Well shit; I've been writing about this for years.
1. A documented 33% dementia chance post-stroke from an Australian study?   May 2012.
2. Then this study came out and seems to have a range from 17-66%. December 2013.
3. A 20% chance in this research.   July 2013.
If you have anything close to a decent doctor a protocol will already be in place to prevent this from occurring. 

Mind the Connection: Link Between Stroke and Dementia More Powerful Than We Think

Covert Strokes That Canadians Don't Even Recognize Are Increasing Their Risk of Dementia
OTTAWA, ON--(Marketwired - June 09, 2016) - The Heart and Stroke Foundation 2016 Stroke Report reveals an increasingly powerful relationship between stroke and dementia due in part to covert strokes Canadians don't realize are happening. Covert strokes occur five times more often than obvious strokes, and both are happening at a younger age, opening the door to more and earlier dementia, and sounding the alarm for an increased focus on prevention.
New data confirms a profound link between these two diseases of the brain. Having a stroke more than doubles the risk of developing dementia. Out of every 100 stroke patients without a past history of dementia, 16 are likely to develop dementia after their first or subsequent stroke. One in three Canadians will develop stroke, dementia, or both.
Stroke happens when blood stops flowing to parts of the brain, causing cells to die. Vascular cognitive impairment is also the result of blood vessel problems and results in a range of cognitive deficits, from relatively mild symptoms to vascular dementia. Both obvious clinical strokes and covert strokes -- the type that happens when a small vessel becomes permanently blocked but there is no immediate outward physical damage -- can lead to dementia.
"Stroke and dementia need to be studied together because in some ways they are one and the same," says Dr. Andrew Demchuk, Director, Calgary Stroke Program and Heart and Stroke Foundation spokesperson. "Stroke causes brain cells to die and this can precipitate dementia or worsen pre-existing dementia. There are different causes of dementia, and research now shows that stroke is a major contributor."
According to a poll* commissioned by the Heart and Stroke Foundation, Canadians' awareness of both stroke and dementia is low: Less than half of Canadians know what a stroke is and fewer than one-third understand what dementia is and recognize the symptoms.
Uncovering covert strokes
Age is a risk factor for both stroke and dementia and as the population ages the actual number of strokes will rise, along with the number of people with dementia. Evidence is also showing that both are increasingly happening to younger people. According to the most recent data from the Canadian Institute for Health Information (CIHI), 17 per cent of stroke patients were between the ages of 20 and 59. Similarly, according to new research that uses brain scan technology, covert strokes are also happening at an early age.
"About three per cent of Canadians in their 40s have evidence of a covert stroke. They can experience small strokes and they do not even realize it, and then it is too late as the damage is not reversible," says Dr. Eric Smith, Stroke Neurologist, Calgary Stroke Program and Heart and Stroke Foundation spokesperson.
Currently one in 10 Canadians over 65 has dementia, and this increases to three in 10 over the age of 85. According to our poll, more than one-quarter of Canadians mistakenly believe that dementia is a normal part of aging.
Dementia at an early age brings unique challenges, starting with difficulty getting a diagnosis, work-related and financial difficulties, as well as strain on relationships with spouses and children.
"My executive function and word-finding skills are damaged and this is permanent. I cannot multi-task the way I used to, and I have very little short-term memory so I have a white board in the kitchen and I write everything down. Everything also goes in my calendar. Thank goodness for technology; it is my lifeline." says Susan Robertson, who was a full-time working mother when she had a stroke at 36.
Prevention
Stroke -- either a first stroke, subsequent stroke, TIA (mini-stroke) or covert stroke -- can be prevented by managing vascular risk factors including high blood pressure and cholesterol and diabetes, as well as unhealthy behaviours such as tobacco use, physical inactivity and poor diet. The same is true for dementia. Dementia can be prevented, it can be delayed or its progression can be slowed by the same healthy behaviours. Physical activity and new learning -- for example, learning a language or musical instrument -- are particularly beneficial to good brain health.
Canadians' awareness of risk factors is poor:

• High blood pressure is the number one modifiable risk factor for stroke yet according to our poll, less than one-quarter know it is a risk factor at all.
• When asked to identify risk factors, just over one-quarter named smoking, one-third identified poor diet, and less than one-fifth noted physical inactivity.

It is never too early to prevent both stroke and dementia and it is never too late to reduce risk.
"Reducing stroke risk protects your brain. Healthy living is about dementia too. Everything you do to protect your body protects your brain," says Dr. Smith.
Once someone has had a stroke or TIA, their odds of having another increase. Secondary stroke prevention services help Canadians prevent a new stroke from happening after a first event. Evidence shows access to secondary prevention services reduces mortality by 25 per cent, and reduces the risk of having another stroke by between 50 and 80 percent. These services are delivered in dedicated clinics or through other types of services across the country.
The Heart and Stroke Foundation carried out an inventory of stroke prevention services across the country, revealing:

• Prevention services exist in every province including at least one in every urban health region.
• There are more clinics and better access in the big urban centres.
• More than 51,000 patients are seen each year.
• The majority of patients are referred from emergency departments or family doctors.
• Just over half of the clinics provide access to a CT scan within 48 hours.
• Only half of the clinics screen for cognitive impairment (including the severest form -- dementia) or depression or both.

Dr. Robert Côté, Director, Stroke Prevention Clinic, McGill University Health Centre, and Heart and Stroke Foundation spokesperson notes that weaknesses in the system stand in the way of some patients receiving the best care. The transition from assessment at the stroke prevention clinic to primary care (family doctor) is not always seamless and timely, and some patients do not have a primary care provider, or are not getting the support they need to manage their risk factors. Access to secondary prevention services are not consistent because of geography, limited hours of operation, and availability of stroke experts and diagnostic tests.
Knowing your risk factors
Nine in 10 Canadians have at least one risk factor for stroke and heart disease. This includes risk factors Canadians can do something about, and those they cannot change.
Risk factors Canadians can change:

• Know and control your blood pressure.
• Eat a healthy balanced diet that consists of a variety of natural/whole and minimally processed foods.
• Be physically active. Accumulate at least 150 minutes of moderate- to vigorous-intensity aerobic physical activity per week, in bouts of 10 minutes or more.
• Be smoke free.
• Manage diabetes.
• Limit alcohol. Women should limit themselves to no more than two drinks a day, to a weekly maximum of 10; and men to three drinks a day or a weekly maximum of 15.

Take the Heart&Stroke Risk Assessment at heartandstroke.ca/ehealth
Risk factors Canadians cannot change:

• having had a previous stroke or TIA (mini-stroke)
• family history of stroke or blood vessel problems
• age -- the older you are, the higher your risk of stroke
• sex -- until women reach menopause, they have a lower risk of stroke than men
• ethnicity -- people of African or South Asian descent are more likely to have high blood pressure and diabetes.
• people of Indigenous heritage are reported to have higher incidence of high blood pressure and diabetes.

Stroke and dementia statistics

• There are 62,000 strokes in Canada each year -- that is one stroke every nine minutes.
• 405,000 Canadians are living with the effects of stroke.
• Stroke is the third leading cause of death in Canada. Each year, over 13,000 Canadians die from stroke^.
• One in three Canadians will develop stroke, dementia, or both.
• Having a stroke more than doubles someone's risk of developing dementia.
• 10 per cent of stroke patients are diagnosed as having prior dementia, and an additional 10 per cent develop dementia after their first stroke. Having recurrent strokes further increases the chances of cognitive decline. More than one-third of patients develop dementia after a second stroke.
• About three per cent of Canadians in their 40s have evidence of a covert stroke and almost 20 per cent of 70-year-olds have experienced covert strokes.
• Currently one in 10 Canadians over 65 has dementia, and this increases to three in 10 over the age of 85.
• The number of people with vascular dementia doubles every five years after age 65.
• Combined direct (medical) and indirect (lost earnings) costs of dementia total $33 billion a year in Canada. If nothing changes, this number will climb to $293 billion a year by 2040.

Visit heartandstroke.ca/strokereport for the full report.
* The poll with Canadians was conducted by Environics Research Group by telephone with 3,100 respondents 18 years and older, February 3-14, 2016.
The Heart and Stroke Foundation's mission is to prevent disease, save lives and promote recovery. A volunteer-based health charity, we strive to tangibly improve the health of every Canadian family, every day. Healthy lives free of heart disease and stroke. Together we will make it happen. heartandstroke.ca