Dear Doctor: What’s all this I'm hearing about Parkinson’s disease having something to do with the gut? I thought it was about the nervous system and the brain.

Dear Reader: You’ve zeroed in on an intriguing area of inquiry into Parkinson’s disease in which new information emerges seemingly every week. With each new link between Parkinson’s and the gastrointestinal tract, researchers edge closer to uncovering the causes of the disease, as well as identifying novel avenues of treatment.

It’s estimated that more than a million people are living with Parkinson’s disease in the United States, and about 60,000 new cases get diagnosed each year. Symptoms typically arise in people age 50 and older, and with millions of baby boomers reaching that threshold, the need for effective treatments is ever more pressing.

Parkinson’s is a progressive disease of the nervous system in which nerve cells and certain other structures deep within the brain begin to deteriorate for reasons that are not yet fully understood. This leads to a deficit of dopamine, a neurotransmitter that sends signals to nerve cells and helps us achieve smooth and deliberate movement. The symptoms of Parkinson’s -- including tremors, rigidity, problems with gait and a general slowing of movement -- arise from these and other changes. As a result, much of the research into Parkinson’s disease has focused on the brain and nervous system.

In recent years, however, scientists have begun to turn their attention to something known as the gut-brain axis. This is a term for the variety of ways in which the gut communicates with the brain, including via the nervous system and the endocrine system, and signaling mechanisms built into the immune system. Among the factors that influence these communications are the trillions of microorganisms that live within our intestinal tract. This has led scientists to explore how the microbiome may play a role in neurodegenerative diseases, including Parkinson’s, and how it might be harnessed in treatments -- or even a cure.

One study followed a group of patients who underwent a procedure that removes portions of the vagus nerve, which runs throughout the body and links the brain and the gut. Five years after the surgery, these patients were found to have a 40% lower incidence of Parkinson’s disease than those whose vagus nerve remained intact.

In another study, conducted in mice bred to be susceptible to Parkinson’s disease, researchers saw a surge in Parkinson’s symptoms when the mice were implanted with fecal samples from Parkinson’s patients. This didn’t happen in the mice implanted with fecal samples from healthy adults.

Previous research has found that the same abnormal protein clumps that form in the brains of patients with Parkinson’s disease are also present in the gut. And from the time that Dr. James Parkinson first identified the disease in 1817, health care professionals have noted that symptoms like constipation and gastrointestinal distress often develop in the years prior to neurological symptoms. All of this has led to increasing speculation that Parkinson’s disease originates in the gut and spreads to the brain, and has set the stage for exploring gut-based therapies and a potential cure.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: A dear friend is about to start chemotherapy treatments, so I've been researching the side effects she can expect, and it’s a lot. I’ve read that even her sense of taste could change. Is that true? Can anything be done?

Dear Reader: You’re correct about the wide range of potential side effects that can occur during treatment for cancer. Although we tend to be most familiar with the nausea, hair loss and fatigue that often accompany chemotherapy, adverse side effects can arise from many different cancer treatments.

In addition to chemotherapy, treatments include radiation, hormone, precision and immunotherapies. In the course of targeting and disrupting cancer cells, these therapies can result in swelling, bruising, anemia, infection, nerve pain, memory problems, urinary and bladder issues, diarrhea, loss of appetite and as you have discovered, changes to the sense of taste. The sense of smell, which is closely linked to our ability to taste, can be affected as well.

A loss of appetite and changes to taste may seem like the least challenging side effects in that daunting list, but they can have a profound effect on a patient’s ability to both withstand the rigors of treatment, and to their successful recovery once treatment has concluded.

Due to physical side effects like nausea, pain and fatigue, patients often lose their appetites. This makes proper nutrition and maintaining weight a common struggle for cancer patients. Add in an altered sense of smell and taste, and the goal of a nourishing diet becomes even more of a struggle. That’s why we think it’s wise for patients to work with a registered dietitian to help with specific nutritional needs during treatment, and during recovery as well.

Changes to taste often accompany certain cancer medications, which can alter the communication between the brain, which interprets taste and smell, and the receptors in the mouth and nose. Dry mouth, mouth infections and sores in the mouth and gums can also affect taste. Patients often report that foods take on a metallic taste, or come across as acidic, bitter or even rancid.

Though these changes can’t be reversed during treatment, there are strategies to help patients manage them. Patients who find that certain foods taste bad, even those that were previous favorites, shouldn’t force themselves to eat. Instead, experiment with small amounts of other foods to find something more tolerable, even if they’re odd or unfamiliar. Foods served at room temperature or chilled will often carry less scent and flavor than those that are hot. Fresh and frozen fruit and vegetables won’t carry the same tinny taste of canned foods.

The American Cancer Society suggests rinsing the mouth with a solution of 1/2 teaspoon of salt and 1/2 teaspoon of baking soda, mixed into a cup of warm water, to help stop bad tastes. It’s also important to practice good oral hygiene, brushing several times each day and flossing. We’re happy we can end with the good news that, for most patients, taste and smell return to normal in a few months following the end of treatment.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: One of the yoga teachers at our gym always goes on and on about the importance of the vagus nerve whenever we do deep-breathing exercises to relax. What is she talking about, and why is it important?

Dear Reader: Your yoga instructor is referring to one of the attributes of the ever-fascinating vagus nerve, which is the most complex of the 12 cranial nerves. Like each of the cranial nerves, the vagus nerve arises directly from the brain rather than the spinal cord. It’s the longest of these nerves, and it travels a meandering path through the body, beginning in the brain, through the face, neck and upper body, and to the abdomen, where it ends in the colon. In fact, its name derives from the Latin word for "wandering."

Along the way, the vagus nerve divides, branches out and exchanges fibers with numerous other nerves, thus playing a role in an impressive array of our sensory and motor functions. It’s one of the crucial links between the brain and the neck, lungs, heart and abdomen, and it helps to regulate mood, heart rate, digestion, anti-inflammatory and immune response. The gut and brain communicate via the vagus nerve, as do many other parts of the body.

There’s so much to tell about this remarkable structure that we could easily fill several columns and not scratch the surface. So let’s get right to your question about the vagus nerve and deep breathing.

One of the functions of the vagus nerve is to communicate with the diaphragm. That means that when you’re taking the slow, deep and controlled breaths associated with yoga, which engage the muscles of the abdomen and the diaphragm, you’re stimulating the vagus nerve. And since vagal stimulation has been found to help lift mood, lessen anxiety and even lower blood pressure, it follows that you can trigger this relax-and-restore response by doing some deep breathing exercises.

What’s great about diaphragmatic deep breathing is that it’s portable. You can do it anywhere, at any time, without any special equipment. And the bonus is that you can practice it in public without anyone knowing you’re doing it. If you have a home-based blood pressure device, you can do your own experiment about the benefits. Start by taking a baseline blood pressure reading without any special preparation. Follow this with a few minutes of diaphragmatic breathing. For anyone who has never tried it, it’s slow, deep breaths that fill the lungs from bottom to top. Be sure to relax and soften the muscles of the belly, which will pop out a bit as you breathe, to get the full beneficial effect.

Holding the breath for five to 10 seconds also stimulates the vagus nerve. So does adding a bit of resistance to the exhale, which can be achieved by blowing out through pursed lips. Not only do these breathing techniques have the potential to impart a sense of calm and relaxation, they quiet the fight-or-flight response in our bodies. And as you’ll see if you try the blood pressure monitor experiment, they will often yield a lower blood pressure reading.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)