Mental Activity

"Use it or lose it" might be applied to the brain when it comes to dementia. Intellectual activities help keep the mind in shape in the older days. Activities such as reading, playing cards and board games and playing a musical instrument prevent dementia of both Alzheimer's and vascular dementia. The risk decreases proportionally to the frequency of activity.
Not only activities during spare time seem to prevent dementia. The kind of occupation also matters, especially during the thirties, forties and fifties. A good job in this case is any mentally demanding one.
Why activity contributes to prevent dementia could be explained by a "brain reserve" built up by the brain: additional connections between neurons are created, connections more resistant to the deterioration seen in dementia.

Physical activity
Since vascular dementia is the second most common form of dementia (after Alzheimer's disease), decreasing risk factors for cerebrovascular disease also decreases the risk factors for dementia. Thus, physical exercise, having good blood cholesterol, healthy body weight and blood pressure lowers the risk of developing dementia. An active lifestyle can almost halve the risk compared to a sedentary one.
The effect of physical activity is not limited to vascular effects. For instance, it can give rise to new neurons in the brain, as well as releasing a substance that can protect them.
Some studies say Alzheimer's and other dementias may be caused by high blood pressure, since it can cause blood vessel damage by constricting them.

Diet
Obesity increases the risk of any dementia, but Alzheimer's in particular. However, what kind of food eaten also matters. Fish consumption reduces the risk of Alzheimer's. Fish is high in docosahexaenoic acid, an omega-3 fatty acid, especially in cold water fish such as salmon, tuna and halibut.
Vegetables and nuts also benefit, because of their high content of polyunsaturated fats. Non-fish meat, on the other hand, increases the risk of Alzhemer's, by its high content of saturated fat. The moderate consumption of alcohol may reduce risk through improving vascular health and other mechanisms.
Drinking small amounts of alcohol may be protective against dementia and Alzheimer's disease but not for vascular dementia or cognitive decline.

Sleep pattern
Prolonged, more than nine hours, sleep duration (night-time sleep and daytime napping) may be associated with an increased risk of dementia

Fixed cognitive impairment
Various types of brain injury, occurring as a single event, may cause irreversible but fixed cognitive impairment. Traumatic brain injury may cause generalised damage to the white matter of the brain (diffuse axonal injury), or more localised damage (as also may neurosurgery). A temporary reduction in the brain's supply of blood or oxygen may lead to hypoxic-ischemic injury. Strokes (ischemic stroke, or intracerebral, subarachnoid, subdural or extradural hemorrhage) or infections (meningitis and/or encephalitis) affecting the brain, prolonged epileptic seizures and acute hydrocephalus may also have long-term effects on cognition. Excessive alcohol use may cause either alcohol dementia or Korsakoff's psychosis (and certain other recreational drugs may cause substance-induced persisting dementia); once overuse ceases, the cognitive impairment is persistent but non-progressive.

Slowly progressive dementia
Dementia which begins gradually and worsens progressively over several years is usually caused by neurodegenerative disease, that is, by conditions affecting only or primarily the neurons of the brain and causing gradual but irreversible loss of function of these cells. Less commonly, a non-degenerative condition may have secondary effects on brain cells, which may or may not be reversible if the condition is treated.
The causes of dementia depend on the age at which symptoms begin. In the elderly population (usually defined in this context as over 65 years of age), a large majority of cases of dementia are caused by Alzheimer's disease, vascular dementia or both. Dementia with Lewy bodies is another fairly common cause, which again may occur alongside either or both of the other causes[20][21][22]. Hypothyroidism sometimes causes slowly progressive cognitive impairment as the main symptom, and this may be fully reversible with treatment. Normal pressure hydrocephalus, though relatively rare, is important to recognise since treatment may prevent progression and improve other symptoms of the condition. However, significant cognitive improvement is unusual.
Dementia is much less common under 65 years of age. Alzheimer's disease is still the most frequent cause, but inherited forms of the disease account for a higher proportion of cases in this age group. Frontotemporal lobar degeneration and Huntington's disease account for most of the remaining cases[23]. Vascular dementia also occurs, but this in turn may be due to underlying conditions (including antiphospholipid syndrome, CADASIL, MELAS, homocystinuria, moyamoya and Binswanger's disease). People who receive frequent head trauma, such as boxers or some martial artists, are at risk of dementia pugilistica. An association between coeliac disease and dementia has been proposed, but this is controversial.
In young adults (up to 40 years of age) who were previously of normal intelligence, it is very rare to develop dementia without other features of neurological disease, or without features of disease elsewhere in the body. Most cases of progressive cognitive disturbance in this age group are caused by psychiatric illness, alcohol or other drugs, or metabolic disturbance. However, certain genetic disorders can cause true neurodegenerative dementia at this age. These include familial Alzheimer's disease, metachromatic leukodystrophy, SCA17 (dominant inheritance); adrenoleukodystrophy (X-linked); Gaucher's disease type 3, Niemann-Pick disease type C, pantothenate kinase-associated neurodegeneration, Tay-Sachs disease and Wilson's disease (all recessive). Wilson's disease is particularly important since cognition can improve with treatment.
At all ages, a substantial proportion of patients who complain of memory difficulty or other cognitive symptoms are suffering from depression rather than a neurodegenerative disease. Vitamin deficiencies and chronic infections may also occur at any age; they usually cause other symptoms before dementia occurs, but occasionally mimic degenerative dementia. These include deficiencies of vitamin B12, folate or niacin, and infective causes including cryptococcal meningitis, HIV, Lyme disease, progressive multifocal leukoencephalopathy, subacute sclerosing panencephalitis, syphilis and Whipple's disease.

Rapidly progressive dementia
Creutzfeldt-Jakob disease typically causes a dementia which worsens over weeks to months. The common causes of slowly progressive dementia also sometimes present with rapid progression: Alzheimer's disease, dementia with Lewy bodies, frontotemporal lobar degeneration (including corticobasal degeneration and progressive supranuclear palsy). On the other hand, encephalopathy or delirium may develop relatively slowly and resemble dementia. Possible causes include brain infection (viral encephalitis, subacute sclerosing panencephalitis, Whipple's disease) or inflammation (limbic encephalitis, Hashimoto's encephalopathy, cerebral vasculitis); tumours such as lymphoma or glioma; drug toxicity (e.g. anticonvulsant drugs); metabolic causes such as liver failure or kidney failure; and chronic subdural hematoma.

Dementia as a feature of other conditions
There are many other medical and neurological conditions in which dementia only occurs late in the illness, or as a minor feature. For example, a proportion of patients with Parkinson's disease develop dementia, though widely varying figures are quoted for this proportion[citation needed]. When dementia occurs in Parkinson's disease, the underlying cause may be dementia with Lewy bodies or Alzheimer's disease, or both. Cognitive impairment also occurs in the Parkinson-plus syndromes of progressive supranuclear palsy and corticobasal degeneration (and the same underlying pathology may cause the clinical syndromes of frontotemporal lobar degeneration). Chronic inflammatory conditions of the brain may affect cognition in the long term, including Behçet's disease, multiple sclerosis, sarcoidosis, Sjögren's syndrome and systemic lupus erythematosus. Although the acute porphyrias may cause episodes of confusion and psychiatric disturbance, dementia is a rare feature of these rare diseases

Aside from those mentioned above, inherited conditions which may cause dementia alongside other features include:
- Alexander disease
- Canavan disease
- cerebrotendinous xanthomatosis
- DRPLA
- fragile X-associated tremor/ataxia syndrome
- glutaric aciduria type 1
- Kufs' disease
- Krabbe's disease
- maple syrup urine disease
- neuroacanthocytosis
- organic acidemias
- Pelizaeus-Merzbacher disease
- urea cycle disorders
- Sanfilippo syndrome type B
- spinocerebellar ataxia type 2

Recent memory loss. All of us forget things for a while and then remember them later. People who have dementia often forget things, but they never remember them. They might ask you the same question over and over, each time forgetting that you've already given them the answer. They won't even remember that they already asked the question.

Difficulty performing familiar tasks. People who have dementia might cook a meal but forget to serve it. They might even forget that they cooked it.

Problems with language. People who have dementia may forget simple words or use the wrong words. This makes it hard to understand what they want.

Time and place disorientation. People who have dementia may get lost on their own street. They may forget how they got to a certain place and how to get back home.

Poor judgment. Even a person who doesn't have dementia might get distracted. But people who have dementia can forget simple things, like forgetting to put on a coat before going out in cold weather. Problems with abstract thinking. Anybody might have trouble balancing a checkbook, but people who have dementia may forget what the numbers are and what has to be done with them.

Misplacing things. People who have dementia may put things in the wrong places. They might put an iron in the freezer or a wristwatch in the sugar bowl. Then they can't find these things later.

Changes in mood. Everyone is moody at times, but people who have dementia may have fast mood swings, going from calm to tears to anger in a few minutes.

Personality changes. People who have dementia may have drastic changes in personality. They might become irritable, suspicious or fearful.

Loss of initiative. People who have dementia may become passive. They might not want to go places or see other people.

Dementia (meaning "deprived of mind") is a serious cognitive disorder. It may be static, the result of a unique global brain injury or progressive, resulting in long-term decline in cognitive function due to damage or disease in the body beyond what might be expected from normal aging. Although dementia is far more common in the geriatric population, it may occur in any stage of adulthood. This age cutoff is defining, as similar sets of symptoms due to organic brain syndrome or dysfunction, are given different names in populations younger than adult. Up to the end of the nineteenth century, dementia was a much broader clinical concept

Dementia is a non-specific illness syndrome (set of signs and symptoms) in which affected areas of cognition may be memory, attention, language, and problem solving. It is normally required to be present for at least 6 months to be diagnosed;[2] cognitive dysfunction that has been seen only over shorter times, in particular less than weeks, must be termed delirium. In all types of general cognitive dysfunction, higher mental functions are affected first in the process. Especially in the later stages of the condition, affected persons may be disoriented in time (not knowing what day of the week, day of the month, or even what year it is), in place (not knowing where they are), and in person (not knowing who they are or others around them). Dementia, though often treatable to some degree, is usually due to causes that are progressive and incurable.

Symptoms of dementia can be classified as either reversible or irreversible, depending upon the etiology of the disease. Less than 10 percent of cases of dementia are due to causes that may presently be reversed with treatment. Causes include many different specific disease processes, in the same way that symptoms of organ dysfunction such as shortness of breath, jaundice, or pain are attributable to many etiologies. Without careful assessment of history, the short-term syndrome of delirium (often lasting days to weeks) can easily be confused with dementia, because they have all symptoms in common, save duration, and the fact that delirium is often associated with over-activity of the sympathetic nervous system.[citation needed] Some mental illnesses, including depression and psychosis, may also produce symptoms that must be differentiated from both delirium and dementia.[3] Chronic use of substances such as alcohol as well as chronic sleep deprivation can also predispose the patient to cognitive changes suggestive of dementia