Stroke is the third highest cause of death in Canada and is the second highest cause of death worldwide.
What is stroke?
A stroke is brain cell damage caused when blood stops flowing to the brain. If blood flow returns before brain cell damage happens, this is called a transient ischemic attack (TIA).
Many factors add to a person's stroke risk. Some, like ancestry, can't be changed. Others, like diet and exercise, can.
Does this mean that your lifetime risk of stroke is fixed if you have characteristics you can't change?
This is a question investigators wanted to answer in a population health study from the August 2022 issue of the Journal of the American Heart Association.
How did they conduct the study?
The investigators turned to an existing U.S. database from one of the largest and longest-running heart health studies in the world.
They identified middle-aged adults who met three conditions:
had never had a previous stroke or TIA
had genetic testing results
had been evaluated for a heart-healthy lifestyle using the American Heart Association Life's Simple 7, which included total cholesterol, blood pressure, blood sugar, physical activity, diet, smoking status, and body mass index.
They grouped people by low, intermediate, and high genetic stroke risk using a research tool called the polygenic risk score (PRS). They then measured the effect of low and high heart health on stroke risk.
Looking at the social construct of race, they saw this tool had only been used in people who identified as White. They wanted to learn if this tool was equally effective at predicting the genetic risk of stroke in groups with more diverse ancestry.
They ended up following over 11 500 people for over 19 years to capture their lifetime stroke risk. Over half of the study participants were women (56%). Almost a quarter identified as Black and just over three-quarters identified as White.
Using statistical models, they compared the effects of genetics and/or heart health on lifetime stroke risk.
What did they find?
The investigators found:
the best heart health lifestyle was tied to a lower lifetime risk of stroke at all levels of genetic risk, regardless of ancestry
no proof that genetics and heart health multiplied instead of added to each other’s stroke risk
using the PRS to predict if people identifying as Black would have a stroke was no better than just using their heart health scores.
Can we apply the study findings directly to Canadians?
Perhaps the reason the tool did not work as well at predicting stroke in Black people was due to differences in social and environmental exposure. Social and environmental changes affect how certain genes are expressed. The study of how this happens is called epigenetics.
In Canada, of the 3.5% of people identifying as having Black ancestry, it's unclear whether they would have had the same social and environmental exposures as the people participating in the study. People who identify as First Nations or South Asian in Canada are also at greater risk for stroke. Because this study did not include these groups, we cannot predict to what degree they might benefit from a heart healthy lifestyle.
Access to public and preventive healthcare is also different in our two countries. If people saw their family doctors regularly, it would make sense that their heart health would change over time. However, heart health was only recorded at the time participants entered the study and so would not have accounted for this.
Since this study, the stroke risk factors have been updated and checking these at enrolment as well as at the time of stroke would make their relationship with genetic factors clearer. But before that can happen, investigators need a better tool to predict genetic stroke risk.
What Canadians can take away from this research is that if life deals them an above-average stroke risk, choosing a heart-healthy lifestyle may help - how much will need to be learned from future studies.
References:
Canadian Institute for Health Information. Improved stroke data means better care and outcomes for patients. Canadian Institute for Health Information. June 15, 2021. Accessed August 31, 2022. https://www.cihi.ca/en/improved-stroke-data-means-better-care-and-outcomes-for-patients#:~:text=Stroke%20is%20the%20third%20leading,62%2C000%20strokes%20occur%20each%20year
Singh PK. World stroke day. World Health Organization. October 28, 2021. Accessed August 31, 2022. https://www.who.int/southeastasia/news/detail/28-10-2021-world-stroke-day
Heart and Stroke Foundation of Canada. What is stroke? Heart & Stroke. Accessed August 31, 2022. https://www.heartandstroke.ca/stroke/what-is-stroke
Thomas EA, Enduru N, Tin A, et al. Polygenic risk, midlife Life's Simple 7, and lifetime risk of stroke. J Am Heart Assoc. 2022;11:e025703. doi.org/10.1161/JAHA.122.025703
Collaborative Studies Coordinating Center University of North Carolina at Chapel Hill. ARIC: Research with Heart since 1987. Accessed August 31, 2022. https://sites.cscc.unc.edu/aric/
Chou V. How science and genetics are reshaping the race debate of the 21st century. SITNBoston. April 17, 2017. Accessed September 2, 2022. https://sitn.hms.harvard.edu/flash/2017/science-genetics-reshaping-race-debate-21st-century/
Markus HS, Khan U, Burns J, et al. Differences in stroke subtypes between Black and White patients with stroke. Circulation. 2007;116:2157–2164. doi.org/10.1161/CIRCULATIONAHA.107.699785
Kuzawa CW, Sweet E. Epigenetics and the embodiment of race: developmental origins of US racial disparities in cardiovascular health. Am J Hum Biol. 2009;21:2-15. doi:10.1002/ajhb.20822
Statistics Canada. Black History Month 2022... by the numbers. Statistics Canada. February 1, 2022. Accessed Sep 2, 2022. https://www.statcan.gc.ca/en/dai/smr08/2022/smr08_259
Heart and Stroke Foundation of Canada. Taking control. Heart & Stroke. Accessed September 2, 2022. https://www.heartandstroke.ca/-/media/pdf-files/canada/other/aboriginal_takingcontrol.ashx#:~:text=Why%20are%20Aboriginal%20People%20at%20a%20greater%20risk%3F&text=All%20of%20these%20factors%20increase,that%20of%20the%20general%20population
Chiu M, Austin PC, Manuel DG, Tu JV. Comparison of cardiovascular risk profiles among ethnic groups using population health surveys between 1996 and 2007. CMAJ. 2010;182:E301-E310. doi.org/10.1503/cmaj.091676
Lloyd-Jones DM, Allen NB, Anderson CAM, et al. Life’s Essential 8: updating and enhancing the American Heart Association’s construct of cardiovascular health: a presidential advisory from the American Heart Association. Circulation. 2022;146:e18–e43. doi.org/10.1161/CIR.0000000000001078
Comments