Dear Doctor: I’ve been taking biotin for my nails, but I’ve read that it can mess up the results of important lab tests. Should I stop taking it?

Dear Reader: Biotin is one of the eight B vitamins, each of which plays an essential role in cell function. Also known as vitamin B7, biotin helps the body break down and absorb fatty acids, glucose and amino acids. (Basically, energy production.) It’s also important in DNA repair, gene regulation and cell signaling.

Biotin is a water-soluble vitamin, which means it’s not stored in the body. However, it’s naturally available in a wide range of foods, including eggs, beef, dairy products, sunflower seeds, pork, salmon, brewer’s and nutritional yeast and organ meats. It’s also found in certain vegetables, including spinach, broccoli, cauliflower and sweet potatoes.

Although a minimum recommended daily requirement (RDA) for biotin has not been established, the National Academy of Sciences’ Food and Nutrition Board suggests adults get at least 30 micrograms of biotin per day, and that women who are breastfeeding aim for a minimum of 35 micrograms per day. A balanced and varied diet will naturally provide enough biotin.

Symptoms of a biotin deficiency include hair loss, brittle nails and skin rashes, which has led biotin supplements to be promoted for improved hair growth, stronger nails and better skin. The vitamin is used in veterinary medicine, where it has been shown to help heal the cracked hoofs of pigs and horses.

When it comes to human applications, only a few small studies have been done. In 1989, researchers found that 41 of the 45 women who completed a biotin study showed measurable improvement to the strength and firmness of their fingernails after taking 2.5 milligrams of the vitamin for about six months. Most of the positive reports about the effects of biotin are anecdotal.

Unfortunately, as you point out, biotin supplements can have grave and unintended consequences in lab tests. The biotin our bodies need is measured in micrograms. But the amount of biotin in many supplements comes in milligrams, in quantities that can be up to 650 times the RDA. High doses of the supplement can cause a range of lab tests, including one used to diagnose heart attack, to yield skewed results. This happens because certain lab tests use biotin as part of the testing method. Patients taking biotin supplements can get lab results that are too high or too low, which puts them at risk of being misdiagnosed or not receiving the proper treatment. In one case, a patient died because his biotin intake obscured the test results that would have shown he was having a heart attack.

Biotin is now added to so many multivitamins and supplements that you may be ingesting large amounts without even realizing it. People who take a biotin supplement should disclose this fact to their health care provider before undergoing tests. If you’re not sure, carefully read the labels of any supplements, particularly those marketed to help with nails, hair or skin. Because biotin is water-soluble, it takes just a few days to clear it from the body and thus be ready for accurate lab results.

(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: 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.)