Dear Doctor: I read that yoga mats can reduce fertility. If so, what's in them? Whatever it is can't be unique to just yoga mats.

Dear Reader: As happens with many health-related topics, that yoga mat story hit the news cycle thanks to the published findings of a scientific study. In this case, researchers were looking for a correlation between certain widely used flame retardants and the fertility of 211 women in an in vitro fertilization (IVF) treatment program.

Previous studies have indicated a link between infertility in animals and the presence in their bodies of organophosphate flame retardants, commonly referred to as PFRs. But as the researchers note, theirs is the first study to examine the effect of organophosphate flame retardants in human fertility.

Flame retardants are routinely incorporated into the manufacture of scores of items we all have in our homes. They can be found in couches, futons, upholstered chairs, carpets and carpet padding, TV sets and remotes, cellphones and children's products, including clothing, car seats and crib mattresses, to name just a few. They're present in many building products, plastics and some nail polishes.

These chemicals are so widespread that most of us living in the United States have measurable quantities of them in our bodies. Earlier flame retardants, polybrominated diphenyl ethers (PBDEs), were phased out of production in the mid-2000s due to health concerns. However, the PFRs that replaced them have drawn similar scrutiny.

In this new study, researchers chose to study healthy women undergoing IVF in order to account for as many variables as possible. Unlike in natural conception, when ovulation and fertilization are hard to pinpoint, each milestone of the pregnancy is monitored and recorded in IVF.

Participants also shared information like age, weight, race and ethnicity, their smoking history, their levels of education and whether they had ever previously been pregnant. Each participant's body mass index was calculated, and the levels of hormones crucial to successful pregnancy, such as FSH, were measured during the IVF process.

Researchers found a 10 percent decrease in the rate of fertilization among women with the higher levels of PFRs in their bodies. These same women had a rate of embryo implantation that was one-third lower than those with lower levels of the chemicals in their blood. The rate of live births was 38 percent lower.

The numbers are arresting, but as when any new information comes to light, we need more research to understand the whole story. The sample size of 211 women is small. The fact that the women are enrolled in an IVF program means they are already facing fertility problems. Also, the sperm involved in each attempt at pregnancy is not being evaluated.

However, decades of study have shown that the chemicals present in flame retardants do adversely affect various hormones. It's quite likely that, with the results of this most recent PFR study, the research will expand and move forward.

So what about the yoga mats that made it into so many headlines? It turns out that the study cited gym mats, those thick pads from PE class, as a source of PFRs. Most yoga mats are made of PVC and don't contain flame retardants.

(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: Are there any benefits to testosterone therapy for older men who have osteoporosis of the spine and hip? I understand that it comes with an increased chance of prostate cancer.

Dear Reader: These are smart questions to ask. Too many people think that men don't develop osteoporosis, but in fact, low testosterone is a prime risk factor for osteoporosis in men -- and not just in older men. Low bone density has clearly been shown in younger men whose testes produce very low levels of testosterone. For them, testosterone therapy has been shown to increase bone density after one year. For older men, the answers are more complex.

A 1996 study assessed the impact of testosterone therapy in 36 men with a median age of 58 who had testosterone deficiency verified by three different tests at different times. The men were given testosterone injections regularly for up to 18 months. At the end of the study, the testosterone had increased bone density in the spine by 5 percent while also increasing lean muscle mass and decreasing body fat.

A 2017 study looked at the impact in 211 men over the age of 65 (average age of 72) who had two morning testosterone readings below normal (lower than 275 nanograms per deciliter). The men were given the testosterone treatment AndroGel, of which they applied 5 grams daily to the skin for one year; a control group received a placebo gel. Both groups were given additional calcium and vitamin D. The testosterone group showed a 7.5 percent increase in bone density of the spine, while the placebo group showed an increase of only 0.8 percent. Hip bone density increased by 3.3 percent in the testosterone group, and by 2.1 percent in the placebo group.

A 2004 study also looked at men with low testosterone (below 350 ng/dL), with 24 men receiving an injection of 200 milligrams of testosterone every two weeks for three years, and 24 receiving a placebo injection every two weeks. At the end of the study, the testosterone group showed an improvement in spinal bone density by more than 9 percent; the placebo group showed no change. Again, there was only a slight improvement in hip bone density in the testosterone group.

Testosterone therapy clearly benefits men with low testosterone levels, so the natural question is: What about for men with normal levels? Unfortunately, there is no good data to support testosterone use in men with a normal level -- especially considering that testosterone increases both the size of the prostate gland and blood PSA levels. That is, there is a theoretical increased risk of prostate cancer with the use of testosterone. In men with low levels, using testosterone to bring those levels to normal may pose only a slight risk, but still, they should be monitored with PSA tests and prostate exams when on such therapy.

What appears to be more concerning is a slight increase in strokes and heart attacks in men using testosterone therapy. This risk appears to be correlated more strongly with injectable testosterone. And again, for men with lower levels, testosterone therapy may not show this risk.

In short, if your testosterone level is low and if you have a low risk for prostate cancer, you should consider testosterone therapy. Not only will it help build muscle mass, decrease fat, enhance libido and increase energy, it will also help increase your bone density.

(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.)

Hello, dear readers! We're back with our monthly column to continue our conversation regarding your questions, concerns and thoughts about previous topics.

-- We'd like to begin with those of you who have written to us about specific medical issues that you or your loved ones are facing. As we've mentioned before, we can't give medical advice or suggest a diagnosis in this column. However, from the content of these letters, it's clear that you have been in contact with medical professionals.

If the medical information you have received is unclear, we urge you to follow up with your providers. Make a list of your questions. (And, as a reader has suggested, it's a great idea to make two lists and give one to the doctor.) Rank the questions in descending order of importance and then go over each issue until you receive an answer that you understand.

If you're still not getting the information you need in the form that you need it, we urge you to seek a second opinion. It can be from an entirely new doctor, or it can be from a different person in your own physician's office. It's quite possible that a nurse, nurse practitioner or physician's assistant in your health care provider's office or medical group may have a different approach to the issue that works better for you.

The final piece is to be sure to write everything down. It not only gives you a record of what was said that you can refer to in the future, but the simple act of writing something down also helps you to realize whether or not you are actually clear about what is being said.

-- We've had a number of readers ask about our answer to a woman who was experiencing urine leakage due to stress incontinence. When we stated that there are no approved medications for this problem, we meant stress incontinence only. As many of you pointed out in your emails and letters, urge incontinence, also known as overactive bladder, can be treated with an array of FDA-approved medications.

-- As scientists, we admire precision. In that spirit, we'd like to acknowledge a lapse that someone pointed out in our column about Candida auris, the so-called superbug fungus that is wreaking havoc in some hospitals. At one point, we referred to this yeast as an "organism." It is, as are all yeasts, a microorganism.

-- We've been receiving quite a few letters regarding the column about sundowning, a late-day confusion that's common among individuals with Alzheimer's disease or other types of dementia. Many of you described experiences with loved ones where symptoms similar to sundowning were caused by medication imbalances or the lingering effects of anesthesia. This is an important topic that we will take up in an upcoming column.

As ever, we'd like to thank you for your interest in, contributions to and suggestions for our columns. Every one of your letters and emails are read, and we are grateful for the time you take to write and send them.

(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.)