BPA: What is Bisphenol A doing in baby bottles and why is it a problem?

You may have read news reports about the potential dangers of certain plastic baby bottles.  The concern stems from Bisphenol A, which is present in polycarbonate plastic.  Many baby bottles are made from polycarbonate plastic, as are countless other consumer items.  Polycarbonate plastic is widely used plastic.  It is clear, lightweight, heat resistant, and shatter resistant.  It is used in a wide variety of applications, many of them involving direct contact with foods and beverages, including baby bottles, reusable sports water bottles, food storage containers, and tableware.  

Plastics are like very long trains made up of identical railroad cars.  The technical explanation is that most plastics are polymers, or are long molecules (the very long train) made up of many repetitions of a basic molecule called the monomer (the railroad car).  Bisphenol A is the basic monomer of polycarbonate plastic.  Bisphenol A (BPA) is a synthetic chemical compound used in a wide range of consumer products.  It has found its way into the bodies of most of us.  A study in the US found that 95% of people tested had been exposed to BPA.

Bottle FeedingUnder certain conditions, BPA leaches out of the polycarbonate and into the food or drink.  What are those conditions?  Well, it is uncertain, but it appears that leaching occurs with everyday use, and is much higher when the bottles are scratched or worn.  It also appears that leaching is much worse when the bottles are heated.

Exposure to BPA may cause health effects.  The safety of BPA is being hotly debated right now.  The U.S. Food and Drug Administration and the plastic industry maintain the BPA is safe at the levels to which most consumers are exposed.

However, some research scientists have been increasingly warning consumers about potential dangers.  BPA has been shown to be an endocrine disruptor and to simulate the action of the human hormone estrogen.  Early life exposure may cause stimulate certain cancers and may cause genetic damage.

The National Toxicology Program (NTP) Center for the Evaluation of Risks to Human Reproduction convened an expert panel to evaluate BPA.  The Panel’s final report is scheduled to be published in Fall 2007, but the draft meeting summary identifies the following conclusions:

For pregnant women & fetuses:

  • Some concern the exposure to BPA in utero causes neural and behavioral effects

  • Minimal concern that exposure to BPA in utero causes effects on the prostrate and accelerations in puberty

  • Negligible concern that exposure to BPA in utero produces birth defects and malformations

For infants & children:

  • Some concern that exposure to BPA causes neural and behavioral effects

  • Minimal concern that exposure to BPA potentially causes accelerations in puberty

For adults:

  • Negligible concern for adverse reproductive effects following exposures in general population

  • Minimal concern for highly exposed subgroups (e.g., occupational exposures)

Concern is rated as follows:  negligible, minimal, some, concern and severe.

Part of the problem is that there have been no human studies of BPA exposure.  More than 150 studies have found health effects in animals exposed to low doses.  However, scientists have reached different conclusions about whether BPA is safe in part because of metabolic differences between mice and humans and uncertainty in the amounts to which people are actually exposed.  Japan and the European Union’s Food Safety Authority recently reaffirmed BPA’s safety, criticizing the methodology of rodent/BPA studies as unreliable.  That’s really the root of the difference – these scientists haven’t agreed on how to translate the animal studies into human effects.

The Panel’s conclusions have been criticized by other leading experts.  In a consensus statement published in Reproductive Toxicology, a group of 38 scientists, including 4 from federal health agencies, concluded that people are exposed to levels of BPA exceeding those levels that harm lab animals, and that infants and fetuses are the most vulnerable.  This group of scientists reached these conclusions after reviewing about 700 studies.  Jerrold Heindel, a scientist with the National Institute of Environmental Health Sciences who organized a meeting last fall to begin drafting the statement, said even though there have been no human studies of BPA, there is now so much animal data that the 38 experts believe that human damage is likely.  “We know what doses the animals were given, and when we look at humans, we see blood levels within that range or actually higher, which is a cause of concern and should stimulate more human research,” he said.

In the statement, the 38 scientists say they are confident that BPA, which mimics the female hormone estrogen, alters cells to switch genes on and off, programming a fetus or child for reproductive disorders later in life, and that the levels that harm lab animals “are well within the range of … BPA levels observed in human fetal blood.”

They concluded that “early life exposure … may result in persistent adverse effects in humans.”

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