Education and Stroke – Causal Relationship or Chance?

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A stroke happens when the blood supply to part of your brain is cut off, which can cause your brain cells to become damaged or die. It is a medical emergency and requires urgent treatment. The two main types of stroke are ischaemic, which is due to a lack of blood flow, and haemorrhagic, which is due to bleeding.  Strokes are serious and the second leading cause of death and disability globally. In Europe alone, over 1.5 million people suffer a stroke annually, and this medical condition had emerged as a significant public health priority in the whole world in recent decades.

Evidence shows that there are many traditional factors associated with increased stroke risk. The ten top modifiable risk factors for stroke were hypertension, lack of physical activity, abnormal lipids, unhealthy diet, abdominal obesity, psychological factors, current smoking, cardiac causes, alcohol consumption, and diabetes. Together, these ten risk factors accounted for almost 90% of stroke risk. However, there is growing evidence supporting that low education levels are also linked to increased stroke risk. But it is unclear whether there is a causal relationship between education and risk of stroke. In order to shed more light on this, some researchers conducted a study using specific methods and analyses to assess whether there is a causal relationship between education and risk of different types of strokes, including total stroke, ischaemic stroke, and haemorrhagic stroke.

Image 1: Ischaemic stroke and haemorrhagic stroke.

The scientists involved conducted a large-scale, population-based prospective cohort study without pre-existing stroke, meaning that the study conducted lasted over a long period of time (median follow-up of 25.3 years) and used a substantial number of participants (11,509 participants) who were random individuals from the population (in order to be representative of the population), ensuring that the participants had never had a stroke before. Education of the participants was self-reported at the beginning of the study as the highest qualification completed in school. There were three categories used which included basic education (less than college/sixth form completion), intermediate education (completion of sixth from, college degree or vocational school), and advanced education (attending or completed university).

During the median follow-up of 25.3 years, 915 cases (8%) of stroke occurred. Since total stroke was divided into its two main kinds, ischaemic and haemorrhagic, and their mechanisms are quite different, the researchers expected that education might have different effects on these two types of strokes. As mentioned before, they were also questioning whether there was a causal relationship between education and risk of total stroke and its subtypes. The results of the study showed that participants with an advanced education level were associated with 25% decrease in the rate of incident stroke, whereas those with basic education had the highest risk of incident ischaemic stroke and haemorrhagic stroke.

In their analysis of education and total stroke, the researchers did not detect a causal relationship between them. When education and haemorrhagic stroke was analysed, the researchers did not find a causal relationship between them either. However, when education and ischaemic stroke was analysed, the researchers observed evidence that education was likely a negative causal risk factor for ischemic stroke.

Image 2: Cumulative curve for incident total stroke and the 3 varying education levels, during the median follow-up of 25.3 years.

The protective role of educational achievement on cardiovascular disease (eg. stroke) had been described in previous studies, and so the explanation for why education level protected against stroke might relate to the broad benefits of education as explained in these previous studies. Higher educational attainment is associated with a healthier lifestyle, a job with safe working conditions, and better access to healthcare. Those with higher education are more likely to stay away from major cardiovascular disease risk factors such as smoking and over-consumption of alcohol, and are generally made aware of their damaging effects on health. Yet the study in question did not find any causal relationship between education and total stroke or haemorrhagic stroke, whilst education was likely a negative causal risk factor for ischaemic stroke.

The researchers analysed that it might be explained that stroke was a diverse collection of clinically related but different disorders, meaning that its different subtypes had distinct underlying pathologies. Consider the serum lipid, for example, which is the amount of lipids (a type of fat) found circulating in your blood. There were opposite relationships with the serum lipids found in ischaemic and haemorrhagic strokes. In addition, high levels of total cholesterol and LDL cholesterol (also known as bad cholesterol) were both associated with an increased risk of ischaemic stroke, whereas low levels were associated with an increased risk of haemorrhagic stroke. Ischaemic stroke represents 70-90% of all strokes and, as shown by the study, a higher level of education brings a lot of other benefits besides a lower rate of ischaemic stroke.

In summary, the study supported that participants with higher educational attainments were associated with a decreased rate of total stroke and ischaemic stroke incident, but not haemorrhagic stroke incident. The researchers were also able to corroborate the protective role of education on stroke, and so, the critical importance of education should be reflected in public health, educational policy and governmental decision-making for many disease preventions.

Original Sources:
1. Xiuyun W, Qian W, Minjun X, Weidong L, and Lizhen L. (2020) “Education and stroke: evidence from epidemiology and Mendelian randomization study.” Scientific Reports. https://doi.org/10.1038/s41598-020-78248-8

2. Gill D, Efstathiadou A, Cawood K, Tzoulaki I, and Dehghan A. (2019) “Education protects against coronary heart disease and stroke independently of cognitive function: evidence from Mendelian randomization.” International Journal of Epidemiology. https://doi.org/10.1093/ije/dyz200

Image 1 Source:
https://healthjade.com/ischemic-stroke/

Image 2 Source:
Scientific Reports. “Education and stroke: evidence from epidemiology and Mendelian randomization study.” https://www.nature.com/articles/s41598-020-78248-8#citeas

Featured Image Source:
WealthManagementCanada.com “Behavioural Finance: The biases affecting decision-making in investing.” https://wealthmanagementcanada.com/blog/behavioural-finance-the-biases-affecting-decision-making-in-investing/

Edited by Cyrus Rohani-Shukla

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