DEAR DOCTOR K:

Is the chemical BPA just another health scare? Or is it really something I should be worried about?

DEAR READER:

BPA stands for bisphenol A. It is used to make a plastic known as polycarbonate.

Polycarbonate is sturdy and resists shattering, so it's a great material for water and baby bottles. BPA is also used to line the inside of cans so the metal of the can doesn't directly touch the food or beverage. It's used in some dental sealants and as an ingredient in the paper on which many receipts are printed. So there's no question that we're exposed to BPA.

There's also no question that BPA can get inside us. The vast majority of Americans have measurable amounts of it in their bodies.

Adults are mainly exposed to BPA from canned food, because BPA escapes out of the cans' lining. Infants can be exposed from the linings of infant formula cans and from polycarbonate baby bottles. (But note that polycarbonate baby bottles are rarely sold in the United States and are banned in the European Union and Canada.)

BPA has effects similar to certain hormones in animals. The hard, and controversial, question is whether any of this exposure to BPA causes harm. Expert panels organized by the National Institutes of Health have concluded that there is reason to be concerned, although there is no proof of harm. The U.S. National Toxicology Program expressed concern about the possibility of brain and behavioral effects on fetuses and young children, at levels of exposure in the U.S. population.

Most of the concerns involve possible adverse effects on fertility, obesity and behavioral problems in young children. Some studies in animals raise questions about whether BPA can damage the breasts, thyroid and prostate glands.

Studies in mice and in monkeys have found adverse effects from BPA in concentrations that humans are exposed to. Since mice and monkeys are mammals like us, and share many genes with us, that is a reason for concern.

I have mixed feelings about all the focus on BPA. On one hand, no adverse effects in humans have been proven. On the other hand, it probably wouldn't hurt to be cautious about BPA exposure and to limit it where we can.

The first thing I would suggest is to eat less canned food. Replace it with more fresh fruits and vegetables -- and that's always a good idea.

If you continue to use containers that are made of BPA, don't put them in the microwave. Also, don't put hot foods or liquids in them: The heat can leach BPA from the wall of the container. Containers made of porcelain, glass, stainless steel and other types of plastic are safer for hot foods. For water bottles, consider switching from a BPA-containing bottle to one made of stainless steel. Unlike aluminum water bottles, the stainless steel ones tend to be unlined.

I would avoid altogether using BPA containers to contain liquids for young children.

Products that contain BPA have the number 7 on the bottom or recycling label, so you can use this as a way to identify and avoid buying them.

(Dr. Komaroff is a physician and professor at Harvard Medical School. Go to his website to send questions and get additional information: www.AskDoctorK.com.)

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