Boys whose body mass index (BMI) increases substantially during puberty run an increased risk of stroke later in life. This is indicated by research conducted at the Sahgrenska Academy that studied over 37,000 individuals. “Our study shows that a change in BMI during puberty is an independent risk factor for stroke. However, BMI at the age of eight is not associated with any increase in risk,” says Jenny Kindblom, associate professor at the Institute of Medicine and a specialist physician at Sahlgrenska University Hospital.

She and her colleague Professor Claes Ohlsson present their study of BMI development and stroke among 37,699 men born between 1945 and 1961 in the journal Neurology. The data concerning height, weight and cases of stroke in this group are taken from school health services, conscription registers and national healthcare registers.

Rising BMI is a feature of puberty and completely normal. On average, the boys’ BMI rose by just under six units between the ages of eight and twenty. Setting the start date for puberty relatively early and the end date as much as twelve years later was done as a means by which to capture the pubertal years of all those included in the study.

The risk of stroke proved to increase by a factor of 1.21 for every further two units of BMI that were added during puberty. Someone whose BMI increased by eight units thus had a 21 per cent higher risk of stroke than an individual whose BMI increased by six units.

Broken down by blood clot in the brain or brain infarction and brain haemorrhage, the corresponding risk factors were 1.19 and 1.29, respectively.

According to the researchers, the increased risk of stroke may, at least partly, be due to increased blood pressure. The study demonstrates a clear link between a sharp increase in BMI during puberty and an increased risk of high blood pressure as an adult.

The study in question has not mapped the causes for this increased risk of stroke, but the researchers believe that it is possible to draw parallels with their earlier studies that looked at the influence of BMI change during puberty on how fat is stored in the body.

“A major increase in BMI during puberty specifically is associated with a particular risk of fat being stored as visceral or deep fat in the abdomen, which is more dangerous, and we believe that this relates to sex hormones,” says Claes Ohlsson.

“What is important here is not to let go after the early childhood years, but to continue monitoring BMI during puberty in order to detect and prevent a very large increase in weight, which is primarily the job of school health services,” he says.

In the group studied, 918 men had suffered from stroke by 2013.

The study was published in the journal Neurology.