Dr Kevin McCarroll
Medical Matters
Last month saw the marking of World Alzheimer’s Day as part of an international campaign to raise awareness of a condition that is still stigmatised and often misunderstood. It is estimated that there are about 50 million people in the world with dementia and this figure continues to rise with an ageing population. In fact, a substantial proportion of new cases now occur in poor to middle income countries. The age at which dementia develops though is rising in the West as general health improves.
In truth, while we know what happens to the brain in dementia, we don’t really understand what triggers these changes. Indeed, it is now believed that several factors in midlife and even earlier influence our risk of developing dementia in older age. A review of the most up to date studies on dementia risk published in the Lancet this year identified up to 12 modifiable risk factors which might account for up to 40% of all cases of dementia globally.
But what are the main risk factors? High blood pressure in midlife has been associated in several studies with dementia in later life. For example, in one study of about 9000 adults aged between 50-60 a top blood pressure reading of 130 mmHg or more was associated with a 40% greater chance of dementia. Furthermore, in a pooled analyses of several large studies, more intensive blood pressure control lowered this risk by about 20%. Higher blood pressure causes hardening of the arteries in the brain and even from the age of 40 has been shown to predict smaller brain volume in later life.
Obesity appears to increase the risk of dementia by about 20%. Fat cells are metabolically active and produce inflammatory chemicals that can pass into the brain and may be a factor. Diabetes has also been clearly identified as a risk factor though despite this, studies of intensive blood sugar control have not reduced this risk. Exercise may help lower risk but the overall effect seems to be small.
Taking alcohol in excess is certainly not healthy for the brain and accelerates brain shrinkage. Consuming more than 21 units per week was associated with a 20% increased risk of dementia in later life. Smoking is also a clear risk factor but giving up can offset this risk. For example, among 50,000 males aged 60 or older, stopping smoking over four years reduced the risk of dementia in the following eight years by 10%.
Clustering of several cardiovascular risk factors in midlife also appears to synergistically increase the risk. While a Mediterranean diet has been advocated to help prevent cognitive decline, evidence remains inconsistent. In addition, studies of vitamin and other supplements have failed to show any effect.
Higher childhood education levels and lifelong higher educational attainment also appear to lower dementia risk. Cognitive ability improves with education up to late adolescence when the brain is most plastic but further gains after the age of 20 appear limited. However, mental activity in general might help to maintain cognitive function but studies are inconsistent with some however showing beneficial effects. Interestingly, in some large studies a lower age of retirement seems to be associated with worse subsequent performance of memory and language tests.
Social contact is another factor that has been linked to dementia incidence even after adjustment for socioeconomic and lifestyle factors. In a UK study of 10,308 people, frequent contacts at the age of 60 was associated with a lower dementia risk over 15 years of follow up. This might in part be explained by enhancement of cognitive reserve and encouraging beneficial behaviours.
What about sleep? Well, poor sleep affects cognitive function and has been linked to chronic inflammation and other changes in the brain. Studies suggest that sleep times of less than five hours may confer a greater risk of Alzheimer’s dementia. Depression later in life may also be a factor but there doesn’t seem to be a link when it occurs at a much younger age.
Finally, traumatic brain injury has long been identified as increasing the risk of Alzheimer’s in later life. More recently what’s been described as chronic traumatic brain encephalopathy acquired from sports injuries may also increase the risk of dementia though more research is underway.
So to summarise, what can you do to preserve your brain health and substantially lower your chance of vascular and Alzheimer’s dementia later in life? Well the available evidence supports aiming for a systolic blood pressure (top reading) of under 130 mmHg, cut down alcohol to less than 21 units week, avoid or stop smoking, reduce obesity, sustain midlife physical activity and avoid situations that might lead to head trauma!
What’s become clearer is that several factors earlier in life may cause brain changes that predispose to dementia, and that addressing these probably helps to stave off its later development.
Dr Kevin McCarroll is a Consultant Physician in Geriatric Medicine, St James’s Hospital, Dublin.