Dementia and Alzheimer's disease

Dementia

Dementia is a serious brain disorder that usually involves loss of memory, followed by loss of ability to carry out daily activities. Demented persons may ask the same questions repeatedly, forgetting answers they heard hours or even minutes earlier. They lose track of time and may become lost in familiar surroundings. They lose the ability to follow simple directions. Severely demented people are unable to recognize their closest relatives, forget how to eat and dress, and may lose all but the simplest forms of language expression. They become entirely dependent and helpless, unable to keep themselves clean, safe, and well-fed.

There are many causes of dementia, some of which are reversible. For example, symptoms of dementia may occur after a head injury or as the result of poor nutrition or a vitamin deficiency (especially of B12). Another cause is heavy metal (lead or mercury) poisoning. Temporary dementia may also result from high fever or dehydration, reactions to drugs, or insufficient thyroid hormone (hypothyroidism). In the elderly, irreversible dementia is usually caused by either Alzheimer's disease or "multi-infarct dementia" -- a condition resulting from a disease of the arteries supplying blood to the brain. The only way to definitely determine the cause of senile dementia is to examine the patient's brain tissue.

Alzheimer's disease

Alzheimer's disease (AD) is a form of dementia. It was first described in 1906 by a German doctor named Alois Alzheimer, who was examining microscopic sections from the brain of a middle-age woman. She had become progressively and severely demented and then died.

In her brain, Dr. Alzheimer observed abnormal clumps of glassy yellowish material (amyloid plaques) and tangled black bundles of fibers (neurofibrillary tangles). Such plaques and tangles are now considered the hallmark of Alzheimer's disease. Because the patient in question was not very old, the disease was labeled a "pre-senile" or premature form of dementia. Only later did researchers discover that the majority of elderly people who became "senile" also have plaques and tangles in their brains, like those that Dr. Alzheimer saw.

We now know that Alzheimer's disease is the most common cause of irreversible, progressive dementia in the elderly. As many as 4.5 million Americans may suffer from it. Although younger people occasionally get the disease, it is far more frequent in people over age 60, and the risk of developing it increases with age. The rate for people ages 65 to 74 is about 5 percent; that increases to nearly 50 percent for people ages 85 and older. Nonetheless, Alzheimer's disease does not represent "normal" brain aging. Instead, it is a disease process that occurs in some, but not all, aging brains.

Symptoms and treatments

Alzheimer's disease first affects areas of the brain responsible for thought, memory, and language. Those plaques and tangles that Dr. Alzheimer saw mark areas of the brain where nerve cells have died, including those vital to memory and other mental abilities. As nerve cells drop out, vital connections to and from other nerve cells are lost. It is as if critical switches in a huge telephone center burn out and prevent transmission of incoming signals. In other words, the disease impairs thinking and memory by disrupting transmission of vital messages.

Despite all that we have learned about Alzheimer's, we still do not fully understand the cause. Many scientists are hard at work trying to unravel the processes that lead to nerve cell loss in the brain. Some believe that processing of a protein that becomes amyloid holds the key, because amyloid is the substance that forms those plaques in the brain. Others think that the formation of amyloid is part of a defense reaction against cell death, and that other processes leading to nerve cell destruction are more important. One such process might be damage by oxygen free radicals (oxidative stress), which seems related to other chronic diseases, and perhaps to aging itself. Humans with early signs of dementia frequently have high levels of compounds that are markers of ongoing oxidative damage, in their blood, urine, and spinal fluid.

One thing is clear: Inheritance plays an important role in the disease. Certain genes greatly increase the risk that a person will develop it, whereas others seem to protect against it.

Because we do not fully understand the cause(s) of the disease, the search for a cure has been challenging. In studies of aging dogs, animals fed diets high in antioxidant compounds either did not show Alzheimer's-like brain damage or developed it much later than control dogs fed a normal canine diet. Similar studies with humans are not yet conclusive. However, a regimen of regular exercise - both physical and mental - along with a diet rich in fruits and vegetables (natural anti-oxidants), does seem to have preventive effects.

Only with continued research, requiring support from public and private sources, will we finally determine the fundamental cause of this scourge of the elderly. The Kronos Longevity Research Institute has been working on better methods to define and measure ongoing oxidative stress. Perhaps this research will eventually contribute to better methods to prevent or cure Alzheimer's disease.