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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.)

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