Childhood can strongly influence the rest of a person’s life. This is clear in a new Danish study showing that the taller a child is at 7–13 years old, the lower the risk of stroke – a blocked or ruptured blood vessel in the brain – later in life. Although people have become taller on average today than they were 50 years ago, the association remains the same. The researchers do not know the reasons, but they think that doctors should take height into account when they assess risk.
Whether they are the tallest or the shortest person in a class means a lot to most children. Later in life, very few people remember whether they were among the tallest in their class when they were 7 years old. A new Danish study, however, shows that this factor is important. Schoolchildren’s height is directly associated with the risk of ischaemic or intracerebral haemorrhagic stroke – a blocked or ruptured blood vessel in the brain – later in life.
“We found a very strong and yet very surprising association: the taller you are at age 7 years , the lower the risk of these two types of stroke when you get older. Since genes determine about 80% of our height, the genes that make us tall could probably play a part in the increasing the risk of stroke – especially because the association between childhood height and later stroke has not changed during a period in which children’s average height has increased. Nevertheless, height and growth in height are not obvious targets for intervention, but doctors assessing risk should still consider the increased risk of stroke among people who were short as children,” explains a main author, Line Klingen Gjærde, a doctor and PhD student at Frederiksberg Hospital.
Different associations for girls and boys
The study is the largest of its kind, including data from 310,000 boys and girls, born 1930 to 1989, in the Copenhagen School Health Records Register. Of these, 13,000 had a stroke as adults. Unsurprisingly, 60% of the 13,000 who had a stroke were men, but the strong association between their childhood height and risk of stroke was surprising.
“Previous studies have indicated that childhood height was associated with stroke, but these were small in size and included only women and men born in the first half of the 20th century. We were therefore interested in determining whether we would find the same association for people born more recently, since the major changes in people’s diets and living circumstances in general could have affected the associations. We were also very interested in whether the association would be present for both women and men.”
The results were very clear. Women who had been among the shortest 20% at age 7 years had more than a 20% higher relative risk of having a blocked blood vessel in the brain later in life. The risk among men was slightly higher: 24%. Men had about 35% greater relative risk of having a ruptured blood vessel in the brain if they had been among the shortest boys at age 7 years. Women who had been short at 7 years, however, had no increased risk of this type of stroke.
“The most interesting finding was that the linear association between height and stroke remained intact over time: the association is the same for people born in the 1930s and for people born in the 1970s and 1980s. Thus, although the average height increased substantially in this period, the risk of stroke among those who had been short in childhood was still high.”
Only a statistical association so far
Another interesting perspective of the study was that the risk of stroke later in life was associated with height already at age 7 years. So even if children grew more than expected from 7 to 13 years (that is, crossed height percentiles), their height at 7 years was still associated with their risk.
“This is naturally very difficult to explain, but it is probably related to manifestations of people’s genetic material. Thus, some genes may influence both height and the risk of stroke.”
Although height as a child and stroke later in life are associated statistically, the researchers are very cautious about stating that this association is causal. Nevertheless, despite this reservation, the results call for more research into the underlying mechanisms of the associations.
More research is needed to determine the exact nature of this association. We might be able to find a causal link with specific genes or perhaps a physiological link, but in any case, knowing that people who were shorter as children have a higher risk of stroke may be important when assessing overall risk of stroke.
“Childhood stature and growth in relation to first ischemic stroke or intracerebral haemorrhage” has been published in Stroke. The authors are employed at the Novo Nordisk Foundation Center for Basic Metabolic Research.