Tuesday, September 25, 2007

Environmental exposures

Several days ago I posted a question, asking how much risk is too much risk? I wanted to highlight the fact that homebirth advocates often don't know that the real risks of practices they favor (like homebirth) are substantially higher, even orders of magnitude higher, than the risks of practices that they oppose as "too risky". Partly this reflects a lack of knowledge about the real risks, but it also reflects the widespread and erroneous notion that most health problems are caused by environmental exposures.

Homebirth advocates, like most advocates of "alternative" health are obsessed with the fear of environmental exposure. They are sure that death lurks in artifical coloring and preservatives, that what you eat determines your health, and that you can control your health by what you eat. They are also obsessed about exposures to medications, believing that they can and do cause widespread harm to babies. Once again, when it comes to assessing relative risk, they are way off the mark.

Sandy Szwarc, at Junkfood Science has written an oustanding post on this topic, The greatest myths of birth defects — Should unborn babies fear the environment? She writes about Dr. Jon Aase, M.D., of the Division of Clinical Genetics/Dysmorphology and Metabolism at the University of New Mexico Children’s Hospital, who, at a recent conference, spoke about the top myths believed about birth defects.
Myth #1: Most birth defects are caused by environmental agents.

There are still unknowns about birth defects but what is known is often strikingly different from popular beliefs. The most believed fallacy about birth defects is that most are caused by environmental exposures, such as toxic chemicals, pollutants, radiation and other bad things. Heightening these scares is also popular among some environmental groups.

But amazingly, this is a myth. About 3% of babies are born with some type of congenital abnormality and most of those are single body system defects (club feet, heart defect) due to minor genetic factors and chromosomal aberrations. A very small percentage of birth anomalies — 1 in 500 births — are true “dysmorph” syndromes, or birth defects, which affect multiple systems of the body. And a tiny fraction of these (about 10%) are caused by environmental factors. But when dysmorphologists use the term “environmental” they are referring to any exposure in the environment of the unborn fetus...

Myth #2: Anything that causes birth defects in animals will cause birth defects in people.

These facts even astonished this audience of scientists. He reported that no human birth defect — either risk or type — has ever been predicted by animal studies. People are not rats or animals. In vitro studies have also failed to predict birth defects.

Myth #3: Any exposure to a known teratogen will cause a birth defect.

This is false. The only known thing to cause birth defects with any level of exposure — even a single dose — is thalidomide, which results in birth defects in 41% of cases...

Myth #4: A teratogen will always cause a birth defect.

The fact is, he said, no agent is always teratogenic. Radiation, for example, can be teratogenic in extremely high doses such as therapeutic levels used to treat cancers. But diagnostic levels as in chest X-rays, dental X-rays and mammograms and low environmental levels have never been shown to cause birth defects...
There are four additional myths. I highly recommend the entire article. It demonstrates that the popular claims about environmental exposures are utterly wrong.

What is particularly interesting to me when considering the subject of childbirth and risk is that there are many different types of risks, but homebirth advocates are only concerned with environmental exposures. So, for example, they are unreasonably obsessed with the purported "risks" of epidurals, yet completely unperturbed about the risk of preventable death at homebirth which is one thousand times higher. The are unreasonably obsessed about refined sugar and processed foods, but have no problem with the real risks of breech vaginal delivery. As I said before, this is partly the result of the fact that they actually don't know what the risks really are. However, it is also due to an unexamined and incorrect belief that environmental exposures represent the most serious health risks.

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