Professor Velandai Srikanth
When we talk about cardiovascular disease, we’re referring to major disease such as having strokes, or heart attacks, or having heart failure. Our research has clearly shown that people who have strokes, heart failure or heart attacks are at very high risk of dementia in the future. Strokes can directly destroy brain cells and hence reduce the capacity of the brain to withstand other insults that might occur in the brain later on, such as Alzheimer’s Disease. Now, while these major events are important in increasing the risk of dementia, it must be kept in mind that the risk factors that lead to these diseases are also important. So, by controlling risk factors such as high blood pressure, diabetes, cholesterol, maintaining activity, stopping smoking; these can all reduce the risk of major cardiovascular disease and, by that, reduce the risk of a future dementia.
Blood pressure tends to increase first as people reach middle age, so middle age is between 40 and 60 years of age. At this point in time, control of blood pressure is likely to reduce the risk of brain injury later on, so one advocates the careful monitoring and control of blood pressure during middle age. But as one gets older and gets a bit frailer so, for example, those in their late 70s or 80s might have difficulty walking, might have poor balance, can have a risk of falling; in such people we are a bit more careful about how aggressively we treat their blood pressure. As one gets even older, blood pressure drops and tends to go down to the lower side of things in some people. Hence at that age, it is quite important to maintain blood pressure at a reasonable level so they can actually function well, and such people we don’t tend to put on high doses of blood pressure reducing medication or even sometimes take them off blood pressure reducing medication.
The relationship between body weight and dementia is quite complicated. As people develop dementia in older age, they tend to lose weight because the brain is probably telling them not to eat much, in some fashion, and hence they lose not just body weight but muscle weight as well. So the risk or the association between body weight and dementia is different in older people compared with younger or middle aged people. In contrast, if you look at middle age, having greater levels of obesity is associated with the risk of dementia in the future. For example, people who have a very large waist circumference, what we call central adiposity, more fat around their hips, tend to have a higher risk of dementia. Such fat can be a source of chronic inflammation and this can affect blood vessel health and brain health directly. So treatment of adiposity or obesity in middle age should be quite aggressive, and can potentially reduce the risk of dementia in the future.
People with advanced dementia tend to lose weight. We don’t know exactly why this happens, but it is probably as a result of the hunger centre in their brains becoming different in the way it acts, so their appetite and their desire for food goes down and we can’t exactly work out, or haven’t been able to work out until now, how to offset this. Research is under way to try and understand what parts of the brain are signalling to stop hunger from happening in people with advanced dementia.
So in people who have already developed strokes or heart attacks, it is still not too late to make a difference to their risk of dementia in the future. We found in our studies that having one stroke by itself may not increase the risk of dementia too much, but having more than one stroke clearly increases the risk of dementia. So, in people who have had a stroke, it is important to do everything you can, with the help of your specialist, to try and have treatments in place that reduce the risk of a further stroke. Now this might mean having blood thinning medications, anti-coagulant medications such as Warfarin, blood pressure reducing medications, and controlling your diabetes. Apart from this, stopping smoking and increasing physical activity are also important. Again, if you haven’t developed major cardiovascular disease, but have risk factors such as high blood pressure and diabetes, it is still not too late to make a difference. In fact, the earlier we treat people before they develop cardiovascular disease, the better it is. So control of blood pressure during mid-life and early older life, control of diabetes, again stopping smoking, increasing your physical activity, reducing your weight, are all important things that need to be aggressively done during middle life.
It is very important to treat vascular risk factors to prevent major cardiovascular disease, and by that I mean preventing strokes and heart attacks. We know that preventing strokes reduces the risk of dementia, and we know that preventing heart attacks reduces the risk of heart failure, which is a risk factor for dementia.
There are a lot of studies currently under way trying to find out if reducing blood pressure or diabetes by themselves can reduce the risk of future dementia. The difficulty with planning studies of this nature is that they require very large numbers of people to participate in these studies, and a very long follow up to see if they do develop cognitive impairment or not. We need to wait for the results of these studies to come out before we can conclusively say which way the evidence goes.
The most important focus needs to be on identifying people who are at highest risk of dementia and trying to design studies to intervene in such people. For example, people with clusters of vascular risk factors such as diabetes and hypertension could be most at risk of dementia, and trying to develop medications, or other lifestyle interventions, in such people will provide the maximum benefit in future dementia reduction.