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The Basics of Alzheimer’s Disease and Other Forms of Dementia

A good way to understand Alzheimer’s disease is to look at dementia.

According to the National Institutes of Health, dementia is a generic term that refers to the symptoms that arise from a variety of brain diseases and disorders. While Alzheimer’s disease is the most common form of dementia  (60% to 70% of all demetias), there are more than 100 types of this condition. Dementia impairs more than one domain of cognitive function, which makes it different from brain disorders that affect only one domain such as amnesia (affects memory) and aphasia (affects language skills). It is not loss of memory; rather, it involves the loss of the mind as a whole.

The common characteristic is the loss of brain function that progresses slowly but with increasing severity over time. The usual symptoms are memory loss, confusion, and cognitive difficulties (especially with speech, communication and understanding abilities).

Causes of dementia

Many different ailment can lead to dementia – cancer, high blood pressure, stroke, hypothyroidism, AIDS, vitamin deficiency and poor nutrition, profound depression, Parkinson’s disease, and others. Among the more common causes are:

  • Alzheimer’s disease (AD) – According to the U.S. National Institute of Neurological Disorders and Stroke (NINDS), "Initially, people experience memory loss and confusion. However, the symptoms of AD gradually lead to behavior and personality changes, a decline in cognitive abilities such as decision-making and language skills, and problems recognizing family and friends. AD ultimately leads to a severe loss of mental function. These losses are related to the worsening breakdown of the connections between certain neurons in the brain and their eventual death. This is the most common cause, as the disease alters the brain’s structure and chemical balance, ultimately leading to the death of brain cells."
  • Vascular dementia – this second most common cause of dementia arises from inadequate supply of oxygen to the brain cells, usually as the brain’s blood vessels are damaged after a stroke or a series of mild strokes occurring over time.
  • Creutzfeldt-Jakob disease – infectious agents (called prions) invade the central nervous system and eventually attack the brain, causing dementia.
  • Dementia with Lewy bodies – According to the NIH "the central feature of DLB is progressive cognitive decline, combined with three additional defining features: (1) pronounced “fluctuations” in alertness and attention, such as frequent drowsiness, lethargy, lengthy periods of time spent staring into space, or disorganized speech; (2) recurrent visual hallucinations, and (3) parkinsonian motor symptoms, such as rigidity and the loss of spontaneous movement." Tiny globe-like structures develop in the brain’s nerve cells, eventually causing degeneration of the brain tissues and affecting memory, concentration and language functions.
  • Korsakoff’s syndrome – a brain disorder that results from heavy drinking over an extended period.
  • Fronto-temporal dementia – the frontal lobes of the brain are damaged, leading to significant changes in personality and behavior.
  • AIDS-related cognitive impairment – the AIDS disease may cause brain damage in its later stages, impairing the brain’s cognitive functions.
  • Mild cognitive impairment – a term coined to describe those with memory problems greater than normal for the age but less severe than those associated with Alzheimer’s disease.

Prevalence of dementia

Most forms of dementia become more prevalent as people age. The National Institutes of Health estimates that nearly 10% of people over 65 have conditions leading to Alzheimer’s, and nearly half of those over 85 are affected. 


The onset of dementia is accompanied by very subtle symptoms and years may pass before symptoms become noticeable. Memory loss, though common, does not always indicate dementia. The areas of the brain responsible for language, reasoning, sensory perceptions, and personality may be affected first – especially in those whose symptoms start earlier than age 65. Apart from memory loss, communication problems (whether talking, writing or reading) and volatile mood changes can also indicate dementia.

"The common characteristic of dementia is the loss of brain function, progressing slowly but increasing in severity over time. The most common observable symptoms are memory loss, confusion and cognitive difficulties (especially with speech, communication and understanding abilities)."

Dementia generally has no cure. Some drugs delay progression of the disease in certain individuals and provide temporary relief from symptoms of certain types of dementia.