Dear Doctor: My husband and I have been reading about a possible connection between aluminum and Alzheimer's disease. Some reports even discourage the use of aluminum foil for cooking. Is there a connection between aluminum and Alzheimer's?

Dear Reader: Your worries center around the most-abundant metal and the third-most abundant element, one that by mass makes up 8 percent of the Earth's crust. Plants and animals have evolved in an environment in which aluminum is common. In fact, aluminum is even present in the human brain. This most fundamental of organs contains, on average, 1.02 micrograms of aluminum per gram of brain tissue. Further, brain levels of aluminum increase with age, causing researchers to take a look at how that happens -- and what might be the result.

The human body absorbs aluminum from compounds in water, food, aluminum-based utensils, deodorants and drugs. But at toxic levels, aluminum can damage neurons in the brain as well as DNA within neurons. The aluminum ion can affect normal cellular reactions in the brain, cause brain inflammation and lead to neurofibrillary tangles and amyloid deposits that are the hallmark of Alzheimer's disease. In fact, aluminum chloride in combination with the sugar D-galactose injected in rats and mice induces many of the brain changes and behavioral changes seen in Alzheimer's disease.

In one important study, researchers studied the postmortem brains of 12 people with familial Alzheimer's disease in England. They found elevated aluminum content in all but one of the brain samples. The researchers also found aluminum concentrated near neurofibrillary tangles and amyloid deposits, which have been linked to Alzheimer's. They couldn't conclude that aluminum was the cause of the dementia; it may be that degenerative brain diseases concentrate and retain aluminum within the brain. Still, a connection seems clear.

The findings are alarming. Aluminum is more ubiquitous today than ever before. Aluminum hydroxide, aluminum sulfate and aluminum chloride are used in drinking water treatment and waste water management, and we use aluminum foil and aluminum in our food preparation and storage. Considering such exposure, it's important to ask questions about the potential impact.

A 15-year study in France assessed the aluminum levels in drinking water and the rate of Alzheimer's disease in multiple areas of southern France. The concentration of aluminum in the water varied from 0.001 to 0.514 mg/liter depending on location. Of the 1,677 people over the age of 65 who completed the study, 461 were diagnosed with dementia. Those whose aluminum intake was more than 0.1 mg per day had 2.26 times the risk of dementia compared with those whose intake was less than 0.1 mg per day.

All of that said, neither I nor medical science overall can provide a hard and fast answer to your question about the risk of aluminum exposure. It is heartening, however, to know that water boards measure the amount of aluminum in drinking water at a time when the correlation between human exposure to high levels of aluminum and dementia is still largely unknown.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: What's the difference between probiotics and prebiotics? I'm really interested in how gut bacteria impact health, but I'm not sure I always understand the terminology.

Dear Reader: We agree with you that the information emerging about gut bacteria is fascinating. And as with any area of research, the language used to discuss it can be confusing.

Probiotics are live microorganisms that are meant to have health benefits for the person who ingests them. They work by joining the many trillions of bacteria already living within our bodies, primarily in the gut. Collectively known as the human microbiome, these beneficial strains of bacteria harbor a diversity of genes that dwarfs that of the human genome.

Thanks to the rapid evolution of genetic sequence technology, researchers are learning new information about the human microbiome every day. Thus far, probiotics show promise in the areas of immune function and various digestive and bowel disorders. Probiotics have also been used to help preterm infants acquire a beneficial range of intestinal flora, which can prevent colonization by adverse bacteria.

You can ingest probiotics in food or in supplement form. When it comes to food-based probiotics, the common denominator is fermentation. Foods like yogurt, kefir, apple cider vinegar, pickles, kombucha, sauerkraut, kimchee, miso and certain soft cheeses are all sources of different types and varying amounts of probiotics.

The idea is that by ingesting these microorganisms, the portion of them that survive the acids of the stomach will take up residence in the gut. Once there, though, they need their own food source to grow and thrive. And that's where prebiotics come in.

Prebiotics are indigestible carbohydrates that act as food for probiotics. While some foods offer a greater percentage of prebiotic material than others, when you eat a diet high in a variety of vegetables, fruit and leafy greens, you are inevitably giving your gut bacteria plenty to eat.

You'll find a motherlode of prebiotics in foods like leeks, asparagus, Jerusalem artichokes, bananas, onions, garlic, artichokes, jicama and honey. Also beneficial is something known as "resistant starch," which is the indigestible portion of starch. It can't be broken down by the small intestine, so it moves to the colon, where it is fermented by the microbiota.

Whole cereal grains, many seeds and green bananas are good sources of resistant starch. So are cooked potatoes and rice, but only when they have cooled. Just as with probiotics, you can go the supplement route for prebiotics if you choose.

If you decide you'd like to add probiotic supplements to your diet, we suggest you check with your family doctor for guidance. Although regulated by the FDA, probiotic supplements are treated as a food and not a medication. That means that manufacturers don't have the burden of proof that their products will live up to the claims printed on the label. Your doctor can help you figure out which supplements to choose, and the best dose for you to start with.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: What can be done for normal pressure hydrocephalus? My dad was diagnosed with this condition six months ago after developing severe gait problems, urinary urgency and memory issues. He has a few other physical issues, but is otherwise healthy.

Dear Reader: I'm glad your father's doctor was able to pinpoint the source of his symptoms. Because normal pressure hydrocephalus (NPH) is a rare condition, with a gradual onset of symptoms, it can be difficult to diagnose. The annual incidence is between 1.19 and 3.4 per 100,000 people. This form of hydrocephalus, or "water on the brain," can occur after a head trauma, stroke or brain tumor, but in some cases, the cause is unknown. To understand the condition takes an understanding of the fluid that bathes the entire brain and that flows through its ventricles, or cavities.

This fluid, called cerebrospinal fluid, is produced by the lateral ventricles of the brain and is eventually reabsorbed into the body through veins within the brain. If the body has difficulty reabsorbing the fluid, the fluid increases within the ventricles, putting pressure on the brain itself. This pressure damages the nerves and nerve connections within the brain. Initial symptoms include difficulty walking, as if a person's feet are glued to the floor, and with the feet outwardly rotated. Patients also have difficulty turning and can lose stability and fall.

People with the condition also have concentration problems, slowed mental abilities and a lack of concern for their disability. Lastly, they have urinary urgency, which can lead to urinary incontinence.

Once you have a diagnosis, however, you can move to treatment, which consists of decreasing the level of cerebrospinal fluid within the skull.

This is done through a ventriculoperitoneal (VP) shunt. After drilling a small hole in the skull, a neurosurgeon places a catheter into the lateral ventricle within the brain. That catheter is attached to a valve behind the ear. From the valve, another catheter is guided down the neck and into either the chest or abdomen. When the pressure builds in the ventricle, the valve opens, draining the fluid from the brain into the chest or abdomen, depending where the second catheter ends. This fluid is then reabsorbed by the body.

The effectiveness of shunts varies widely, studies suggest. The greatest patient improvements seem to be in the ability to get up out of a chair and walk. Memory and reaction time also can improve after shunting, as can urinary symptoms. However, if memory deficits are to the point of moderate to severe dementia, then a shunt may not help that aspect.

One important thing to note is that the longer the patient has symptoms, the less likely a shunt will provide benefit. This is especially true if symptoms have been present for more than two years.

VP shunts can have many complications, including a risk of bleeding, brain infections, seizures, malfunction of the shunt or an over-drainage of cerebrospinal fluid. The rates of these complications are decreasing, but still can occur up to a third of the time.

Based on what you've told me, the cause of your father's hydrocephalus is unclear. Nonetheless, if the shunt is stable, patients like your father can have sustained benefit for many years.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)