Alzheimer's disease (AD), also known as Alzheimer disease, or just Alzheimer's, accounts for 60% to 70% of cases of dementia.[1][2] It is a chronic neurodegenerative disease that usually starts slowly and gets worse over time.[1][2] The most common early symptom is difficulty in remembering recent events (short-term memory loss).[1] As the disease advances, symptoms can include problems with language, disorientation (including easily getting lost), mood swings, loss of motivation, not managing self care, and behavioural issues.[1][2] As a person's condition declines, they often withdraw from family and society.[1] Gradually, bodily functions are lost, ultimately leading to death.[3] Although the speed of progression can vary, the average life expectancy following diagnosis is three to nine years.[4][5]
The cause of Alzheimer's disease is poorly understood.[1] About 70% of the risk is believed to be genetic with many genes usually involved.[6] Other risk factors include a history of head injuries, depression, or hypertension.[1] The disease process is associated with plaques and tangles in the brain.[6] A probable diagnosis is based on the history of the illness and cognitive testing with medical imaging and blood tests to rule out other possible causes.[7] Initial symptoms are often mistaken for normal ageing.[1] Examination of brain tissue is needed for a definite diagnosis.[6] Mental and physical exercise, and avoiding obesity may decrease the risk of AD.[6] There are no medications or supplements that decrease risk.[8]
No treatments stop or reverse its progression, though some may temporarily improve symptoms.[2] Affected people increasingly rely on others for assistance, often placing a burden on the caregiver; the pressures can include social, psychological, physical, and economic elements.[9] Exercise programmes are beneficial with respect to activities of daily living and can potentially improve outcomes.[10] Treatment of behavioural problems or psychosis due to dementia with antipsychotics is common but not usually recommended due to there often being little benefit and an increased risk of early death.[11][12]
In 2015, there were approximately 48 million people worldwide with AD.[2] It most often begins in people over 65 years of age, although 4% to 5% of cases are early-onset Alzheimer's which begin before this.[13] It affects about 6% of people 65 years and older.[1] In 2010, dementia resulted in about 486,000 deaths.[14] It was first described by, and later named after, German psychiatrist and pathologist Alois Alzheimer in 1906.[15] In developed countries, AD is one of the most financially costly diseases.[16][17]
At present, there is no definitive evidence to support that any particular measure is effective in preventing AD.[117]
Global studies of measures to prevent or delay the onset of AD have
often produced inconsistent results. Epidemiological studies have
proposed relationships between certain modifiable factors, such as diet,
cardiovascular risk, pharmaceutical products, or intellectual
activities among others, and a population's likelihood of developing AD.
Only further research, including clinical trials, will reveal whether
these factors can help to prevent AD.[118]
Long-term usage of non-steroidal anti-inflammatory drugs (NSAIDs) is associated with a reduced likelihood of developing AD.[124] Evidence also support the notion that NSAIDs can reduce inflammation related to amyloid plaques.[124] No prevention trial has been completed.[124] They do not appear to be useful as a treatment.[125] Hormone replacement therapy, although previously used, may increase the risk of dementia.[126]
Conclusions on dietary components have at times been difficult to ascertain as results have differed between population-based studies and randomised controlled trials.[130] There is limited evidence that light to moderate use of alcohol, particularly red wine, is associated with lower risk of AD.[134] There is tentative evidence that caffeine may be protective.[135] A number of foods high in flavonoids such as cocoa, red wine, and tea may decrease the risk of AD.[136][137]
Reviews on the use of vitamins and minerals have not found enough consistent evidence to recommend them. This includes vitamin A,[138][139] C,[140][141] E,[141][142] selenium,[143] zinc,[144] and folic acid with or without vitamin B12.[145] Additionally vitamin E is associated with health risks.[141] Trials examining folic acid (B9) and other B vitamins failed to show any significant association with cognitive decline.[146] In those already affected with AD adding docosahexaenoic acid, an omega-3 fatty acid, to the diet has not been found to slow decline.[147]
Curcumin as of 2010 has not shown benefit in people even though there is tentative evidence in animals.[148] There is inconsistent and unconvincing evidence that ginkgo has any positive effect on cognitive impairment and dementia.[149] As of 2008 there is no concrete evidence that cannabinoids are effective in improving the symptoms of AD or dementia.[150] Some research in its early stages however looks promising.[151]
The cause of Alzheimer's disease is poorly understood.[1] About 70% of the risk is believed to be genetic with many genes usually involved.[6] Other risk factors include a history of head injuries, depression, or hypertension.[1] The disease process is associated with plaques and tangles in the brain.[6] A probable diagnosis is based on the history of the illness and cognitive testing with medical imaging and blood tests to rule out other possible causes.[7] Initial symptoms are often mistaken for normal ageing.[1] Examination of brain tissue is needed for a definite diagnosis.[6] Mental and physical exercise, and avoiding obesity may decrease the risk of AD.[6] There are no medications or supplements that decrease risk.[8]
No treatments stop or reverse its progression, though some may temporarily improve symptoms.[2] Affected people increasingly rely on others for assistance, often placing a burden on the caregiver; the pressures can include social, psychological, physical, and economic elements.[9] Exercise programmes are beneficial with respect to activities of daily living and can potentially improve outcomes.[10] Treatment of behavioural problems or psychosis due to dementia with antipsychotics is common but not usually recommended due to there often being little benefit and an increased risk of early death.[11][12]
In 2015, there were approximately 48 million people worldwide with AD.[2] It most often begins in people over 65 years of age, although 4% to 5% of cases are early-onset Alzheimer's which begin before this.[13] It affects about 6% of people 65 years and older.[1] In 2010, dementia resulted in about 486,000 deaths.[14] It was first described by, and later named after, German psychiatrist and pathologist Alois Alzheimer in 1906.[15] In developed countries, AD is one of the most financially costly diseases.[16][17]
Prevention
Intellectual activities such as playing chess
or regular social interaction have been linked to a reduced risk of AD
in epidemiological studies, although no causal relationship has been
found.
Medication
Although cardiovascular risk factors, such as hypercholesterolaemia, hypertension, diabetes, and smoking, are associated with a higher risk of onset and course of AD,[119][120] statins, which are cholesterol lowering drugs, have not been effective in preventing or improving the course of the disease.[121][122][123]Long-term usage of non-steroidal anti-inflammatory drugs (NSAIDs) is associated with a reduced likelihood of developing AD.[124] Evidence also support the notion that NSAIDs can reduce inflammation related to amyloid plaques.[124] No prevention trial has been completed.[124] They do not appear to be useful as a treatment.[125] Hormone replacement therapy, although previously used, may increase the risk of dementia.[126]
Lifestyle
People who engage in intellectual activities such as reading, playing board games, completing crossword puzzles, playing musical instruments, or regular social interaction show a reduced risk for Alzheimer's disease.[127] This is compatible with the cognitive reserve theory, which states that some life experiences result in more efficient neural functioning providing the individual a cognitive reserve that delays the onset of dementia manifestations.[127] Education delays the onset of AD syndrome, but is not related to earlier death after diagnosis.[128] Learning a second language even later in life seems to delay getting Alzheimer disease.[129] Physical activity is also associated with a reduced risk of AD.[128]Diet
People who eat a healthy, Japanese, or Mediterranean diet have a lower risk of AD.[130] A Mediterranean diet may improve outcomes in those with the disease.[131] Those who eat a diet high in saturated fats and simple carbohydrates (mono- and disaccharide) have a higher risk.[132] The mediterranean diet's beneficial cardiovascular effect has been proposed as the mechanism of action.[133]Conclusions on dietary components have at times been difficult to ascertain as results have differed between population-based studies and randomised controlled trials.[130] There is limited evidence that light to moderate use of alcohol, particularly red wine, is associated with lower risk of AD.[134] There is tentative evidence that caffeine may be protective.[135] A number of foods high in flavonoids such as cocoa, red wine, and tea may decrease the risk of AD.[136][137]
Reviews on the use of vitamins and minerals have not found enough consistent evidence to recommend them. This includes vitamin A,[138][139] C,[140][141] E,[141][142] selenium,[143] zinc,[144] and folic acid with or without vitamin B12.[145] Additionally vitamin E is associated with health risks.[141] Trials examining folic acid (B9) and other B vitamins failed to show any significant association with cognitive decline.[146] In those already affected with AD adding docosahexaenoic acid, an omega-3 fatty acid, to the diet has not been found to slow decline.[147]
Curcumin as of 2010 has not shown benefit in people even though there is tentative evidence in animals.[148] There is inconsistent and unconvincing evidence that ginkgo has any positive effect on cognitive impairment and dementia.[149] As of 2008 there is no concrete evidence that cannabinoids are effective in improving the symptoms of AD or dementia.[150] Some research in its early stages however looks promising.[151]
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