Dear Readers: When we first began writing this column, we wondered how we would know if we were reaching anyone. The answer came almost immediately, via your letters, all of which are read. It has been heartwarming to learn that we have helped many of you, delightful to discover how studious and curious you are about science and medicine, and humbling to have you engage us at such a personal level about your health issues and your lives.

We quickly learned that some of our columns, in which we answer a specific question or discuss a particular topic, give rise to a host of new questions. Many of these can and will be answered in future columns. Some of the letters we receive are, unfortunately, so personal and specific that we are unable to address them. But even in these letters we often find a more universal question that can be useful to discuss in the future.

So far, the columns about veganism, shingles, postpartum depression, vitamin B12 and toenail fungus have sparked the liveliest discussions. Regarding the column about the specific nutritional needs of vegans, we received appreciative notes from families who are considering the move to a vegan diet. We were also taken to task for not congratulating the potential vegans who wrote to us for advice regarding their new direction.

The truth is, we are deeply appreciative of how engaged you, the readers, are in living the healthiest lifestyle possible. We celebrate every query that reveals an interest in a better life. We're thrilled when we can help and do our best to offer the most useful, well-rounded explanations and information.

In the future, we will revisit the question of shingles as well as the vaccine, delve deeper into the importance of vitamin B12, and explore the causes and cures of various types of anemia. An excellent question we received asked for advice on how to get the most out of the relationship with one's family physician. In an upcoming column, we will discuss what we do to create the most useful relationships with our patients, and how we strive to serve them.

Finally, the other category of letter we get is from individuals sharing some interesting and surprising solutions to the problems many of us face. This one came from a 94-year-old gentleman who was diagnosed with sleep apnea, which occurs only when he sleeps on his back. How to assure you don't roll over onto your back once you're asleep? His family doctor had an ingenious solution:

"As suggested by my doctor, my wife sewed a pocket on the back of my pajamas to hold an everyday tennis ball. It was easily removable for washing. Since then, I have slept very comfortably, but only on one side or the other. And no longer do I snore."

So thank you again for making this column part of your lives and for taking the time to write to us. We, in turn, will make responding to your letters part of ours.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: A new study said that working out too much could ruin your sex life. I like to be in shape -- but not at that high a price. What's the deal?

Dear Reader: Exercise is unequivocally good for men's libido. Compared with sedentary individuals, men who exercise regularly have higher testosterone levels, greater libido and greater fertility. But extreme exercise is not without risks. Hormones are complex, and although the body is adept at regulating them through feedback mechanisms -- a finely tuned system known as the hormonal axis -- that feedback can be disrupted. In women, chronic endurance exercise training can lead to disruption of the hormonal axis, which can affect their menstrual cycle and fertility. It can similarly disrupt men's hormonal axis, leading to testosterone levels at the lower end of normal. The question is: What degree of exercise leads to this disruption, and does the disruption lead to decreased libido?

The study you mentioned, published earlier this year in Medicine and Science in Sports and Exercise, attempted to answer this question -- at least among men. Male subjects filled out online surveys about their level of exercise and their level of libido. Data were gathered from participants who were healthy, free of hormonal disorders, not taking prescription medications, older than 18 and involved in sporting activities. The researchers' primary focus was those men involved in organizations associated with endurance running, biking or triathlons.

Of the men who filled out online surveys, 1,077 men met the overall criteria, with respondents answering questions about the total number of hours exercised per week and the level of exercise intensity. The researchers also separated the men into two groups: low libido and normal-to-high libido. Notably, there were considerably fewer men in the low-libido group: only 60 compared to 1,017 in the normal-to-high libido group.

In men reporting normal-to-high libido, 33.1 percent exercised 4 to 6 hours per week; 35 percent exercised 7 to 10 hours per week; and 22.2 percent exercised more than 10 hours per week. Conversely, in the low-libido group, 10 percent exercised 4 to 6 hours per week; 23.3 percent exercised 7 to 10 hours per week; and 65 percent exercised more than 10 hours per week.

Researchers also assessed level of intensity and how many years the participant had been exercising at that intensity. In the low-libido group, there were three times as many intense/prolonged exercisers than there were moderate intensity/duration exercisers.

So, yes, this study shows that males who exercised at a high intensity for many years had a lower libido than those with a more moderate track record. But keep two things in mind. One, the low-libido group consisted of only 60 people, so the power of the data is not strong. Two, 22.2 percent of men in the normal-to-high libido group exercised more than 10 hours a week; 65 percent in the low-libido group exercised that much. Unless you exercise more than 10 hours per week, every week, I wouldn't be concerned.

That said, if you're finding that your libido is low and you're exercising more than 10 hours per week, you might want to reconsider your priorities.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: Is there anything I can do to reduce my risk of prostate cancer? No one in my family has had cancer, but I just turned 55 and want to do whatever I can to stay healthy.

Dear Reader: While there is no single approach to prevent prostate cancer, research has shown that certain lifestyle changes may reduce your risk of developing the disease. Considering that these behaviors also promote good health and well-being, you won't go wrong by adopting any or all of them.

Let's start with some facts about the disease.

Prostate cancer is the second-most common cancer in men, right behind skin cancer. According to the American Cancer Society, one in seven men will get a diagnosis of prostate cancer during his lifetime. However, that's not as dire as it sounds. Prostate cancers grow slowly and are slow to spread. As a result, survival rates of prostate cancer are high. The five-year survival rate is close to 100 percent. The 15-year survival rate is 95 percent.

The major risk factors for prostate cancer are age, race, family history, a diet high in red meat and animal fat, and tobacco use. While the first three can't be changed, they can alert you to be more vigilant.

About 70 percent of new cases of prostate cancer occur in men 65 and older. Men of African-American descent are at higher risk of developing the disease, and their cancers can be more aggressive. If you fall into those categories, and if cancer runs in your family, be sure to always include these facts in your medical history.

So how do you reduce your risk? Limit or skip red meat, dairy and animal fats. Opt for lean proteins like chicken, fish and turkey instead. Focus on healthy fats from plant-based sources like olive oil and nuts.

We're sure you've heard it before, but that's because it's true: leafy greens, whole grains and fresh fruits and vegetables provide a wide range of vitamins, minerals and fiber. Cooked tomatoes (which contain lycopene), cruciferous vegetables like broccoli and cauliflower, soy products and green tea are also recommended.

Studies show that being obese or overweight is linked to higher rates of many kinds of cancer, including prostate cancer. Regular physical activity, which not only burns calories and fat but also builds muscle mass, results in a lower -- and healthier -- body mass index.

Do you use tobacco products? As physicians, we must ask you to please stop. Tobacco plays a role in a daunting array of diseases and conditions, including prostate cancer. We know that quitting can be difficult and have given our own patients a hand in leaving tobacco behind. Don't be afraid to ask for help from your physician.

Cancers that are caught early are more easily treated. That makes screening important. Thanks to new understanding about slow-growing prostate cancers, many physicians will now recommend active surveillance in older men with slow-growing tumors.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)