Alzheimer’s Disease Awareness Month: What causes it? Experts say it may be a mix of multiple risk factors
Old age does not cause the disease, but it is the best known risk factor
Scientists are constantly learning but they do not yet completely understand what causes Alzheimer’s disease in most people. The causes probably include a combination of age-related changes in the brain, along with genetic, environmental, and lifestyle factors. The importance of any one of these factors in increasing or decreasing the risk of Alzheimer’s may differ from person to person.
According to experts, changes in the brain may start much before memory and other cognitive problems appear. So what are the risk factors?
Alzheimer’s is not a normal part of aging. But while older age does not cause the disease, it is the most important known risk factor for the disease. Most individuals with the disease are 65 and older. The number of people with Alzheimer’s doubles about every 5 years beyond age 65, according to the Alzheimer’s Association. About one-third of all people age 85 and older may have Alzheimer’s.
“The percentage of people with Alzheimer’s dementia increases dramatically with age: 3% of people age 65-74, 17% of people age 75-84 and 32% of people age 85 or older have Alzheimer’s dementia,” reveals its 2020 Alzheimer’s disease facts and figures report.
Scientists are learning how age-related changes in the brain may harm neurons and affect other types of brain cells to contribute to Alzheimer’s damage. These age-related changes include atrophy or shrinking of certain parts of the brain, inflammation, vascular damage, production of unstable molecules called free radicals, and breakdown of energy production within cells.
More women than men have Alzheimer’s or other dementias. The prevailing reason that has been stated for this is that women live longer than men on average. Other factors are also being investigated.
Family history and genetics
Many people worry about developing Alzheimer’s disease, especially if a family member has had it. Having a family history (for example, a parent or sibling) of the disease does not mean for sure that you will also have it. But it may mean you are more likely to get it.
People’s genes, which are inherited from their biological parents, can affect how likely they are to develop Alzheimer’s. Genetic risk factors are changes or differences in genes that can influence the chance of getting a disease. These risk factors are the reason some diseases run in families. Both early-onset (happens from 30-60 years old) and late-onset (happens from the mid-60s and older) Alzheimer’s are said to have a genetic component.
“Researchers have not found a specific gene that directly causes late-onset Alzheimer's disease. However, having a genetic variant of the apolipoprotein E (APOE) gene on chromosome 19 does increase a person's risk. Also, scientists have identified a number of regions of interest in the genome (an organism’s complete set of DNA) that may increase or decrease a person’s risk for late-onset Alzheimer’s to varying degrees,” according to the National Institutes of Health. Find more details here.
Experts, however, suggest that it is important to know about one’s family health history to discover patterns of disease and risk factors in the family. This information can help a person decide whether he/she should see a doctor. “Families have many things in common, including their genes, environment and lifestyle. Together, these things may offer clues to diseases, like late and early-onset Alzheimer’s, that can run in a family,” says the NIH.
Many, but not everyone with Down syndrome, develop Alzheimer’s. This may be because people with Down syndrome have an extra copy of chromosome 21, which contains the gene that generates harmful amyloid, say experts.
“This gene produces a specific protein called amyloid precursor protein (APP). Too much APP protein leads to a buildup of protein clumps called beta-amyloid plaques in the brain. By age 40, almost all people with Down syndrome have these plaques, along with other protein deposits, called tau tangles, which cause problems with how brain cells function and increase the risk of developing Alzheimer’s dementia,” explains the NIH.
Mild cognitive impairment
While not all people with mild cognitive impairment develop dementia, people with this condition do have a significantly increased risk of dementia compared to the rest of the population. “Some people with memory problems have a condition called mild cognitive impairment, or MCI. MCI has several types. The type most associated with memory loss is called amnestic MCI. About 8 of every 10 people who fit the definition of amnestic MCI go on to develop Alzheimer's disease within 7 years. In contrast, 1 to 3 percent of people older than 65 who have normal cognition will develop Alzheimer's in any one year,” notes the NIH.
According to the Alzheimer’s Association, there is a link between head injury and future risk of dementia. The risk of dementia increases with the number of traumatic brain injuries sustained.
Health, environmental and lifestyle factors
Research suggests that multiple factors beyond genetics may play a role in the development and course of Alzheimer’s disease. Some say that early-life factors may also play a role. Accordingly, experts are studying whether education, diet and environment play a role in developing the disease. For example, studies have linked higher levels of education with a decreased risk of dementia.
There are also differences in dementia risk among racial groups and sexes — all of which are being studied to better understand the causes of Alzheimer’s disease and to develop effective treatments and preventions for all people.
Poor sleep patterns have been associated with an increased risk of Alzheimer’s disease. Scientists are finding more evidence that some of the risk factors for heart disease and stroke, such as high blood pressure and high cholesterol may increase the risk of Alzheimer’s. Lack of exercise, obesity, poorly controlled type diabetes may also increase the risk, says Mayo Clinic.
“Many factors that increase the risk of cardiovascular disease are also associated with a higher risk of dementia. These factors include smoking and diabetes. Some studies propose that impaired glucose processing (a precursor to diabetes) may also result in an increased risk for dementia,” say experts.
Ongoing research could help experts understand whether and how reducing risk factors for these conditions may also reduce the risk of Alzheimer’s. “Researchers have begun studying combinations of health factors and lifestyle behaviors (for example, blood pressure as a health factor and physical activity as a lifestyle behavior) to learn whether combinations of risk factors better identify Alzheimer’s and dementia risk than individual risk factors. They are also studying whether intervening on multiple risk factors simultaneously is more effective at reducing risk than addressing a single risk factor,” suggests the Alzheimer’s Association.