Declining Incidence of Stroke and Dementia: Coincidence or Prevention Opportunity?

Stroke and dementia pose significant threats to the adult brain and share the same treatable risk factors.¹ Stroke incidence in high-income countries has been declining,² coinciding with better risk-factor control. However, hitherto there have been encouraging trends, but no proof, of declining dementia incidence.³ To address this, we analyzed health care administrative data from the Canadian Institute for Health Information for the province of Ontario, Canada.

We obtained data from the Ontario Health Insurance Plan (OHIP), Ontario Drug Benefit (ODB) Database, Discharge Abstract Database (DAD), and the National Ambulatory Care Reporting System (NACRS). We used intercensal and postcensal projections based on census data from 2001, 2006, and 2011 to estimate the Ontario population. The OHIP physician billing database captures approximately 98% of all physician billings for the province of Ontario and includes diagnosis and procedure codes. The ODB database identifies prescription claims for medications covered under the provincial drug formulary for individuals aged older than 65 years. The DAD and NACRS databases contain diagnosis and procedure information for all hospital admissions and emergency department visits in Ontario. By law in Ontario, all hospital and emergency department admissions are included in these databases, so the sampling frame is population-based.

This prospective longitudinal population-based study was approved by the Sunnybrook Health Sciences Centre Research Ethics Board. Patient consent was waived because data collection for the registry is done without patient consent, as the Institute for Clinical Evaluative Sciences is named as a prescribed entity under provincial privacy legislation.

We identified strokes in DAD and NACRS using International Statistical Classification of Diseases and Related Health Problems, Tenth Revision codes I60, I61, I63, and I64 and OHIP codes 430, 431, 434, and 436. We defined acute stroke as 1 hospitalization (DAD) or 1 emergency department visit (NACRS) with a most responsible diagnosis of stroke, or 2 OHIP claims for physician visits with a diagnosis of stroke within the 365-day calendar year. We used International Classification of Diseases, Ninth Revision (290, 294, 331, and 797) and International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (F00-F03, F05, F06, F09, G30, G31, and R54) codes from DAD, NACRS, and OHIP, as well as ODB claims for cholinesterase inhibitors. We defined dementia as 1 hospitalization (DAD) with any field diagnosis of dementia, 1 physician visit with diagnosis of dementia (OHIP), or 1 prescription for cholinesterase inhibitor (ODB) within the previous year.

We included patients aged 20 years or older, diagnosed as having stroke between April 1, 2002, and March 31, 2014. We excluded patients with invalid health card numbers, missing age/sex, and nonresidents of Ontario. We established a look-back window of 7 years (1995-2001) to exclude cases diagnosed before the study period. As a result, any case identified between April 1, 1995, and March 31, 2002, was not counted, and for each given fiscal year, the individuals with prevalent dementia were also removed from the denominator. Cases with multiple strokes or multiple dementia codes over the study period contributed only once. We calculated stroke and dementia age- and sex-standardized incident rates per 1000 inhabitants for each fiscal year between 2002 and 2013 (12 years).

Between 2002 and 2013, age- and sex-standardized stroke and dementia incidence rates in the Ontario population decreased by 32.4% (P < .001) and 7.4% (P = .009), respectively (Table and Figure).

To our knowledge, this is the first study showing a decline in dementia incidence over time. This report may also be unique in showing a corresponding decline in stroke incidence in the same population. Previous evidence suggests that diet, exercise, cognitive training, and vascular risk monitoring may improve or maintain cognitive functioning in at-risk elderly people.⁴ Hence, primary prevention strategies resulting in improved risk-factor control may have concurrently reduced dementia risk.⁵ In addition, given that cerebrovascular disease is an important cause of dementia and that 60 to 80% of all major dementias have a vascular component, the falling incidence of stroke may have further contributed to the decline in dementia incidence.⁶

Corresponding Author: Vladimir Hachinski, CM, MD, FRCPC, DSc, London Health Sciences Centre, University Hospital, 339 Windermere Rd, London, ON N6A 5A5, Canada (vladimir.hachinski@lhsc.on.ca).

Author Contributions: Dr Hachinski had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study concept and design: Sposato, Hackam, Hachinski.

Acquisition, analysis, or interpretation of data: Sposato, Kapral, Fang, Gill, Hackam, Cipriano.

Drafting of the manuscript: Sposato, Hachinski.

Critical revision of the manuscript for important intellectual content: All authors.

Statistical analysis: Fang.

Administrative, technical, or material support: Kapral, Gill, Hackam, Cipriano.

Study supervision: Hachinski.

Conflict of Interest Disclosures: None reported.

Funding/Support: This study was funded by the Premier’s Discovery Award in the Life Sciences and Medicine, Intergovernmental Committee for Economic and Labour Force Development, Toronto, Ontario, Canada, held by Dr Hachinski. The Institute for Clinical Evaluative Sciences (ICES) is supported by an operating grant from the Ontario Ministry of Health and Long-Term Care (MOHLTC). Dr Kapral is supported by a career investigator award from the Heart and Stroke Foundation, Ontario Provincial Office, Canada.

Role of the Funder/Sponsor: The funding agencies had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Disclaimer: The opinions, results, and conclusions are those of the authors and are independent from the funding sources. No endorsement by the ICES or the Ontario MOHLTC is intended or should be inferred.

Additional Contributions: We gratefully acknowledge the contribution of Jianbao Wu, PhD (Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada), for statistical analyses. He did not receive compensation for his contribution.