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Bis-phenol A, also known as BPA, is one of the world's most common industrial chemicals. It is used to make plastics that are clear and tough. It is also used to make epoxy resins, a kind of glue that appears in almost all food and beverage containers. BPA is used to make PVC pipe, dental glues, sports equipment, and the lenses used in eyeglasses. Worldwide, chemical plants make about 1.1 millions tons of BPA every year for use in making plastics.
In the United States, just about everyone has been exposed to enough BPA that it spills over into their urine. A study by the CDC found that 95% of adults in the 1990's, and 93% of children and adults in 2004, had consumed enough BPA that it was found in their urine. People who eat lots of fresh fruits and vegetables tend to have lower levels of BPA (probably because they aren't using as many cans and microwave containers that contain BPA) than people who eat mostly prepared foods.
What's the Problem with BPA?
Scientists conducting studies with lab rats noticed that BPA has some of the same effects in the human body as estrogen as early as the 1930's. The chemical was not widely used, however, until the late 1950's, and by that time, these studies had been forgotten. Only in 1997 did scientists establish that BPA acts as a xenoestrogen, a source of estrogen from outside the body. It has a molecular configuration that is very similar to 17-beta-estradiol, and it "locks on" to some of the same receptor sites on the surfaces of cells as estradiol.
It temporarily increases the production of testosterone, but a man's body converts the excess testosterone into estrogen in his fat cells. The greater a man's fat mass, the greater his production of estrogen, with its feminizing characteristics. Making matters worse, estrogen encourages the growth of fat, especially in the buttocks, which are 10 times more efficient at converting testosterone into estrogen than fat in other parts of a man's body. Still worse, the surge in estrogen increases appetite.
BPA Causes Us to Eat Too Much
BPA, like 17-beta-estradiol, suppresses circuits in the brain that regulate appetite. When BPA locks onto certain receptor sites in the brain, we want to eat, and eat, and eat. If we want to eat chips and crisps, which are sealed into plastic bags with BPA, and drink sugar-sweetened beverages, which are sealed into cans with BPA, and microwaveable meals, which are sealed with clear plastic made with BPA, the act of eating indirectly increases our appetite.
BPA is disruptive for adults seeking to maintain a healthy weight, but recent research from the University of Michigan suggests that it may be even more disruptive for infants who are exposed to the chemical before birth. The reason BPA is especially toxic to the fetus is not especially hard to understand.