Many people, especially middle-aged and older friends may have this experience, once over 50 years old, you feel that memory can not, before a glance, listen to a time to remember things, now especially love to forget. Although sometimes feel that you should think of some way, but often a “old, brain can not” after, will not care too much. Perhaps you don’t know that this can sometimes delay the important things that could have been detected and treated early, but the best time to prevent and treat Alzheimer’s disease is missed. A few examples: Former U.S. President Reagan is a prime example. In the early 1990s, Reagan showed signs of memory loss, such as forgetting what he had just said. Once in a conversation his daughter mentioned a movie role Reagan had played, but Reagan couldn’t remember it. Within a year, Reagan was diagnosed with Alzheimer’s disease, but was past the early stages of the disease. Eventually, he didn’t recognize anyone except his wife Nancy, and couldn’t even remember that he had served two terms as president of the United States. One high school physics teacher extraordinaire, Mr. Gao, had a colleague report that the quality of his lectures was worse than in the past a year before he retired, while he thought his colleagues were jealous of him. At this time, the special teacher’s son opened a private school, so Mr. Gao retired to teach at the private school and continued to teach physics. Students reported that Mr. Gao often repeated what he had already said in class and often failed to answer questions from his classmates. Mr. Gao’s son had to personally investigate his father’s lecturing ability, and as a result, Mr. Gao was diagnosed with Alzheimer’s disease by a physician at the hospital. The physician said that Mr. Gao had actually lost his voice two years earlier and often could not call his old colleagues by name, so he should have been seen in the hospital by then. Several concepts: Dementia is a clinical syndrome, is a persistent impairment of acquired intellectual function, is in the absence of consciousness impairment, according to memory, speech, visuospatial function, cognition (abstract thinking, calculation, judgment and executive ability, etc.) and personality and other five mental activities, at least one of the memory, cognition and another significant deficit, and has lasted for more than 6 months is dementia. Alzheimer’s disease is defined as a sustained impairment in the nature of acquired intelligence that occurs in old age, that is, a largely irreversible loss of intelligence and reduced social adaptation caused by organic brain damage. The main manifestations are: loss of abstract thinking, inadequate reasoning and planning, and attention deficits in intelligence; loss of interest and initiative, slowness or difficulty in inhibiting, social misbehavior, and unconventionality in personality; amnesia, poor topographical, visual, and spatial orientation in memory; and speech disfluency and general deficits in verbal cognition. ”Alzheimer’s disease” or “dementia of old age” refers to dementia that occurs in old age due to various etiologies. Based on recent clinical and pathological studies, there are three main causes of dementia at home and abroad: Alzheimer’s disease. It used to be called “progeria”. Multiple infarct dementia. It used to be called “cerebral atherosclerotic dementia”. Other causes of dementia. These include brain tumors, traumatic brain injury, infections, poisoning, and metabolic disorders that cause dementia in old age. Clinical manifestations of Alzheimer’s disease: 1. Onset in old age, but also after age 50. 2. Dementia syndrome as the main clinical manifestation. The majority of the patients are conscious, and most of the dementia appears slowly and is not easily noticed in the early stages. 3. Progressive decline in intelligence and thinking ability until total decline. 4. Emotional and personality changes. 5. Mental disorders. 6. General mental decline. The common causes of dementia are: (1), brain degenerative diseases: there are many kinds of dementia caused by brain degenerative diseases, the most common is Alzheimer’s disease dementia, which is also called progeria dementia when it develops in the early age. The onset of dementia is slow and progressive. In addition, there are Pick’s disease, Tinton’s chorea dementia, progressive supranuclear palsy, Parkinson’s disease dementia, and so on. These latter dementias are relatively uncommon. (2) Cerebrovascular disease: The most common ones are multiple cerebral infarct dementia, which is caused by a series of multiple minor cerebral ischemic attacks that accumulate many times and cause substantial cerebral infarction. In addition, there are subcortical vascular dementia and acute onset cerebrovascular dementia, which can rapidly develop into dementia after a series of strokes caused by cerebral hemorrhage and cerebral embolism, and a few can also be caused by a single large cerebral infarction. In short, cerebrovascular disease is also a more common cause of dementia. (3) Genetic factors: Many studies at home and abroad have proved that the offspring of Alzheimer’s patients have more chances to suffer from this disease. However, the mode of inheritance is still unclear. Some people believe that it is dominant genetic inheritance; some believe that it is recessive genetic inheritance; some believe that it is polygenic autosomal recessive inheritance, and the genetic effect can be governed by environmental factors and mutations of genetic factors, which interrupt its genetic effect. There are also some studies that consider Alzheimer’s disease as a non-genetic disease, such as vascular dementia, which is not directly related to heredity. (4) Endocrine disorders: Hypothyroidism and parathyroidism may cause dementia. (5) Nutritional and metabolic disorders: The brain tissue and its functions are damaged due to nutritional and metabolic disorders, resulting in dementia. For example, various organ-induced encephalopathy, like renal encephalopathy, which is chronic renal failure and uremia causing ischemia and hypoxia in the brain, can lead to dementia; others such as hepatic encephalopathy and pulmonary encephalopathy can lead to dementia. Severe nutritional deficiencies, such as vitamin B1 and B12 as well as niacin and folic acid deficiencies can lead to dementia. Diabetes and hyperlipidemia can cause atherosclerosis in large and medium arteries, and thickening of the basement membrane of small vessels and microvessels can cause cerebral infarction and cerebral hemorrhage, leading to vascular dementia. (6), tumors: malignant tumors cause metabolic disorders can lead to dementia, brain tumors can also directly damage brain tissue leading to dementia. (7), drugs and other substances poisoning: alcoholism, chronic sprinkler poisoning caused by Alzheimer’s disease is not uncommon, in is not yet recognized. Long-term exposure to aluminum, mercury, gold, silver, arsenic and lead, etc., poorly protected, causing chronic poisoning can lead to dementia. Carbon monoxide poisoning is also a common cause of acute dementia. (8), AIDS: AIDS is one of the causes of dementia. It is now known that progressive dementia can occur in the early stages of AIDS in the elderly, and it has been shown that the central nervous system can be directly infected with human immunodeficiency virus (HIV). (9), syphilis: syphilis spirochetes can invade the brain, producing psychiatric and neurological symptoms, eventually leading to paralysis and increasing mental retardation and personality changes, the so-called paralytic dementia. (10), Other: Traumatic brain injury, persistent seizures of epilepsy, and normal pressure hydrocephalus can cause dementia. In addition, long-term emotional depression, isolation, widowhood, illiteracy, low language level, and lack of physical and mental exercise in the elderly can also accelerate the process of brain aging and induce dementia.