Here is a phrase you’ll hear often among the 70-plus gang: What good is being physically healthy if your brain is gone?

One of the big fears as we age is dementia, the progressive decline—beyond what might be expected from normal aging—in cognitive function due to damage or disease in the brain. By the age of 70 only about 10 percent of this population suffers from significant memory loss problems, but by the age of 85 about half of the people suffer from some sort of dementia. And the most common cause of dementia is Alzheimer’s disease.

Alzheimer’s is an irreversible brain disorder without a cure that affects 4.5 million Americans. Put simply, it is a progressive degeneration of the brain’s nerve cells, or neurons. For reasons unknown, these neurons break their connections with other neurons and ultimately die. Over time, this terrible affliction leads to loss of memory, impaired thinking and language skills, and personality changes.

What we know about Alzheimer’s is that two types of unusual lesions clog the brains of those with the disease. There are sticky clumps of protein fragments and cellular material called beta-amyloid plaques that form outside and around the neurons, as well as twisted protein fibers called neurofibrillary tangles that build up inside the nerve cells.

But even though we see these plaques and tangles in the postmortem brains of people with Alz-heimer’s, we don’t know which come first. Scientists are unclear whether these structures cause the disease or whether they are a by-product of it. It’s a chicken-or-the-egg problem.

Though we don’t know what causes Alzheimer’s, there is probably no single factor that explains why we get the disease. The greatest known risk factor is increasing age. The likelihood of developing Alzheimer’s almost doubles every five years after age 65, until the age of 85, when the risk reaches nearly 50 percent.

Family history is another risk factor, especially in families where individuals come down with the disease early in life. Those who have a parent or sibling with Alzheimer’s are two to three times more likely to develop the disease than those who do not. Scientists have also found one gene that increases the risk of Alzheimer’s, though having that gene does not guarantee an individual will develop the disease.

The changes in the brains of people with Alzheimer’s probably begin 10 to 20 years before any symptoms appear. At first, a person with Alzheimer’s will get confused, tend to forget things, and be unable to resolve simple math problems. As the disease progresses, the symptoms become more noticeable. People in the middle stages of Alzheimer’s will forget to do the simple things in life like taking a bath, combing their hair, cleaning their teeth. They will fail to recognize familiar places, their surroundings, and their families. As they lose touch with what is going on, they become frightened, anxious, and aggressive.

Eventually most of these patients need complete care. The average time from onset of the symptoms to total disruption of daily function is about eight to ten years. Some people manage to live with Alzheimer’s for up to 20 years.

The only way to definitively diagnose Alzheimer’s is postmortem, through an autopsy. Because there are so many other diseases that can mimic this illness, it’s very important when Alzheimer’s is suspected to find a doctor who is able to distinguish between Alzheimer’s and some other forms of dementia. The right doctor will know how to use a variety of neurological imaging devices to look for and pinpoint the plaques that are characteristic of Alzheimer’s and measure the progression of disease.

At present there’s no treatment whatsoever for Alzheimer’s. Drugs like Cognex or Aricept may be given in the early to early-middle stages of the disease to alleviate the symptoms and reduce the sufferer’s agitation, lack of sleep, and depression. At the very least, the drugs make the scenario easier to deal with for the caregiver. Since the plaques may be creating an inflammatory response in the surrounding brain tissue, nonsteroidal anti-inflammatory medicines such as ibuprofen have been shown to help slow the progress of Alzheimer’s disease.

Some reports suggest that the use of antioxidants like vitamin E and vitamin C can also slow the disease, while ginkgo biloba supplements seem to improve cognitive functioning, but there’s really no evidence that such vitamins and supplements are truly effective. Since the way the brain degenerates in Alzheimer’s disease somewhat resembles the way in which the brain is affected in diabetes, some treatments for Alzheimer’s patients concentrate on improving their diet, and the recommended diet is one that’s rich in vegetables and low in fat.

The problem with Alzheimer’s, aside from being one of the most difficult diseases that anybody can have, is that it not only affects the individual but, as with stroke patients, it affects the physical and mental health of the victim’s entire family. Families and spouses end up having to provide day-to-day care for these people, and it’s often very difficult to do so. The Alzheimer’s Association, with its multiple chapters around the country, does the best it can to provide support and information to families with an Alzheimer’s sufferer.

Click here to check out Dr. Manny's book The Check List (Harper Collins, 2007), from which this article was excerpted.

Dr. Manny Alvarez is the managing editor of health news at FOXNews.com, and is a regular medical contributor on the FOX News Channel. He is chairman of the Department of Obstetrics and Gynecology and Reproductive Science at Hackensack University Medical Center in New Jersey. Additionally, Alvarez is Adjunct Professor of Obstetrics and Gynecology at New York University School of Medicine in New York City.

Dr. Manny Alvarez serves as Fox News Channel's senior managing health editor. He also serves as chairman of the department of obstetrics/gynecology and reproductive science at Hackensack University Medical Center in New Jersey. Click here for more information on Dr. Manny's work with Hackensack University Medical Center. Visit AskDrManny.com for more.