Risk Factors & Complications
Risk Factors for Alzheimer’s Disease
AD is the most common cause of irreversible cognitive impairment among the elderly. Scientists have identified several factors that increase the risk of developing AD. Some of the risk factors for AD cannot be prevented. However, research suggests that there may be other factors that can be influenced and prevented.
Non-Modifiable Risk Factors of AD
Increasing age, family history, and genetics are the common risk factors of AD, which although known for years, cannot be controlled.Increasing Age
Increasing age is the most important known risk factor for AD. Although it is not considered as a normal part of aging, the risk of developing AD doubles about every five years after the age 65 years. Almost 50 percent people in the age group of 85 years and above develop AD.
According to the latest statistics by Centers for Disease Control and Prevention (CDC), AD is the fifth leading cause of death among people aged 65 years and above. Very old people aged 85 years and above have a 5.4 times greater risk of dying from AD than people aged 75 to 84 years.
Family History and Genetics
Family history is a known risk factor for AD and predictor of early-onset AD. This means the risk of developing AD after age of 65 years, is higher if you have a blood relative, such as parents and/or siblings, with AD. Scientists suspect involvement of genetic factors, as AD shows tendency to run in families.
According to a recent study conducted at Duke University Medical Center, close family members of a person with AD, are more than twice as likely as those without a family history to develop buildup of brain plaques.
Scientists have identified several risk-factor genes that increase the risk of AD. There are two types of genes that can play a role in affecting whether a person develops a disease or not. These are known as risk genes and deterministic genes.Risk Genes
The risk genes increase the likelihood of inheriting a disease, but do not guarantee it. One of the risk genes is called Apolipoprotein E (APOE). The ɛ4 variant of the APOE gene is responsible for about 50 percent of the heritability of late-onset AD (AD occurring after age of 60 to 65 years.)Deterministic Genes
Inheriting deterministic genes confirm the presence of disease. When AD is caused by these deterministic variations, it is called as “Familial AD” which is an early-onset AD. There are only few hundred families worldwide who have been recognized to carry these genes from generation to generation. The family members carrying these genes generally develop symptoms before age 60 years; sometimes the symptoms may appear as early as 30 or 40 years.
Modifiable Risk Factors of AD
Unlike age and genetic factors, some lifestyle factors associated with AD can be controlled. These include head injuries, lifestyle factors, such as smoking, lack of exercise, uncontrolled diabetes, hypertension, andcognitive stimulation.
Some clinical research suggests that people who have had severe or repeated head injuries in the past are at increased risk of developing AD when they get old. The worse the head injury, higher is the risk of AD.
According to a study, moderate head injury is associated with a two-fold increase in risk, whereas severe head injury increases risk by four times.
- Severe Head Injury: When a person needs admission to a hospital and remains unconscious or shows memory loss for 24 hours or more.
- Moderate Injury: When a person remains unconscious or has memory loss lasting no more than 30 minutes after the injury.
How Can You Prevent Head Injuries?
Research shows that some lifestyle related risk factors may have a possible role in development of AD. Many of these are potentially modifiable and include smoking, physical inactivity, diabetes, education, social engagement, cognitive stimulation, and diet.
Available scientific evidence considers smoking to be a significant risk factor for AD. According to a study, heavy smoking (more than two packs a day) in midlife is associated with a greater than 100 percent increase in the risk of AD. One study reports that smokers who quit may have a lower risk of AD compared with those who continue to smoke.
Clinical evidence suggests that physical inactivity or lack of exercise, which is one of the important risk factors for heart disease, diabetes, and obesity, may also contribute to the development of AD. New human research now suggests that regular physical activity is beneficial for the prevention and management of AD. The exact mechanism by which physical activity may prevent AD is not known. However, experimental studies suggest that physical activity may promote the maintenance of grey matter brain volume, and slow the rate of cognitive decline. Regular physical activity is also believed to protect the brain cells and tissues from oxidative stress, which is involved in pathogenesis of AD.
One clinical study reported that people who did some physical activity (walking, swimming etc.) had 29 to 41 percent lower risk of developing AD as compared to people who were physically inactive. Vigorous physical activity (aerobic dancing, jogging) was associated with a 37 to 50 percent lower risk. From the available clinical data it is clear that physical activity is beneficial in the prevention of AD.
Research has found an increased risk of developing AD in people with diabetes. One study reported that individuals with clinically verified AD are more likely to have a history of diabetes. Although the mechanism for this association is not clear, scientists believe that diabetes and AD may share some pathological features. Impairment of insulin signaling, inflammation, and oxidative stress seen in diabetes may also promote the pathology of AD.
Furthermore, insulin resistance is thought to be associated with a decrease in glucose uptake by neurons and increase in Beta-Amyloid production.
Clinical studies are underway to find if controlling diabetes can lower the risk of diabetes. A small pilot study led by Department of Veterans Affairs (VA) researchers reported promising results with a nasal insulin spray in improving memory, thinking skills, and functional ability in people with AD. Considering the evidence that links diabetes and AD, it appears that controlling diabetes may show promising results in reducing AD risk.
Hypertension (High Blood Pressure)
Research suggests that blood pressure is increased in people with AD decades before the onset of the disease. High blood pressure has also been linked to pathological features of AD, such as formation of neurofibrillary tangles and brain atrophy (shrinking of brain). Several observational studies suggest that use of blood pressure lowering drugs decreases the risk of AD. Even though hypertension only causes moderate increase in risk of AD, better treatment of hypertension may show immense effects in preventing AD.
Lack of Cognitive Stimulation
Lack of brain stimulating activities, is considered as a risk factor for developing AD. Therefore, keeping your brain active with social engagement or intellectual stimulation can lower the risk of AD. Studies also show that cognitive stimulation and socialization improves mood and quality of life in people with AD. Cognitive rehabilitation combined with drug treatment can improve cognitive and functional performance of people with mild AD.
Evidence suggests that people with less education can improve their cognitive function by doing brain stimulating activities, such as reading, learning new things, solving crossword puzzles, or other social activities.Infections
Infection caused by various pathogens, such as viruses and bacteria may constitute a risk factor for AD. The infections of central nervous system caused by Herpes simplex virus type 1 and Chlamydophila pneumonia have been considered as possible agents in the development of AD. Early detection and treatment against infection may delay or even prevent the future development of AD.
According to the scientists, high intake of trans-unsaturated (hydrogenated) fats may increase the risk of AD. Conversely, sticking to Mediterranean dietary pattern can lower risk of dementia and ultimately AD. The Mediterranean diet consists of a high consumption of vegetables, fruits, legumes and cereals, a high intake of olive oil as the main source of fat, a moderate intake of fish. This diet pattern has low-to-moderate intake of dairy products and low consumption of meat and poultry, with wine consumed in low-to-moderate amounts during meals.
How Can You Control Lifestyle-related Risk Factors of AD?
Last Reviewed on: August 02, 2014
Reviewed By: Dr. Akshya Vasudev, MBBS, MD, MRCPsych, PG Cert Med Edu