Dear Doctors: I was recently sick with what I thought was the flu. I had a fever, sore throat and a terrible cough. I have asthma, so my husband insisted that I see our family doctor. She said that I did have the flu, but I also had acute bronchitis. Can you please explain what that is?

Dear Reader: Acute bronchitis is a respiratory tract infection that involves two of the major airways in the lungs. It is usually caused by a viral infection, and as happened with you, it can follow a case of the flu. Less often, a bacterial infection can be the cause. If left untreated, acute bronchitis can lead to more serious health problems, including pneumonia. People living with asthma and those who smoke have an increased risk of developing bronchitis during a respiratory illness.

To better understand the condition, we should begin with a bit of anatomy. When you breathe in, air enters through the nose or mouth and is directed into the trachea. Also referred to as the windpipe, this is the long, flexible tube that carries air toward the lungs. At its base, the trachea splits into two branches. These are the bronchi. (For fellow science nerds, each one is called a bronchus.) One of these branches leads to the left lung and the other to the right lung.

After the bronchi enter the lungs, they continue to divide into increasingly smaller and narrower branches, much like the canopy of a tree. At their smallest, now known as bronchioles, they connect to the more than 280 million tiny air sacs, or alveoli, located deep within each lung. These alveoli do the crucial work of delivering oxygen to the blood and receiving carbon dioxide, which is a waste product, to be exhaled.

When someone has bronchitis, it means that an infection of some kind has caused the inner lining of the bronchi to become inflamed. The immune system increases the production of mucus in the bronchi in an effort to trap and clear out the invading microbes, leading to the primary symptom of bronchitis. This is a deep, hacking cough, which typically brings up thick phlegm. It may range in color from clear to yellow to greenish.

People with bronchitis may feel short of breath and hear a wheezing sound as they breathe. Lingering irritation can cause continued coughing for several weeks after the initial infection has cleared. Because the increase in mucus production can decrease the amount of oxygen delivered to the blood by the alveoli, people with bronchitis often feel fatigue and tire easily during exertion. Additional symptoms of this illness are similar to those of other upper respiratory tract infections. They include fever, headache, body aches, chills and a sore throat.

Treatment focuses on management of symptoms. This includes medications to ease cough and physical discomfort and to lower fever. Expectorants, which thin out mucus and make it easier to expel, may be prescribed. It is important to stay hydrated, get plenty of rest and not overdo it when you return to your daily routine.

(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 always thought that your body ages gradually as you get older, kind of like your car does. But now I’ve been hearing that we actually go through a couple of spurts where we age really quickly. Can you please explain where this idea comes from?

Dear Reader: You’re referring to a study that made quite a splash when it was published last summer. Researchers at Stanford Medicine upended the idea that we age at a steady and measured pace throughout the course of our lives. Instead, the results of their research suggest that our bodies undergo two periods in which significant changes that take place at the molecular level add up to a sudden acceleration in aging. The first occurs at age 44 and the second at age 60. Not surprisingly, the idea that aging isn’t directly tied to chronology is still making headlines months later.

Working with scientists in Singapore, the researchers wanted to understand why the risk of certain diseases and health conditions appeared to spike at specific time points. In middle age, people often begin to get muscle injuries and see a marked increase in body fat percentage. In older age, they begin to lose muscle mass and develop an increased risk of cardiovascular and neurodegenerative disease, kidney disease and Type 2 diabetes.

To learn the reasons for these patterns, the research team recruited 108 adults ranging in age from 25 to 75 to take part in a multiyear study. The participants were asked to donate blood, stool, skin, nasal and other biological samples every few months. The researchers then analyzed age-related changes taking place in more than 135,000 different proteins, microbes in the gut, mRNA and other molecules. They found that at about age 44, and again around age 60, these molecules undergo rapid changes that correlate to the specific health risks associated with those ages.

For example, when you reach your mid-40s, a marked shift in your ability to metabolize alcohol occurs. That’s why the night out that barely fazed you in your 20s leaves you in rough shape in middle age. Other shifts include the ability to metabolize caffeine and changes to lipid metabolism and skin and muscle tone. In your 60s, caffeine metabolism takes another hit. So do the immune system and, again, muscle and skin. Interestingly, the data also suggest that some of the midlife changes that have been attributed to hormonal shifts in women during perimenopause are actually taking place at a molecular level and in both sexes.

So, how does this translate to daily life? At the most basic level, it underlines the importance of sticking to a healthful diet throughout your life. As you reach middle age, adjust your diet to anticipate fat gain and implement exercise routines to prevent muscle injuries. Caffeine drinkers should make appropriate changes. Ditto for alcohol use. Older adults can prepare for an accelerated rate of muscle loss, known as sarcopenia, by engaging in age-appropriate weight-training programs. The study also emphasizes the importance of regular health screenings, particularly at these pivotal times of life.

(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'm pretty good about eating a healthy diet. The exception is each month during my period, when all I seem to want is potato chips and ice cream. Is there something going on with my body, or is this just a good excuse for a few cheat days each month?

Dear Reader: Eating a healthful diet means putting a daily limit on the sweet treats and salty carbs that can wreak havoc on weight management, blood pressure and blood sugar. That kind of sustained discipline makes the occasional cheat day a welcome break. But when it comes to the intense food cravings that can occur during the menstrual cycle, years of research suggest that the many changes taking place in the body during that time are a significant factor. These include rising and falling levels of estrogen, progesterone, cortisol, serotonin and insulin. Levels of ghrelin and leptin, the so-called hunger hormones, also seesaw during the menstrual cycle. Ghrelin boosts feelings of hunger, whereas leptin promotes satiety.

Now, a small study from researchers in Germany, which was published last year in the journal Nature Metabolism, suggests that brain chemistry plays a significant role in period cravings. Specifically, the cycle of hormonal shifts that take place during a woman’s menstrual cycle cause the brain to become more sensitive to changes in insulin levels. The hormone insulin, which is produced by the pancreas, regulates blood sugar. It is also able to cross the blood-brain barrier. The body’s response to insulin has an effect on hunger and cravings.

The researchers conducted two experiments. In the first, they used a device known as a glucose clamp to measure changes to insulin sensitivity in the brains of 11 young women as they went through the phases of a menstrual cycle. They found that during the follicular phase, which is when the egg is being prepared to leave the ovary, the brain becomes more sensitive to insulin. Insulin sensitivity is associated with good blood sugar control and a stable appetite. But during the luteal phase, which is when the egg travels to the uterus and waits to be fertilized, insulin sensitivity in the brain measurably decreased. That suggested that this phase of menstruation, which is when food cravings typically occur, is marked by insulin resistance. This is a metabolic state that prevents the cells from absorbing glucose from the bloodstream, which in turn can cause an increase in hunger.

In the second experiment, conducted with a different group of 15 young women, the researchers again measured changes to insulin sensitivity throughout the phases of a menstrual cycle. The women underwent MRIs, which verified the original findings.

The idea that insulin resistance in the brain can have an effect on appetite is intriguing. It not only offers an explanation for the food cravings that many women struggle with during their periods, but it also points to new avenues of research in obesity and diabetes. However, as is true of all small studies, this is just a beginning. More research is needed to confirm these findings and to further explore their effects on the body.

(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.)