Causes, Genetic Factors, and Risk Factors of Alzheimer's Disease

Alzheimer's disease is a progressive neurological (brain) disorder that leads to the loss of cognitive functions such as memory, thinking, and reasoning. The cause of the disease remains unclear, but there are some theoretical explanations and related risk factors. These complex brain changes may start several years or even decades before any symptoms appear. Researchers believe that genetic factors combined with lifestyle and environmental factors contribute to the development of the disease.

Alzheimer's disease causes extensive damage and loss of brain cells (neurons) and their connections (synapses). This damage begins in the brain regions that control memory. As the damage spreads throughout the brain, more cognitive and physical abilities are affected, resulting in physical atrophy of the brain. There are two main hypotheses regarding the development of Alzheimer's disease:

This is the earliest theory used to explain Alzheimer's disease. Cholinergic neurons in the brain play a crucial role in cognition (including learning and understanding). In patients with Alzheimer's disease, cholinergic neurons are severely damaged. Additionally, a theoretical cause of the disease is the lack of a messenger chemical substance called acetylcholine (ACh) in the brain. Acetylcholine plays a significant role in brain functions such as learning and memory. The only currently approved drugs for Alzheimer's disease help maintain the level of acetylcholine in the brain. These drugs can temporarily slow down cognitive symptoms, but they cannot prevent long - term brain damage.

For many years, researchers have believed that an abnormally high level of beta - amyloid (a protein that wraps around nerve cells) can form amyloid plaques in the brain. These plaques are considered one of the causes of cognitive decline in Alzheimer's disease. This hypothesis is based on an influential research paper published in 2006. However, attempts to treat beta - amyloid with drugs have not improved the symptoms of Alzheimer's disease. Moreover, researchers have found that amyloid plaques also appear in the bodies of people without Alzheimer's disease as they age. There was once a report that questioned this hypothesis because a neuroscientist found that the images in the 2006 study had been tampered with. Since then, researchers have been cautious about the beta - amyloid hypothesis. However, the results of clinical trials of a drug called Leqembi (lecanemab) have once again confirmed the role of beta - amyloid in the development of Alzheimer's disease. Lecanemab reduces the amount of amyloid in the brains of participants, leading to a moderate improvement in symptoms after 18 months. Nevertheless, more research and trials are needed to confirm this controversial hypothesis. Meanwhile, researchers are also looking for new explanations for neuron loss.

Some cases of early - onset Alzheimer's disease are familial, meaning that children may inherit certain mutations from their parents. In these cases, gene mutations can cause the disease. If there is a history of early - onset Alzheimer's disease in your family, consider discussing genetic testing with your healthcare provider. About 70% of Alzheimer's disease cases are related to genetic factors. The genetic mechanism of late - onset Alzheimer's disease is still unclear, and this disease does not seem to be hereditary within families. The gene that has the greatest impact on the risk of late - onset Alzheimer's disease is apolipoprotein E (APOE). Everyone has some form of APOE (or variant) in their DNA. If you inherit the ɛ4 variant, you are more likely to develop the disease. On the other hand, having the relatively rare APOE ε2 variant can actually help you prevent Alzheimer's disease.

Age is the most important risk factor. Most symptoms of Alzheimer's disease start to appear after the age of 65, and the proportion of people with the disease increases with age. 40% of people over the age of 85 have Alzheimer's disease.

Nearly two - thirds of Alzheimer's disease patients are people designated as female at birth. However, the risk of women developing the disease may not necessarily be higher. For example, this difference may be because women have a longer average lifespan than men. In the United States, the proportion of men and women with Alzheimer's disease is the same in each age group. Other studies have also revealed gender and gender - bias issues in research on the elderly.

Alzheimer's disease is common among Black and Hispanic populations. However, when socioeconomic factors and health conditions are considered, the risk differences disappear.

These include hypertension, heart disease, and stroke. Vascular problems (for example, due to heart failure) can affect the blood supply to the brain, thereby causing brain inflammation and eventually leading to Alzheimer's disease.

These include type 2 diabetes, high LDL cholesterol, and obesity. High LDL cholesterol levels and obesity in middle age can increase the risk of developing Alzheimer's disease.

Depression increases the risk of developing the disease. Antidepressant treatment may reduce this risk, but there is currently insufficient research to confirm this. Depression may also be an early sign of Alzheimer's disease because dementia can also cause similar emotional symptoms.

Social isolation refers to a lack of social interaction. Loneliness is different - it is the feeling of being alone or isolated from the world, and this can happen even when there are people around. Both are risk factors for Alzheimer's disease. Re - engaging in social activities can help protect you. Talking to others or participating in volunteer activities can improve your mood, cognitive abilities, and overall well - being.

Traumatic brain injury refers to a blow or shock to the head. A history of traumatic brain injury increases the risk of developing Alzheimer's disease. This is especially true for severe injuries, but even minor traumatic brain injuries (such as concussions) can have long - term effects.

Heavy alcohol consumption is associated with brain changes and cognitive decline, although there is not enough evidence to suggest that it causes these problems. This does not mean that you must completely abstain from alcohol - research shows that light to moderate alcohol consumption from middle to late age can reduce the risk of cognitive decline and dementia.

People who have never smoked or have quit smoking for a long time have a lower risk of developing Alzheimer's disease. Even if you do not completely quit smoking, reducing your smoking habit can still reduce the risk. Second - hand smoke can also increase the risk of developing the disease, especially when you are exposed to it at home.

Alzheimer's disease is associated with hearing loss. Researchers are not clear about the cause - and - effect relationship between the two. One main hypothesis is that hearing impairment may lead to social isolation, which is a risk factor for Alzheimer's disease. Another hypothesis is that people with hearing loss need more cognitive resources to process sound, leaving fewer resources for other cognitive functions.

Higher levels of fine particulate matter (PM2.5, pollution from sources such as power plants, construction sites, and fires) are associated with a higher incidence of Alzheimer's disease. Other types of pollution, such as nitrogen oxides (emitted by cars and power plants during fuel combustion) and sulfur dioxide (emitted by industrial facilities during fossil fuel combustion), can also cause brain damage similar to that in patients with Alzheimer's disease.

Regular physical activity can reduce the risk of developing Alzheimer's disease and all other types of dementia. A long - term follow - up study found that physical activity helps prevent Alzheimer's disease in the long run.

Just like physical activity, keeping your mind active (especially before the age of 20) helps prevent Alzheimer's disease. Research shows that higher education, reading, speaking a second language, playing music, and other cognitive - stimulating activities, as well as having a mentally challenging job, can reduce the risk of dementia.

Alzheimer's disease leads to the loss of cognitive functions and is common in people aged 65 and above. Although the pathogenesis of the disease is unknown, it is likely the result of the combined action of genetic and environmental factors. Age is the greatest risk factor, and other known risks include heart disease, brain injury, and insufficient mental or physical activity. Currently, research has begun to cover more diverse populations to better understand who is prone to the disease, but it is still impossible to accurately predict who will develop the disease.