Dear Doctor: I am a 60-year-old man who exercises regularly and takes no medicines. At my last physical exam, my doctor gave me an advance directive form. Do I really need to fill one out?

Dear Reader: Unequivocally, yes. Advance directives are forms providing direction to both family members and the medical community about your wishes in emergencies. More to the point, they specify what your wishes are, in case you can't speak for yourself.

The first part of an advance directive asks whom you would want to make medical decisions for you. Termed a medical power of attorney, this can be your wife, one of your children or a very good friend. It cannot be your doctor. The crucial aspect of this choice is the level of trust you have in your decision maker. If you were to lose decision-making capacity, this person would speak with doctors about your care on your behalf -- becoming both your advocate and the person who chooses resuscitative measures, if any. Not only should you trust the person to whom you give medical power of attorney, you also need to have frank conversations with that person about what you would want.

It sounds as if you're healthy, and thus have a low likelihood of a major illness. But health problems can happen at any time. If you were hospitalized for a heart attack, stroke or a traumatic brain injury, what choices would you want to make? If you were unable to breathe, would you want a tube, attached to a ventilator, placed into your lungs? The answer may be yes -- but not indefinitely. If that's the case, then for how long? Would you consider a tracheostomy, if you were on a ventilator for more than two weeks? Again, the answer may be yes. How about a feeding tube that enters your stomach through your skin? For how long would you want such a measure?

These are not easy topics to consider, or to discuss with the ones you love. But they are important. Ideally, doctors could help with the discussion about end of life, but because the nature of doctors is to treat and heal, many have difficulty discussing end-of-life decisions with their patients. Studies have shown that even with patients who face a life-limiting disease, physicians discuss advance directives only 40 to 45 percent of the time.

One study posed a hypothetical situation in which a man with stage 4 gastric cancer, metastasized to his lung, comes to the emergency room with his wife for severe shortness of breath. The husband and wife in this scenario did not have an advance directive, but their preference was for the husband to remain comfortable and out of the intensive care unit. Only 48 percent of the 27 physicians who treated this hypothetical patient were able to coax out the appropriate information in order to treat him in accordance with his goals and preferences.

Now, I know you don't have gastric cancer, but death is an inevitability. Providing your loved ones, the medical system and yourself direction about your course of care gives you some control over that inevitability.

(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: My dad has just been diagnosed with vascular dementia. What is it? Can it be prevented?

Dear Reader: Dementia is a general term used to categorize symptoms that relate to the decline or loss of cognitive function. These include confusion, memory loss, impaired language skills, changes in personality or behavior, and the inability to think clearly or perform everyday tasks. The most common cause of dementia is Alzheimer's disease, which accounts for between 60 and 80 percent of all dementia cases. The mental impairment of Alzheimer's disease results from a series of complex changes that take place within the structure of the brain itself.

Vascular dementia, which is also called vascular cognitive impairment, causes the majority of non-Alzheimer's cases of dementia. It occurs when the blood vessels in the body, known as the vascular system, become blocked, diseased or damaged and are unable to provide the brain with normal blood flow. This deprives the brain of adequate oxygen and nutrition, which causes brain cells to die. The resulting injury, which prevents different parts of the brain from communicating with one another, causes symptoms of dementia.

Hardening and narrowing of the arteries, a major stroke or a series of small strokes can cause vascular dementia. In the case of major stroke, symptoms of vascular dementia can appear suddenly. But quite often, the disease builds slowly. As blood flow to the brain decreases, mental impairment gradually becomes more pronounced.

At this time, vascular dementia cannot be reversed, but there are steps you can take to reduce your risk of developing it. Although the disease is rare before age 65, the cardiovascular problems that lead to it can begin to develop well before then.

One of the major risk factors for vascular dementia is high blood pressure, which also plays a role in heart attack and stroke. That's why it's important to know your numbers, and to monitor blood pressure on a regular basis.

To reduce blood pressure, maintain a healthy weight. It's wise to also keep track of your waistline measurements. Men who measure more than 40 inches at the waist and women whose waistlines measure more than 35 inches are at increased risk of developing high blood pressure.

Get moving. Regular exercise has been shown to reduce the risk of vascular dementia by 40 percent. Just 30 minutes of exercise at moderate intensity -- you'll be able to speak but not sing -- three times per week helps protect both your heart and your brain.

If you've been following this column for even a few weeks you know what's coming next -- don't smoke. If you do smoke, please stop. Yes, we know that's hard. We also know that your family doctor would love to help you.

Eat a healthy diet: lean meats, fresh fish, legumes, whole grains, seeds, nuts, and plenty of fruits and vegetables. Skip the sugar if you can. Limit simple carbs like pasta, rice, bread and processed cereals.

Limit how much alcohol you drink. Even in moderation, alcohol has been linked to dementia risk, particularly as we get older.

(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: I love ham sandwiches -- and have one almost every day. I also have asthma, and just read that processed meats can increase the risk of asthma. How can this be?

Dear Reader: Meats have been cured -- that is, preserved and flavored -- since ancient times, largely through salting or smoking. Potassium nitrate and sodium nitrite salts were used to some degree in the Middle Ages, though the practice was not widespread. In the United States, these salts have been used to cure meat since 1925, and are highly effective in decreasing the incidence of bacterial disease. However, ingested nitrates and nitrites can form nitrosamines, which are carcinogenic.

Now comes a study, published last year in the journal Thorax, concluding that cured meats like ham increase the risk of asthma. The study enrolled 971 male and female participants from five cities in France. The enrollees -- not all of whom had asthma -- filled out a 118-item food-frequency questionnaire. Cured items included ham, sausage and dried sausage. Exposure was categorized as less than 1 serving a week; 1 to 3 servings per week; or greater than 4 servings per week. Participants reported the severity of their asthma over a 12-month period and scored this from 0 to 5, with 5 being waking up from sleep with an asthma attack.

At the beginning of the study, those who consumed more than 4 servings of cured meat per week were more likely to be men, were slightly more likely to smoke, were slightly more obese and had slightly lower educational levels. Those who ate more than 4 servings per week of cured meat were also more likely to be asthmatic and have more severe asthma at the beginning of the study.

After seven years, the participants filled out another survey regarding their level of asthma. Among those who ate less than 1 serving of cured meat per week, 14 percent reported increased asthma symptoms; among those who ate more than 4 servings of cured meat per week, 22 percent reported increased asthma symptoms. Noting that increased weight is also a factor for worsening asthma symptoms, the researchers adjusted for weight, smoking and educational levels -- and still found a correlation between worsening asthma and cured meat.

Oddly enough, two U.S studies have found that people newly diagnosed with chronic obstructive pulmonary disease were more likely to eat cured meats four to six times per week, but they did not find an increase in asthma risk. The cured meats here also included hot dogs and bacon.

As for why eating cured meat might worsen asthma, theoretically, nitrites can cause oxidative stress within the lungs and lead to more inflammation within the body, which can worsen asthma. While nitrates and nitrites may worsen asthma, I am not certain that they create asthma.

In addition, these studies did not separate meats cured by nitrites or nitrates and those cured by other means.

The take-home message: Stay away from meats cured with sodium nitrite or potassium nitrate. Not only are cured meats associated with greater obesity and increased asthma, meats cured with nitrites and nitrates increase the risk of cancer. If you don't have asthma and you don't smoke cigarettes, cured meats without nitrites and nitrates should be safe, but still, it's better to limit them. When you're shopping for smoked meats, make a close read of the food labels part of your pre-purchase routine.

(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.)