Women who were overweight in their teens and young adults may be at higher risk of stroke by age 55.

According to the American Heart Association, an ischemic stroke occurs when a blood vessel that supplies blood to the brain becomes blocked. Ischemic stroke is the most common type of stroke, accounting for about 87% of all strokes.

A Finnish study suggests that being overweight at age 14 years is associated with a later risk of thrombotic stroke in women, even if they had lost weight by age 31 years. Being overweight at age 31 years was associated with a later risk of thrombotic stroke in women, even if they had been of normal weight at age 14 years. Men who were overweight at age 14 or 31 years did not show an increased risk of thrombotic stroke. However, men who were obese at age 31 years had a higher risk of hemorrhagic stroke compared with women who were obese at age 31 years.

“Our findings suggest that being overweight can have long-term health consequences, even if the excess weight is temporary,” said Dr. Ursula Mikkola, a researcher at the Population Health Research Unit at the University of Oulu in Finland and lead author of the study. “Health professionals need to pay attention to overweight and obesity in young people and work with them to develop healthier eating and exercise habits. However, they also need to avoid adopting a stigmatizing or blaming attitude when discussing weight with teenagers and young adults.”

Researchers looked at longitudinal data from participants of the 1966 Northern Finland Birth Cohort to analyze the association between body weight at different ages and risk of stroke up to age 55. The Northern Finland Study Group was established to understand factors associated with preterm birth and infant mortality. In 1966, more than 12,000 pregnant women from two northern provinces of Finland were enrolled. Since then, more than 10,000 descendants, now in their 50s, have been followed and their health information has been used in several research studies.

In this analysis, researchers used body mass index (BMI), a ratio of weight to height, to examine whether people who were overweight or obese at age 14 or 31 had a different risk of early stroke compared with their peers who were not overweight or obese at age 14 or 31. During an average follow-up period of about 39 years after the assessment at age 14 and about 23 years after the assessment at age 31, about 1 in 20 participants experienced a stroke or transient ischemic attack (TIA, or mini-stroke) due to a blood clot. Analyses of the current study were completed in 2020.

The researchers evaluated the effect of duration of excess weight on stroke risk and found that:

• Women who were affected by obesity at age 14 were 87% more likely to have an early thrombotic or mini-stroke, and those who were obese at age 31 were 167% more likely to have a stroke than women with a healthy weight. No similar associations were seen in men.
• Obese women at age 31 had a nearly 3.5-fold increased risk of hemorrhagic stroke, and obese men at age 31 had a more than 5.5-fold increased risk of hemorrhagic stroke.
• BMI measurements taken earlier in childhood or later in adulthood did not appear to affect the results.

It's important to note that weight isn't the only health factor that affects stroke risk. There are many other factors besides weight that affect stroke risk that also need to be taken into account. “Living a healthy lifestyle (better diet, not smoking, healthy sleep, managing blood pressure, cholesterol and blood sugar levels, avoiding excessive alcohol consumption, and physical activity) can lower your risk of stroke, even if you were overweight at a young age,” added Mikola.

Researchers aren't sure why the association with an increased risk of stroke from blood clots wasn't seen in men. They are currently investigating potential causes and other risk factors in more detail.

In an accompanying editorial, Larry Goldstein, MD, FAHA, says, “This study provides further evidence of an association between overweight/obesity and stroke in young adults. However, it is tempting to assume that reducing overweight/obesity in young adults will translate into reduced stroke rates in young adults, but this remains to be proven.” Goldstein is a member of the American Heart Association Stroke Council and chair of the Department of Neurology and co-director of the Kentucky Neuroscience Institute at University of Kentucky Health Care in Lexington, Kentucky.

Study details, background and design:

• The analysis was conducted from 1980 to 2020. Participants in the analysis included 10,491 people (49% women) in their 50s. BMI was measured at age 14, 31, or both. Participants were classified as overweight or obese based on BMI using gender- and age-based criteria.
• National hospital and death registries were used to identify ischemic stroke and transient ischemic attack in people aged 14–54 years.
• Associations between BMI or change in BMI and incident stroke were identified after adjusting for participants' sex, smoking status, and education level (parents' when participants were 14 years old and when participants were 31 years old). BMI at other time points (such as BMI at 31 years old vs. BMI at 14 years old) and age at menarche in women were also considered.
• Follow-up data was maintained until participants' first stroke, death, emigration, or the end of 2020, whichever occurred first.

Limitations of this study include the analysis of health data (observational study), so it is not possible to prove a causal relationship between weight and early stroke risk. All participants were born in Finland, so the results may not be generalizable to people in other countries.

“Because strokes are rare at a young age, a difference of just a few strokes can have a huge impact on risk estimates,” said Mikola. “Also, because BMI is based only on height and weight, a high BMI can be a misleading definition of obesity; a particularly muscular person can be heavy but have very little fat.”