Hello, dear readers, and welcome to our monthly letters column. We are deep into flu season. After a quick glance at the latest data -- up to 22 million infections, 10 million medical visits and at least 160,000 hospitalizations -- we are once again urging our readers to take all precautions, including getting this year’s flu shot. The flu is miserable, dangerous and unpredictable, and we think it makes sense to grab any advantage you can. And now, onward to your questions.

-- In a recent column, we mounted a spirited defense of oatmeal, which had been disparaged as nutritionally useless by a doctor who is popular on social media. We were happy to be able to say that, in addition to delivering important nutrients, oatmeal contains a type of soluble fiber that supports metabolism and contributes to the health and diversity of the gut microbiome. The topic led to this question from a reader: “In the column you mention cooked oats several times,” she wrote. “Are uncooked oats equally nutritious, or does cooking make some of the nutrients more readily accessible for the body to use?” Cooked and uncooked oats have the same basic nutritional profiles. However, cooked oats may be easier to digest, which would make the nutrients more available. When it comes to beta-glucan, the important soluble fiber we mentioned, research shows that both cooked and uncooked oats have equal amounts.

-- We recently wrote about bird flu, also known as H5N1. It can move from animals to humans and cause infections that range from mild to severe. We have heard from several readers asking about transmission. “Has there been any human-to-human transmission of bird flu?” a reader from California asked. Although there have been several cases of bird flu in people, at this time there are no known cases of human-to-human transmission of bird flu in the U.S.

-- A reader from Pennsylvania who dipped into our archives has a precaution to add to a column about how to stay safe while hiking in extreme heat. “Please remind hikers to let someone -- a friend, family member, neighbor -- know where they are going to be hiking, when they are leaving and when they expect to be back,” she wrote. “Although cell reception is often poor or nonexistent in many hiking locations, having a fully charged cellphone is also a good idea when starting out on a hike on a hot day.” Thank you for this important advice. We have also been hearing from people who hike in snow and cold, and will soon have a column about safeguarding your health in those circumstances.

Thank you to everyone who took the time to write. It is a pleasure to hear from so many of you. Please know that we read all of your letters and respond to as many as we can. Also, it is time for a reminder that we cannot offer a diagnosis, a second opinion, make referrals, look at your personal medical data or comment on specific treatment plans.

(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 to laugh when I saw there’s another new study about coffee. This one says it’s good for your gut microbiome. I’m 41 years old and a lifelong coffee drinker, and those studies come out like clockwork. Sometimes it’s good news, sometimes it’s bad. I’d like to know more about this one.

Dear Reader: There is no question that coffee is an extremely popular subject of study. Research into its possible health effects, both bad and good, dates back decades -- and small wonder. In the United States, coffee is by far our favorite beverage. We drink more of it than tea, soda and juice combined. Thanks to the caffeine it contains, coffee is a stimulant. That means habitual use can lead to a mild form of physiological dependence. Skip your daily brew and, as many regular coffee drinkers can attest, a nasty headache can be on the horizon.

That said, coffee is fascinating. A product of fermentation, it contains hundreds of chemical compounds, many of them bioactive. It also provides small amounts of magnesium, B vitamins and potassium, and it contains scores of phytochemicals with anti-inflammatory and antioxidant properties. Previous research has linked regular coffee drinking to improved blood sugar control, improved liver health, a lower risk of colon cancer and a reduced risk of developing diabetes, fatty liver disease and depression. With each advance in research tools and tech, investigators discover something new about coffee. And that’s where the study you are asking about comes in.

Because the gut microbiome plays such an important role in health and well-being, a team of researchers in Europe chose to explore how coffee may affect it. They analyzed health and medical data gathered from 75,000 people from 25 nations. The information included details about each person’s coffee consumption. The researchers also compared genetic and microbial profiles of stool samples collected from coffee drinkers and those who did not drink coffee.

The researchers found that people who regularly consume coffee have robust communities of a specific bacterium. Known as Lawsonibacter asaccharolyticus, this is a gut-friendly microbe that produces a compound called butyrate. For fellow science nerds, butyrate is a short-chain fatty acid. It helps moderate inflammation, bolsters the health of the gut-brain axis and is believed to contribute to the health of the cells that line the colon. People with a regular coffee habit had levels of Lawsonibacter asaccharolyticus that were eight times higher than nondrinkers. This held true no matter where in the world the study participants lived.

Researchers are now interested in learning if the known health benefits of coffee may be linked to high levels of Lawsonibacter asaccharolyticus. More study is needed to know if this is the case. The other interesting aspect of this study is the light it sheds on the growing awareness of the influence of diet on the gut. Not only do the foods we eat either nourish or harm the gut microbiome, but specific microbes appear to respond to specific foods. Now there’s (and here comes a dad joke) food for thought.

(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 just saw on the news that the smoke from wildfires is even worse for your health than we thought. Why is that? It seems like the smoke spreads for miles, so I’m worried. Is there anything we can do?

Dear Reader: Unfortunately, you are correct about all of this. Wildfires have not only become more frequent, they are burning hotter and longer. The National Interagency Fire Center reports that more than 61,000 wildfires burned close to 9 million acres across the United States last year. And while the fires themselves are local, the smoke they emit is not. As so many of us have experienced, wildfire smoke travels great distances. It can affect people living hundreds of miles, and sometimes even thousands of miles, away from the blaze.

The news reports you saw appear to be prompted by several new studies. One found wildfire smoke now accounts for one-fourth of the dangerous air pollution in the U.S. Other new research suggests that as fires burn, microbes in the fuel and soil are lofted into the air and carried far from their original locations. In the West, this includes a genus of fungi known as Coccidioides, which causes valley fever, a serious respiratory illness. Many wildfires now spread to urban areas. This adds plastics, polymers, chemicals and the host of other materials in our built environment to the toxic mix.

One of the things that makes wildfire smoke so dangerous is the high levels of fine particulates it contains. The most dangerous of these are known as PM2.5. The letters stand for the words “particulate matter,” and 2.5 refers to their microscopic size of less than 2.5 microns. When you breathe in air that contains wildfire smoke, these minute particulates enter the airways. They travel deep into the lungs, where they lodge in and inflame the delicate tissues. PM2.5 are so small, they can also pass into the blood stream and travel throughout the body.

All of this makes it crucial to take the health threats of wildfire smoke seriously. It is particularly true for people living with asthma, allergies and chronic obstructive pulmonary disease (COPD), and people with chronic heart disease. Exposure to wildfire smoke can cause throat irritation, watery or itchy eyes, sneezing, coughing, wheezing, a runny nose, congestion, rapid heartbeat, chest discomfort, shortness of breath and exhaustion.

Protect yourself by tracking air quality in your area. Whenever it drops to unhealthful levels, take steps to minimize exposure. If possible, stay indoors. Keep windows and doors tightly closed. If your home has central air conditioning or a HEPA filter, use it. But don’t run window AC units, as they draw unfiltered exterior air into the home. Protect indoor air quality. Don’t burn candles, use aerosol sprays or stir up indoor particulates by vacuuming or dusting. Avoid any unnecessary exertion.

Anyone who uses a rescue inhaler should have one ready. Check regularly to see if anyone is experiencing adverse symptoms, and be willing to seek medical help if needed. If you do have be outside, wear an N95 or better mask, even when you can’t smell or see the smoke.

(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.)