Lower cognitive function during teenage years may significantly increase the risk of having a stroke before the age of 50, according to a new study published in the Journal of Epidemiology & Community Health. Researchers found that adolescents with medium and low cognitive function had a twofold and threefold increased risk, respectively, of early-onset stroke compared to their peers with higher cognitive function, even after accounting for various other risk factors.
The study was driven by a rising concern over the increasing incidence of stroke among adults under 50 years old. While stroke is generally associated with older adults, younger individuals are experiencing higher rates of this debilitating condition. This trend underscores the importance of identifying early-life risk factors that might contribute to stroke later in life.
Cognitive function during adolescence was of particular interest because lower cognitive function has been linked to other health issues like hypertension and obesity, which are known stroke risk factors. The researchers aimed to clarify whether cognitive function in adolescence could be a predictor of early-onset stroke.
This study involved a nationally representative cohort of 1.7 million Israeli adolescents who underwent extensive evaluations before mandatory military service between 1987 and 2012. These evaluations included a general intelligence test comprising four subtests: understanding and carrying out verbal instructions, verbal abstraction and categorization, mathematical abilities, and non-verbal abstract reasoning and visual-spatial problem-solving. The results of these subtests were combined to form a general cognitive function score on a nine-point scale, which was then categorized into three groups: low (scores 1-3), medium (scores 4-7), and high (scores 8-9).
The researchers linked this cognitive data with stroke incidence data from the Israeli National Stroke Registry, which has recorded all stroke cases in Israeli hospitals since 2014. They excluded individuals with missing cognitive performance data or those who died before 2014, resulting in an analytical sample of 1,741,345 individuals. They tracked the participants for stroke events from 2014 until 2018, controlling for various factors including body mass index (BMI), educational attainment, socioeconomic status, and diabetes status.
The researchers found that adolescents with medium cognitive function had a 1.78 times higher risk of experiencing any stroke before the age of 50, while those with low cognitive function had a 2.68 times higher risk, compared to their peers with high cognitive function.
When the analysis was narrowed to ischemic strokes specifically, the risk became even more pronounced. Adolescents with medium cognitive function faced a 1.92 times higher risk, and those with low cognitive function had a 2.97 times higher risk of experiencing an ischemic stroke.
Ischemic strokes occur when a blood clot blocks or narrows an artery leading to the brain, causing a reduction in blood flow and oxygen to brain tissue. Hemorrhagic strokes, on the other hand, happen when a blood vessel in the brain ruptures, leading to bleeding in or around the brain.
Another significant finding was that the risk of ischemic stroke was particularly high for individuals who experienced their first stroke before the age of 40. Among these individuals, those with medium cognitive function had nearly double the risk, and those with low cognitive function had over three times the risk, compared to their high-functioning peers. This early-onset risk highlights the importance of cognitive function as a predictor of stroke at a younger age, a critical period when preventive measures could have a substantial impact.
The study also found a notable difference in baseline characteristics among the cognitive function groups. Adolescents with low cognitive function were more likely to be overweight or obese, less likely to have completed high school, and more likely to live in neighborhoods with lower socioeconomic status. These findings suggest that cognitive function in adolescence is intertwined with various social determinants of health, which could further influence stroke risk.
With this in mind, the researchers conducted sensitivity analyses to ensure the robustness of their findings. They found that the association between lower cognitive function and increased stroke risk remained consistent even when the sample was restricted to individuals with optimal health in adolescence or those with normal blood pressure.
Additionally, when the analysis was extended to stratify the data by BMI categories, the researchers observed that individuals with low cognitive function and high BMI had the highest risk of stroke. This subgroup exhibited a sixfold increase in stroke risk compared to those with high cognitive function and low-normal BMI.
Despite its comprehensive approach, the study had several limitations. First, it lacked data on stroke incidents that occurred before January 2014. Lifestyle factors such as smoking, alcohol consumption, and physical activity, which could influence stroke risk, were not available. Additionally, while the study accounted for high school completion, it did not have detailed data on higher education levels or income. The study also did not account for other cardiometabolic conditions, such as hypertension, which could mediate the relationship between cognitive function and stroke.
Future research should explore the underlying mechanisms linking low cognitive function to increased stroke risk. Additionally, studies should investigate the potential role of lifestyle factors and other cardiometabolic conditions in this relationship. Understanding these connections could lead to more effective prevention strategies and healthcare interventions for at-risk populations.
The study, “Cognitive function in adolescence and the risk of early-onset stroke,” was authored by Aya Bardugo, Cole D Bendor, Carmit Libruder, Miri Lutski, Inbar Zucker, Avishai M. Tsur, Estela Derazne, Gal Yaniv, Raquel C Gardner, Hertzel C Gerstein, Tali Cukierman-Yaffe, Yael Lebenthal, David Batty, David Tanne, Ariel Furer, and Arnon Afek.
Gilad Twig
