Along with cardiovascular disease, cancer and metabolic diseases, neurodegenerative diseases are responsible for 80% of deaths in non-smokers over the age of 50. Alzheimer’s disease (AD) is, by far, the most common neurodegenerative disease and the most common cause of dementia. Dementia is an overall term used to describe a particular group of symptoms which includes difficulties with language, memory, problem-solving - depending on which parts of the brain are affected. AD is a progressive brain disease in which the nerve cells (or neurones) are damaged. The rate of progression and abilities affected will vary between individuals, however the condition is ultimately fatal as basic bodily functions are eventually affected.
Although Alzheimer’s was discovered well over a century ago, the exact causes of this life altering disease are not yet fully understood. Additionally, despite the huge impact it has, no cure has yet been developed and currently treatments are primarily aimed at treating symptoms, though some recently developed drugs are disease modifying and slow down the progression of early AD by treating the cause. Aducanumab, Lecanemab and Donanedab target and remove beta-amyloid from the brain however they only serve to slow cognitive decline in individuals with early AD, not reverse changes in the brain.
The pathological hallmarks of Alzheimer’s disease are:
the accumulation of a plaques of protein called beta-amyloid outside neurones;
the accumulation of an abnormal form of tau protein within neurones;
followed by the damage and destruction of neurones.
One of the major challenges with AD is that symptoms become apparent approximately 20 years after brain changes start occurring. Therefore by the time a patient has symptoms of dementia the changes in the brain are irreversible.
The decades of disease development prior to the onset of symptoms is the ideal window for intervention to slow the progression of the disease. Improving the early detection of dementia at the preclinical stage is one of the most important challenges currently. MRI of the brain with volumetric measurement (measuring volumes of different parts of the brain for example the hippocampus) is able to predict who is likely to progress to AD when patients have mild cognitive impairment. We can also measure eye movements of patients using specialised cameras to measure brain health and predict which patients will progress to develop AD.
What are the causes of Alzheimer’s disease? Like other chronic diseases AD develops as a result of multiple factors rather than a single cause. Although some of these risk factors - age, genetics, family history and gender - cannot be changed, a significant number of cases are of AD can be prevented with a change in lifestyle factors. Older age is the greatest risk factor - the percentage of the population with Alzheimer’s disease increases dramatically every decade after the age of 65. It is, however, important to point out that AD is not a normal part of ageing - not all people who age will develop AD. It also tends to occur with greater frequency in females.
Over 99% of cases occur sporadically usually after the age of 65 whilst the remaining 1% of cases are due to the genetic form of the disease which is caused by rare variants of specific genes. There have been numerous genes identified which increase the risk of developing Alzheimer’s. One gene which is known to have a particularly strong impact is known as APOE. Everyone has one of three forms of this gene - APOE-e2; APOE - e3; APOE-e4 - which are inherited from each parent. Having the e4 variant increases (but does not guarantee) your risk of developing the disease. Risk is tripled in the case of inheriting one e4 and eight to twelve times higher if two are inherited. On the other hand, the e2 form seems to reduce risk. It is possible to test for these gene variants, if you are interested in this you can speak to your longevity medicine specialist.
What can doctors and patients do to prevent or reduce the chances of developing Alzheimer’s disease? Eating a high-quality diet, regular engagement in cognitive activities, regular physical activity, light to moderate alcohol intake, and not smoking are associated with a 60 % decrease in developing Alzheimer’s disease.
Having good cardiovascular health is essential for brain health. In fact many factors which increase cardiovascular disease are also known to increase the risk of dementia. These include having high blood pressure, diabetes, obesity and elevated cholesterol levels. This is because a healthy heart and vascular system ensures sufficient blood, and therefore oxygen and fuel supply, to the brain.
Other lifestyle factors which influence risk:
having a nutritious diet - having a heart healthy diet reduces your risk of developing dementia. This includes a diet rich in fruit, vegetables, wholegrain, fish, chicken, nuts, legumes and healthy fats with limited amounts of saturated fat, red meat and sugar. Consumption of foods rich in omega-3 fatty acids (particularly fatty fish) is especially important;
being physically active throughout life reduces risk of dementia;
having quality social and cognitive engagement supports good brain health;
consistently getting good amounts of quality sleep activates your glymphatic system to clear out toxins from your brain;
smoking and excessive alcohol consumption increase cognitive impairment;
having a high level of education and/or learning new things builds your cognitive reserve which is your brain’s ability to make flexible and efficient use of cognitive networks despite any brain changes;
managing your stress and practicing good dental hygiene helps reduce chronic inflammation and therefore damage to your brain cells;
traumatic brain injury increases your risk of dementia (for example contact sports or heading a football);
high levels of exposure to certain environmental toxins, particularly air pollutants such as fuel fumes, increase dementia incidence.
Neurodegenerative diseases such as Alzheimer’s have a huge impact on the lives of patients and their caretakers and a significant impact on healthspan. While the exact causes of Alzheimer’s is still unknown and we still have no curative treatment, our priority needs to be in warding off our risk of this debilitating and fatal disease. Eating a high-quality diet, regular engagement in cognitive activities, regular physical activity, light to moderate alcohol intake, and not smoking are associated with a 60 % decrease in developing Alzheimer’s disease.
The healthy lifestyle habits to do so have been best summarised in the SHIELD plan developed by Prof. Rudolph E. Tanzi:
Sleep get 7 - 8 hours
Handling of stress
Interaction with friends
Learning new things
If you would like to test your personal risk factors for developing chronic diseases of ageing, find out more about the Longevity Annual health check and download the longevity doctor guide to healthy living.