Alzheimer’s causes

Still, scientists don’t yet fully understand what causes Alzheimer’s disease in most people. In people with early-onset Alzheimer’s, a genetic mutation may be the cause. Late-onset Alzheimer’s arises from a complex series of brain changes that may occur over decades. The causes probably include a combination of genetic, environmental, and lifestyle factors. The importance of any one of these factors in increasing or decreasing the risk of developing Alzheimer’s may differ from person to person.
One of the great mysteries of Alzheimer’s disease is why it largely affects older adults.
The greatest known risk factor for Alzheimer’s and other dementias is increasing age, but these disorders are not a normal part of aging. While age increases risk, it is not a direct cause of Alzheimer’s.

Most individuals with the disease are 65 and older. After age 65, the risk of Alzheimer’s doubles every five years. After age 85, the risk reaches nearly one-third

Another strong risk factor is family history. Those who have a parent, brother or sister with Alzheimer’s are more likely to develop the disease. The risk increases if more than one family member has the illness. When diseases tend to run in families, either heredity (genetics), environmental factors, or both, may play a role.

Health, environmental, and lifestyle factors
Research suggests that a host of factors beyond genetics may play a role in the development and course of Alzheimer’s. There is a great deal of interest, for example, in the relationship between cognitive decline and vascular conditions such as heart disease, stroke, and high blood pressure, as well as conditions such as diabetes and obesity. Ongoing research will help us understand whether and how reducing risk factors for these conditions may also reduce the risk of Alzheimer’s.

A nutritious diet, physical activity, social engagement, and mentally stimulating pursuits have all been associated with helping people stay healthy as they age. These factors might also help reduce the risk of cognitive decline and Alzheimer’s. Researchers are testing some of these possibilities in clinical trials.
Research is beginning to reveal clues about other risk factors we may be able to influence through general lifestyle and wellness choices and effective management of other health conditions.
Head injury: There is a link between head injury and future risk of dementia. Protect your brain by buckling your seat belt, wearing your helmet when participating in sports, and “fall-proofing” your home. Learn more about traumatic brain injury.
Heart-head connection: Some of the strongest evidence links brain health to heart health. This connection makes sense, because the brain is nourished by one of the body’s richest networks of blood vessels, and the heart is responsible for pumping blood through these blood vessels to the brain.

The risk of developing Alzheimer’s or vascular dementia appears to be increased by many conditions that damage the heart and blood vessels. These include heart disease, diabetes, stroke, high blood pressure and high cholesterol. Work with your doctor to monitor your heart health and treat any problems that arise.

Studies of donated brain tissue provide additional evidence for the heart-head connection. These studies suggest that plaques and tangles are more likely to cause Alzheimer’s symptoms if strokes or damage to the brain’s blood vessels are also present.

Overall healthy aging: One promising line of research suggests that strategies for overall healthy aging may help keep the brain healthy and may even reduce the risk of developing Alzheimer’s and other dementias. These measures include eating a healthy diet, staying socially active, avoiding tobacco and excess alcohol, and exercising both the body and mind.

Modifiable risk factors
Although we can’t change our genes or stop ageing, there are changes that we can make to reduce our risk of dementia, either lifestyle changes as individuals or wider changes across society. A growing body of research evidence exists for 12 potentially modifiable risk factors. We might prevent or delay up to 40% of cases of dementia, if we were able to modify all of the risk factors.

Although behaviour change is difficult and some associations might not be causal, individuals have a huge potential to reduce their dementia risk. Many of the risk factors are also shared with other non-communicable diseases such as heart disease, cancer, diabetes and chronic respiratory diseases.

Keeping active, eating well and engaging in social activities all promote good brain health and may reduce your risk of developing dementia. Keeping your heart healthy, including by avoiding smoking and excessive alcohol consumption, can lower your risk of dementia and other diseases too.

The following is a list of risk factors for dementia along with suggestions of how to counteract them and reduce risk.

Physical inactivity
Regular physical activity is one of the best ways to reduce your risk of dementia. It’s good for your heart, circulation, weight and mental wellbeing. It is recommended that adults aim for either 150 minutes of moderate aerobic activity or 75 minutes of vigorous aerobic activity each week.

Smoking
Smoking greatly increases your risk of developing dementia. You’re also increasing your risk of other conditions, including type 2 diabetes, stroke, and lung and other cancers. It’s never too late – stopping smoking later in life also reduces the risk of dementia.

Excessive alcohol consumption
Alcohol misuse and drinking more than 21 units weekly increase the risk of dementia. The harmful use of alcohol is a causal factor in more than 200 disease and injury conditions. There is a causal relationship between harmful use of alcohol and a range of mental and behavioural disorders, other noncommunicable diseases as well as injuries.

Air pollution
A growing amount of research evidence shows that air pollution increases the risk of dementia. Policymakers should expedite improvements in air quality, particularly in areas with high air pollution.

Head injury
Head injuries are most commonly caused by car, motorcycle, and bicycle accidents; military exposures; boxing, football, hockey and other sports; firearms and violent assaults; and falls. Policymakers should use public health and other policy measures to reduce head injuries.

Infrequent social contact
It is well established that social connectedness reduces the risk of dementia. Social contact enhances cognitive reserve or encourages beneficial behaviours. There is not much evidence for any specific activity protecting against dementia. Joining a club or community group are good ways to stay socially active.

Less education
A low level of education in early life affects cognitive reserve and is one of the most significant risk factors for dementia. Policy should prioritise childhood education for all.

Obesity
Particularly in mid-life, obesity is associated with an increased risk of dementia. Obesity is also associated with other NCDs and can generally be addressed through lifestyle changes such as diet and exercise.

Hypertension
Hypertension (high blood pressure) in mid-life increases a person’s risk of dementia, as well as causing other health problems. Medication for hypertension is the only known effective preventive medication for dementia.

Diabetes
Type 2 diabetes is a clear risk factor for development of future dementia. Whether any particular medication helps with this is unclear, but treatment of diabetes is important for other health reasons.

Depression
Depression is associated with dementia incidence. Depression is part of the prodrome of dementia (a symptom that occurs before the symptoms that are used for diagnosis). It is not clear to what extent dementia may be caused by depression or the reverse, and both may be the case. In any case, it is important to manage and treat depression because is associated with increased disability, physical illnesses and worse outcomes for people with dementia.

Hearing impairment
People with hearing loss have a significantly increased risk of dementia. Using hearing aids seems to reduce the risk. As hearing loss is one of the risk factors which affects the most people, addressing it could result in a large impact on the number of people developing dementia.

Women are more likely to develop Alzheimer’s disease than men, even accounting for the fact that women live longer on average. The reasons for this are unclear.

The greatest risk factor for Alzheimer’s disease and other dementias is increasing age. Although age increases risk, dementia is not a normal part of ageing.

We know there are more than 20 genes which affect a person’s risk of developing dementia. The gene APOE was the first known to increases a person’s risk of developing Alzheimer’s disease, and it is still the strongest risk gene known. There are also genes which directly cause dementia, but these deterministic genes are rare – they are estimated to account for less than 1% of dementia cases, and cause young-onset forms in which symptoms usually develop before the age of 60.