Dear Doctor: What's with all the ads for brain-enhancing products? Prevagen is one that claims it’s been clinically proven to help, but my family doctor says that it hasn’t. Who’s right? Do these products actually help with memory issues?

Dear Reader: More than one-third of the United States population is now aged 50 and older, a time of life when people start noticing changes to memory and the ability to learn. With each momentary lapse -- fumbling for a word or forgetting a name -- people are reminded of their aging brains. It’s not surprising that a multibillion-dollar industry in brain health supplements has sprung up.

These products promise not only to preserve and enhance memory, but to sharpen focus, boost attention spans, lift moods and increase creativity. Supplements marketed as brain boosters typically include omega-3 fatty acids, certain B vitamins, vitamin E, ginseng and ginkgo biloba extract. However, despite decades of study into whether these substances actually work to preserve or enhance brain health and functioning, the research remains inconclusive.

When it comes to Prevagen, a memory supplement derived from jellyfish, the parent company’s advertising claims led the Federal Trade Commission to charge it with fraud in early 2017. That legal battle is ongoing. Meanwhile, since the product is marketed as a supplement, it doesn’t have to undergo Food and Drug Administration testing for safety or review for efficacy. It’s also free from a range of FDA scrutiny and oversight.

You’re correct that the company’s marketing cites positive results from a clinical study. But critics point out that these claims arise from selective use of data drawn from a single study, which was carried out in-house by the parent company of the product. In that study, the product and a placebo were found to be equally effective.

Until the day that science develops a real brain pill, we advise our patients to preserve their cognitive health the old-fashioned way. That is, eat right, control blood pressure, get enough sleep and exercise regularly. A diet that focuses on fresh fruits and vegetables, lean meat, fish, whole grains, legumes and healthful fats has been shown to reduce the risk of chronic disease, including heart disease. That’s important because heart disease, as well as uncontrolled high blood pressure, have been linked to cognitive impairment later in life.

Research has also repeatedly drawn a connection between regular exercise and cognition. Not only does a mix of aerobic exercise, weight training and stretching improve strength, balance, endurance and mood, it has been shown to help the brain maintain existing neural connections, and to build new ones. With just 30 minutes of moderate exercise each day, you’ll exceed the federal guidelines for adults, which recommend about 150 minutes per week.

One final piece of the cognitive health puzzle is ongoing social interaction. Recent research suggests that adults who have regular contact with other people have better memory and preserve their cognitive abilities to a greater degree than do adults who are solitary.

(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: I just turned 55 and have noticed that I get winded faster these days when I go running. Does getting older affect how much air your lungs can hold? Is there any way to increase it?

Dear Reader: Yes, aging does have an effect on our lungs and how they function. In fact, the decrease in capacity begins about a decade after our lungs become fully mature, which is in our early- to mid-20s.

Your question addresses something known as tidal volume, which is the amount of air that moves into and out of our lungs with each breath. For healthy adult women, tidal volume is about 0.4 liters. For men, it’s about 0.5 liters. However, the volume of each breath is one of several variables that affect breathing function.

In addition to the lungs, the respiratory system includes the diaphragm, the dome-shaped muscle that separates the chest cavity from the abdomen; it also includes the ribs, sternum and supporting muscles and soft tissues, also referred to as the thoracic cage. Each of these plays an important role in breathing. The lungs hold the air, the motion of the diaphragm causes the lungs to fill and empty, and the thoracic cage provides support and protection.

As we age, the respiratory system undergoes gradual changes that affect its structure, physiology and immune function. Injury, poor posture, osteoporosis and the natural shrinkage of bones, muscles and soft tissues all contribute to a decrease in the size of the thoracic cage. This, in turn, has an effect on maximum air volume. A decrease in the strength of the diaphragm also affects how much air can be drawn into (and out of) the lungs. The lungs themselves lose elasticity with age, and the millions of tiny air sacs that they contain, known as alveoli, can lose shape and become “baggy.” Smoking and exposure to air pollution contribute to a decline in lung function. So do repeated respiratory illnesses, another reason to stay current with flu and other vaccinations.

The good news is that regular exercise can help to maintain lung function and tidal volume. Aerobic exercise is a great way to keep your lungs fit. Resistance training that targets the chest, shoulders and back muscles helps maintain strength and flexibility of the diaphragm and the thoracic cage. Breathing exercises, such as those done in yoga, are excellent tools for maintaining or increasing lung capacity. In deep breathing, also known as diaphragmatic breathing, you breathe in through the nose to fill your lungs from top to bottom. Be sure to also breathe out as deeply as possible, so you get the maximum volume of air moving through the lungs. Adding resistance to the exhale by pursing the lips or tightening the throat is also beneficial.

It’s important to remember that age-related changes to lung capacity occur gradually. If you ever experience a sudden or dramatic change to breathing, which can signal illness or injury, see your doctor right away.

(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: My husband has had very bad breath for several months, and lately he says he has a metallic taste in his mouth. Can you tell us what might be the cause?

Dear Reader: Bad breath is a fairly common occurrence, as is a metallic taste in the mouth. The cause of these is usually something benign, such as a lapse in oral hygiene. However, each can be a sign of a more serious condition, so it’s worthwhile to figure out what’s going on.

Let’s start with bad breath, or halitosis. A frequent cause is the presence of bacteria that live on the surface of the tongue, below the gumline and in the throat. These tiny organisms, which feed on the food particles left behind when we eat, emit an array of stinky gasses as a byproduct of their digestion. Two compounds in particular contribute to foul-smelling breath. They are hydrogen sulfide, which smells like rotten eggs, and methyl mercaptan, which smells like putrid cabbage.

Some foods that we eat, such as onions and garlic, can also contribute to bad breath. Additional common causes for unpleasant breath include the poor dental hygiene that we mentioned earlier; an infection in the mouth, teeth or gums; the use of tobacco products; or interactions with certain medications or multivitamins. Saliva plays an important role in keeping the oral cavity clean, and a condition known as dry mouth, or xerostomia, can lead to bad breath. Chronic acid reflux, sometimes referred to as gastroesophageal reflux disease, or GERD, is also associated with unpleasant odors in the mouth.

When it comes to the reasons for a metallic taste in the mouth, there’s a bit of crossover with halitosis. Poor brushing habits, certain foods and an oral infection can play a role. So can pregnancy, cancer treatments like chemotherapy and radiation therapy, and environmental exposure. Some medications may cause a metallic taste, as can multivitamins containing zinc or copper. People who follow low-carb diets often report developing a persistent metallic taste, a side effect of their bodies being in ketosis.

However, the complaint is also associated with several more serious conditions. The perception of unusual flavors can occur in certain cancers when tumor growth affects the complex cellular pathways involved in taste and smell. They can also occur in diabetes, as a result of alterations to glucose metabolism. Kidney disease, liver disease and some metabolic disorders, which are marked by a buildup of waste products, can cause both bad breath and changes to taste. Taste abnormalities are also often seen in people with dementia, due to disease-related changes in the brain.

Since both the bad breath and the metallic taste are somewhat recent changes, we think it would be a good idea for your husband to see his dentist. A thorough checkup will reveal any tooth decay, gum disease or infection. If nothing turns up and you’re still worried, consider a visit to your primary care physician, who can help identify any underlying medical problems that require attention.

(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.)