Dear Doctor: I take a short nap at my desk a couple of times a week (I use earplugs and a mask), which my podmates love to tease me about. I just read that napping is good for your heart, but they say if you take a nap during the day, you won’t sleep as well at night. Who’s right?

Dear Reader: While it’s certainly possible that for some people, a midday nap may interfere with the quality of nighttime sleep, it’s not a given. In fact, a robust body of research has found numerous benefits of napping, both to physical and mental health. Napping has been shown to improve mood, increase alertness, improve performance and stave off late-afternoon fatigue. In many cultures, such as with the Spanish “siesta,” the Italian “riposo” and the Japanese “inemuri,” it’s an integral part of daily life. Here in the United States, the benefits of napping have led a growing number of employers to encourage their workers to take advantage of a lunchtime recharge. Some of the larger tech companies have even installed specially designed recliners, called nap pods, which weave the idea of napping into their corporate culture.

Most recently, a study published in the journal Heart has linked the practice of occasional napping to a decreased risk of heart disease and stroke. Researchers in Switzerland analyzed the nighttime sleep, daytime napping and general lifestyle habits of 3,462 adults between the ages of 35 and 75. About 20% of the study participants reported napping once or twice a week. At the end of eight years, the data suggested that those individuals had a lower risk of heart problems than the non-nappers. Interestingly, the same health benefits didn’t extend to the most frequent nappers in the study, who researchers said tended to be older men who smoked and were overweight.

The exact reason for the better health outcomes of the occasional nappers aren’t known. But inadequate sleep has been linked to a number of health problems, including high blood pressure, depression and heart disease, and the researchers suggested it’s possible that occasional napping helps to make up for sleep deficit.

That said, there’s an important distinction between a 10-to-20-minute nap in the middle of the day and dropping into deeper sleep for an hour or longer, particularly in the later afternoon. In those cases, not only do you run the risk of waking up thickheaded and groggy, which can take hours to shake off, it’s possible for a late-day dive into sleep to interfere with nighttime sleep. The goal of a nap is to wake up feeling refreshed. To achieve that, you want to limit your nap to less than 20 minutes. That lets you get the rejuvenating benefits of the early stages of non-REM sleep. If you stay asleep much longer, you run the risk of diving into the deeper stages of the 90-minute sleep cycle. Waking up from deeper sleep often leaves you feeling dazed and disoriented, and it can take hours to fully recover.

(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: Everybody is talking about the coronavirus right now, but I still don’t really know what a virus is. How do they work? Why don’t antibiotics kill them?

Dear Reader: You’re far from alone in your struggle to understand viruses. They are simultaneously simple and quite complex, and so small that it wasn’t until the invention of the electron microscope almost 90 years ago that we were even able to see them.

A virus is neither plant nor animal; it isn’t a bacterium, fungus or one-celled organism; and it can’t live or reproduce outside of a living host cell. Considering all that, it’s not surprising that the scientific community continues to debate whether or not viruses are even alive. In fact, it’s almost easier to talk about what a virus isn’t than to explain what it is. But we’ll do our best.

A single virus particle is known as a virion. It’s a packet of genetic material -- either DNA or RNA -- wrapped in a layer of proteins, known as a capsid. In many kinds of viruses, the protein shell is topped by a layer of lipids, a type of organic compound that’s roughly comparable to fat and is not soluble in water. Taken together, the protein and lipid structure is known as an envelope.

Viruses are mind-bendingly small. They range from about 20 nanometers to upward of 300 nanometers in size, with many tending toward the lower end of the scale. As a point of reference, there are 25.4 million nanometers in one inch. Viruses come in a wide range of shapes, including circular, cylindrical and stringlike. Some, like the coronavirus, are studded with spikes. These act as docking devices to attach to host cells and then use their unique chemical composition to penetrate the cell membranes.

The sole purpose of a virus is to infect another organism -- either an animal, plant or bacterium -- make billions of copies of itself and then move on to infect a new host. Small wonder the name for these infectious agents derives from a Latin word that roughly translates to “poisonous slime.”

To achieve its aim, the virion injects its genetic material into the host cell and hijacks that cell’s internal machinery. Instead of doing its designated job, the cell now goes to work replicating the virus. Each virion is so ruthlessly efficient, it can force a cell to make a million copies. The infected cells send out a chemical distress signal in the form of proteins known as cytokines. They set off the inflammatory reaction that causes our immune systems to attack, which results in the symptoms we feel when we’re sick, such as fever, congestion, coughing and sneezing, headache, body aches and gastric distress.

You are correct that antibiotics have no effect on viral illnesses. Antibiotics work by breaching a bacterium’s cell walls, which viruses don’t have, or disrupting its reproduction, which viruses do differently. Due to antibiotic resistance, which is now a serious problem, it’s important not to use these drugs to fight a viral infection. Instead, for viruses such as the flu, your doctor will prescribe an antiviral, which works by interfering when the virus tries to force the cell to make copies of it.

(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’m stalled on my resolution to quit eating sugar. Why is it so hard? I just can’t seem to stop saying yes to sweets, especially my favorites -- cookies and candy bars. Do you have any suggestions?

Dear Reader: First of all, please don’t feel bad. In your quest to control your sugar intake, you’re battling two powerful forces -- biology and modern food science.

Sugars provide the body with an efficient source of energy, and the pursuit of them is hardwired into our brains. This, along with the fact that sugar wakes up the reward centers of the brain, has been weaponized by food scientists. The result is a vast array of sweet treats, many of them amped up with fats and salt, and each carefully designed to be irresistible. Adding to these challenges is the fact that quitting sugar cold turkey can leave you with genuine symptoms of withdrawal, including headache, fatigue, irritability and low mood. But don’t despair. Armed with a bit of self-knowledge and a few deliberate strategies -- and, yes, some willpower and discipline -- you can successfully get your sweet tooth under control.

Start by becoming aware of how much sugar you eat, and when. Do you add it to your morning coffee or tea? Is it part of your breakfast? Do you drink sugared beverages? All of these, along with any candy, baked goods, ice cream or other sweet snacks that you grab throughout the day, contribute to the estimated 17 teaspoons of sugar that we Americans ingest daily. That’s double the recommended limit of 9 teaspoons per day for men and triple the 6 teaspoons for women, and it adds up to almost 57(!) pounds of sugar per person per year. Since 75% of all processed foods -- even those that come across as savory -- contain added sugars, you’ll need to check food labels for an accurate picture of your intake.

Once you’ve identified the sources of sugar in your diet, you can begin the process of weaning yourself off of it. If you’re stirring it in to coffee, cut back a little each day until it’s gone. If you’re a soda drinker, switch to one of the many varieties of sparkling water that have become available. It is helpful to understand that sugar makes blood glucose levels spike, which triggers the pancreas to release insulin. That’s the hormone that allows cells to absorb and use glucose for energy. A healthy blood sugar balance depends on limiting surges of insulin, so think in terms of meals and snacks full of protein, fiber and healthy fats. They will fill you up and lessen your cravings without making your blood sugar levels go crazy.

Artificial sweeteners may be tempting, but studies have linked them to a boomerang effect of craving more sugar, as well as to adverse effects on the gut microbiome. Plus, after just a few days of sugar abstinence, you’ll find that your taste buds are waking up to the natural sugars in foods, which will become satisfying. There’s no question that quitting sugar can be a challenge, so be kind to yourself and take things gradually.

(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.)