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What Is Alzheimer's Disease?

Alzheimer's disease or Alzheimer's-type dementia is a progressive degeneration of brain tissue that primarily strikes people over age 65. It is the most common cause of dementia in this age group and is marked by a devastating mental decline. Intellectual functions such as memory, comprehension and speech deteriorate.

Attention tends to stray, simple calculations become impossible and ordinary daily activities grow increasingly difficult, with bewilderment and frustration. These symptoms tend to worsen at night. Dramatic mood swings occur — outbursts of anger, bouts of fearfulness, and periods of deep apathy. The sufferer, increasingly disoriented, may wander off and become lost. Physical problems, such as an odd gait or a loss of coordination, gradually develop. Eventually, the patient may become physically helpless, incontinent and unable to communicate.

Alzheimer's disease can run its course from insidious onset to death in just a few years, or it may play out over a period of as long as 20 years. More often, however, people suffer with Alzheimer's disease about nine years. By the age of 80, about one person out of three has the disease. Women are more susceptible than men and half of all nursing home residents suffer from Alzheimer's or related disorders.

What Causes It?

Although many people develop Alzheimer's disease as they grow older, the disease is not a natural result of aging. It is an abnormal condition whose causes continue to be investigated.

The gradual loss of brain function that characterizes Alzheimer's disease seems to be due to two main forms of nerve damage:

• Nerve fibers grow tangled (neurofibrillary tangles)
• protein deposits known as plaques build up in the brain (Figure 2).

Researchers are not yet sure why or how these processes occur, but some of the most promising recent research points to a normally occurring blood protein called ApoE (for apolipoprotein E), which is required for the transport of fatty substances in the body.

As with all proteins, the form of ApoE that each person has in their body is genetically determined, and several different types have been identified — some of them apparently associated with a higher risk of Alzheimer's. It may be that certain forms of ApoE lead to the nerve damage.

Another possibility is that the protein, perhaps working in combination with other substances, is involved in the formation of the plaques. Whether or not ApoE partly causes Alzheimer's disease, genes almost certainly play a role in the disease and a person with a parent who had Alzheimer's disease is at higher risk.

Other causes have been proposed. One theory suggests that ingesting tiny particles of aluminum — from cookware, for example — may lead to Alzheimer's. Another proposes a link between plaque formation and free radicals — unstable, free-ranging molecules that can produce destructive chemical reactions. Both theories are controversial and unproven. Indeed, many researchers now consider the link between Alzheimer's and aluminum extremely questionable.

Another controversy centers on zinc. But the connection between zinc and Alzheimer's remains unclear. It is thought that at low levels zinc may be protective but at higher doses it may be harmful. For one thing, scientists remain unsure whether plaques cause Alzheimer's or are themselves a result of the disease. If the latter, zinc's ability to form plaques might be unrelated to what causes Alzheimer's disease in the first place.

There is some evidence that people with high blood pressure and high cholesterol have an increased chance of developing Alzheimer's. In a minority of cases, trauma may be a contributing factor. The more severe the head injury, the greater the risk of Alzheimer's dementia later in life.

While many of these theories are still being studied, it is clear that the biggest risk factors associated with developing Alzheimer's disease are increasing age and family history.