What is a ‘risk’?
A person's risk of developing a disease or condition is the chance that it will affect them over a certain period of time. We are all at some level of risk of developing dementia, but some of us have a higher or lower risk than others. For example, a typical 80-year-old woman is much more likely to develop dementia in the next five years than a typical 30-year-old woman.
What is a 'risk factor'?
A risk factor is anything that increases a person's risk of developing a condition. For dementia there are a mixture of factors - some that can be avoided and others that are impossible to control. However, having any of the risk factors does not mean a person will necessarily develop dementia in the future. Likewise, avoiding risk factors does not guarantee that a person will stay healthy, but it does make this more likely.
Many risk factors have been discovered from studying large groups of people and looking at what those with dementia have in common. However, just because something is linked to dementia does not mean that it causes the condition. The link may be the other way round, ie dementia increases a person's chances of having the apparent risk factor - for example, depression in later life. Or they may share an underlying cause.
Something is more likely to be a genuine risk factor if there is a plausible way in which it might make dementia more likely, based on our understanding of how dementia develops. A good example is the clear way that, because high blood pressure can cause strokes and strokes can cause vascular dementia, high blood pressure is a risk factor for vascular dementia.
Using clinical trials
Overall, the best kind of evidence for identifying risk factors comes from clinical trials. These look at what happens over time when some people in the trial are given a medicine (eg to lower blood pressure) or adopt different behaviours (eg various diets). Such dementia 'prevention' trials are increasing but are still not common. In order to show an effect on dementia, they generally need to run for many years and involve hundreds or even thousands of people. Even trials that assess smaller changes - for example, by testing mental abilities - can be very complicated to organise and expensive to do.
Very few studies of dementia risk factors have looked specifically at the less common dementias such as frontotemporal dementia (FTD) or dementia with Lewy bodies (DLB). These pages, unless stated otherwise, is about the risk factors for the more common types of dementia. These are Alzheimer's disease, vascular dementia and mixed dementia (when someone has more than one type of dementia, most often Alzheimer's disease and vascular dementia).
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