Dear Doctors: A friend of mine was recently diagnosed with Parkinson's disease. She has been told that exercise -- especially swimming -- can be helpful. She isn't a strong swimmer and is afraid to try now. Why are people with Parkinson's advised to swim? Are there any drawbacks?

Dear Reader: Parkinson's is a progressive neurological disease that causes changes to the centers of the brain that control movement. These lead to decreased production of a neurotransmitter known as dopamine, which is crucial to our ability to generate smooth and sustained movement. Over time, Parkinson's interferes with walking, balance, strength, endurance and coordination. It can also adversely affect mood, emotions, sleep and cognition.

There is no cure for Parkinson's disease at this time. But certain medications, and combinations of medications, can help to manage symptoms.

Your friend is correct about exercise being an important element in managing the symptoms of Parkinson's disease. A body of research has shown that regular exercise can help maintain balance and mobility, improve posture, enhance mood and aid in the performance of daily tasks. Some studies suggest that exercise can sometimes play a role in slowing disease progression.

A well-rounded exercise program includes strength training, aerobic activity and stretching. Among the options are aquatic exercises. And while this category of exercise does include swimming, it also extends beyond that. As the popularity of water aerobics, Zumba, pool walking and pool running have shown, virtually any upright exercise can be transferred to water. That means your friend can get the benefits of exercising in water without swimming.

Water offers two important benefits to patients with Parkinson's. One is buoyancy. It eases the force of gravity, which in turn eases stress on the joints. Buoyance also helps to support balance, which can lessen the risk -- and the fear -- of falling. The other benefit is the resistance that occurs when moving in or through water. Simply walking through water causes the muscles to engage and do gentle but sustained work. This combination of resistance and buoyancy creates a kind of safety net that allows someone to safely try larger and more sustained movements. These can help to build strength and maintain flexibility.

In asking about drawbacks to water exercise, you have broached an important topic. Anyone with movement limitations, including patients with Parkinson's, should never be in a pool alone. Due to the progressive nature of the disease, which includes a decrease in coordination, patients with Parkinson's are at increased risk of drowning. This is particularly true of swimming, which requires different but coordinated actions by the legs and arms.

People with Parkinson's often develop difficulty in the regulation of body temperature. That makes it important to consider water temperature when performing aquatic activities, both in outdoor and indoor settings.

If your friend decides to try aquatic activities, she should begin by checking in with her medical care team. They will advise her about the level of activity that is appropriate for her specific condition. They can also refer her to specialized classes, or to a physical therapist experienced in working with patients with Parkinson's.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Hello, dear readers, and welcome to a bonus edition of our monthly letters column. Our mailboxes are overflowing, so we'll get right down to business.

-- We recently wrote about living organ donation. That's when a living person gives an organ, such as a kidney, or part of an organ, such as the liver, to another individual. The column led to a question from a reader in Pennsylvania: "Is there a minimum GFR to become a kidney donor?" she asked. "I recently filled out a registry form for a specific patient but forgot to ask about this."

GFR stands for “glomerular filtration rate.” It indicates how well someone's kidneys are working. The result of a GFR test is used to help evaluate if donating a kidney might put someone at long-term risk. The answer to the question is a bit complicated. That's because the minimum GFR to become a kidney donor depends on the person's age and on other health considerations. Also, each transplant center has its own donor guidelines. If your registry moves forward, the transplant center will let you know its requirements. No matter the outcome, filling out the registry is a generous act.

-- A column about a very small clinical trial into a new treatment for lupus, which is an autoimmune disease, brought this question from a reader: "I was recently diagnosed by my rheumatologist with lupus," they wrote. "Having read your column, I wanted to learn the current status of this new treatment. My doctor said it is still in the investigative stage."

The treatment, known as CAR T-cell therapy, harnesses the immune system to fight disease. It is sometimes used to treat certain blood cancers. At the end of the clinical trial we wrote about, the five lupus patients were considered to be in remission. Your doctor is correct that this therapy for use in lupus is still in the investigative stage. However, there is encouraging news. Last May, the FDA fast-tracked a second clinical trial. This not only speeds up the development and review of a potential new lupus therapy, but it also makes it eligible for accelerated approval.

-- We received a letter from a reader who had asked us about diverticulitis, a condition in which small bulges in the lining of colon become inflamed. "I've been managing my condition very well with eating more fermented foods, such as pickles, sauerkraut and yogurt, as well as drinking kombucha and kefir," they wrote. "Taking probiotics has also helped. Are they being evaluated as an aid for diverticulitis?" We're very glad to know the information in the column was helpful to you. As for the potential use of probiotics for this condition, you'll be happy to learn that this is, indeed, a subject of study.

Thank you, as always, for all of your letters. We love hearing from you. A reminder that, due to the general nature of this column, we are unable to review personal medical data, lab test results, scans or photographs. We also can't offer a diagnosis, provide a second opinion, evaluate medications or offer a specific treatment plan.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctors: I had a scare exercising on a hot day. I got a terrible headache, my skin got clammy and I felt really weak. I was sure I was going to faint. I had to get into a cool bath to start feeling better. I drank plenty of water and was sweating a lot. Shouldn't that have protected me?

Dear Reader: You have described the symptoms of heat exhaustion. It's a heat-related illness on a spectrum that ranges from unpleasant to life-threatening. These illnesses occur when the body begins to exceed the fairly narrow span of core temperature of 97 to 99 degrees Fahrenheit that it needs to function properly.

When you begin to overheat, your body takes immediate steps to counteract it. The first is cooling the blood by sending it to the surface of the skin. It causes the reddened flush we get during exercise. This is accompanied by sweating, which provides surface moisture for an evaporative effect. When these are insufficient, core body temperature will begin to rise. That's when heat illness sets in.

Known as hyperthermia, heat illnesses are a serious health threat. On the milder side are heat cramps. These are painful muscle spasms that can occur during or after strenuous exercise in hot weather. While not an immediate threat to health, they can be a warning sign of heat exhaustion.

In heat exhaustion, core body temperature begins to rise. In addition to resting and gradually rehydrating, it's important to cool the skin to reverse the effects of excessive heat. This can be done with a bath or shower, or by spraying or sponging the skin with cool water.

If left untreated, heat exhaustion will progress to heat stroke. This is a medical emergency. Without immediate medical intervention, heat stroke can cause permanent disability, and potentially lead to death. Heat stroke occurs when the body loses all control over maintaining core temperature. The symptoms are similar to those of heat exhaustion. However, in heat stroke, the body stops producing sweat. Skin becomes dry, red and hot to the touch. Someone with heat stroke will also have a rapid and pounding pulse, confusion and eventually lose consciousness.

You're correct that drinking plenty of water, which the body needs to produce sweat, is crucial to preventing heat-related illnesses. However, sometimes it's not enough. In areas of high humidity, sweat evaporates far more slowly, if at all. This cancels out the body's primary cooling mechanism. Exercise is another factor. The action of our muscles generates a large amount of heat. When exercising in hot weather, it's possible to raise core body temperature to dangerous levels. This is known as exercise-induced hyperthermia.

To stay safe, exercise early in the day, when it's cooler. Spend the heat of the day in a cool place. If your home is inadequate in this regard, use public spaces, such as malls, public libraries and senior citizen centers, which are air-conditioned. Many communities open dedicated cooling centers during a heat wave. We have experienced extended heat waves all over the United States this summer. Please take the potential threat of these hot days seriously.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)