- There are many factors other than BMI that might have influenced the results. These weren't taken into account in this study, and include socioeconomic factors in childhood or adulthood, the men's level of education, and whether they smoked or exercised.
- BMI measurements were only taken at two time points near the start of the study. It could well be that many people who were overweight aged 20 later became a normal weight, or vice versa, which might have affected the results.
Overall, the findings seem to back up the general consensus that being overweight leads to greater cardiovascular risk, including stroke.
It also suggests having a high BMI in childhood might not be much of a risk, as long as it doesn't persist into adulthood.