Although there’s still no cure, researchers are continuing to develop a better understanding of what increases a person’s risk of developing Alzheimer’s disease. Here, Dr Mark Dallas outlines the ten risk factors that a review of 396 studies has highlighted as increasing the likelihood of developing the disease.
1. Education level
A lower education level is associated with an increased risk of Alzheimer’s disease. Previous evidence shows the longer you spend in education, the lower your risk of developing dementia. Research looking at the brains of people from different educational backgrounds also showed that people who were more educated had heavier brains. As you lose one third of your brain weight because of dementia, a heavier brain may make you more resilient.
2. Cognitive activity
Evidence shows that keeping our brains active can also fight against dementia. Activities such as word puzzles stimulate your brain and can strengthen connectivity between brain cells. This connectivity is broken down in dementia.
This latest study shows that we need to continue keeping our brains active, even in older age. Other studies agree that challenging our brains does indeed reduce our chances of developing dementia.
3. Hypertension in mid-life
Healthy hearts have long been linked to a healthy brain. Here, the current study indicates that high blood pressure (hypertension) in middle age increases Alzheimer’s risk.
Higher incidence of heart disease in those suffering from high blood pressure impacts on the blood and nutrient supply to the brain. Interestingly, this association still exists even for those who have high blood pressure on its own. The bottom line is that reduced blood supply to the brain is linked with Alzheimer’s.
4. Orthostatic hypotension
The study also highlighted orthostatic hypotension as a risk factor. This is when someone experiences low blood pressure when standing after sitting or lying down.
Because the body is unable to maintain sufficient blood supply to the brain during posture changes, this can have a long-term debilitating influence on brain activity, as a result of lack of oxygen to the brain, which increases risk of dementia.
The study found diabetes was associated with higher incidence of Alzheimer’s. As diabetes makes our body unable to properly regulate insulin, this changes both the way our brain cells communicate and our memory function – both of which are disrupted in Alzheimer’s disease.
Insulin is essential, as it regulates the metabolism of carbohydrates, fats and protein by helping blood glucose absorb into the liver, fat and muscles. Alzheimer’s disease appears to disrupts the brain’s ability to react to insulin.
A higher body mass index (BMI) in under 65s is linked to increased risk of dementia. The study suggests a body mass index between 18.5 and 24.9 for those under 65 – a healthy weight, in other words – may lower dementia risk. However, being underweight in middle age and later life can increase dementia risk.
It’s thought that a mixture of genetics, cardiovascular diseases and inflammation all contribute to this association between BMI and dementia.
7. Head trauma
However, it’s uncertain whether single or repetitive head trauma is the contributing factor. It’s clear that brain damage from head trauma is similar to that of dementia. This makes people more susceptible to further damage later from dementia.
High levels of the chemical homocysteine are a risk factor. Homocysteine is a naturally occurring amino acid involved in the production of our body’s defence mechanisms, including antioxidants that prevent cellular damage.
Animal studies suggest elevated levels of homocysteine damage brain cells by interfering with their energy production. Consuming more folate and vitamin B12 can lower homocysteine levels – and may reduce dementia risk.
Those living with Alzheimer’s also often suffer from depression, though it’s uncertain if depression causes Alzheimer’s or is just a symptom of the disease. However, a wealth of evidence supports that depression is indeed a risk factor, as this latest study has found. Research has even indicated a link between the number of depressive episodes – especially ten years prior to dementia onset – and higher risk.
Depression increases levels of harmful chemicals in our brain. An imbalance in these chemicals can lead to loss of brain cells. This, coupled with the loss of brain cells in dementia, increases likelihood of Alzheimer’s.
Lastly, stress was identified as a risk factor. Long term stress targets our body’s immune cells, which are important in keeping dementia at bay. In particular, the hormone cortisol is shown to contribute to stress and can impact on memory. Aiming to reduce stress and cortisol levels can therefore reduce the chances of developing dementia.
This study offers a complex picture of how we can combat the onset of Alzheimer’s – as well as ten areas that scientists need to concentrate on researching in the future. Though the findings may seem bleak, there is some promise in that many of these risk factors can be managed or modified through lifestyle changes, including diet and exercise.
Mark Dallas Associate Professor in Cellular Neuroscience, University of Reading
This article was first published in The Conversation on 22 July 2020.