The effects of both natural and synthetic hormones at extremely low doses

You’ve said that the doses at which hormones affect the body are extremely low. Give me an example to make me understand that.

F Vom Saal:  “The issue of the amount of hormone that actually causes effects is very difficult for scientists to talk to people about because we’re dealing with numbers that are outside of the frame of reference that anybody is going to be thinking about. We see changes, profound changes, in the course of development of essentially the whole body of experimental animals, and we’re working with mice and rats, and we see these changes at fifty femtograms of the hormone per milliliter of blood. That’s 0.05 trillionths of a gram of this hormone in a milliliter of blood.”

And what sort of effect does it have?

F Vom Saal:  “We see changes in the functioning of the prostate. We see dramatic change in the sprouting of glands within the fetal prostate. We see changes in testicular sperm production. We see changes in the structure of the endocrine control region in the brain, which is accompanied by changes in sex behavior, aggression, the way these animals behave towards infants, their whole social interaction, the way they age, the time that they enter puberty, the age at which they cease reproduction. It changes their entire life history, and these changes are capable of occurring at very low levels of hormones.
I remember when we first did this and I was a post doctoral fellow, and my advisor and I looked at the hormone levels and said, “My God, these levels are so staggeringly small and the consequences are so immense it’s amazing.” Even to biologists, it’s amazing.

But what you have is the entire field of toxicology thinking of a millionth of a gram of a hormone or a chemical as being this staggeringly tiny amount, and to most people if I said there’s only a millionth of a gram of it here you’d say, “How can it do anything?” A millionth of a gram of estradiol in blood is toxic. The natural hormone is actually operating at something like a hundred million times lower than that. So when you have a physiologist thinking of a millionth of a gram, you have that physiologist thinking this is a toxic high dose. When you are raised in the field of toxicology you are looking at that from the other perspective of “My gosh, that’s such a tiny dose, it couldn’t do anything.”

So now what we have are two different fields coming into this issue and looking at a dose as either staggeringly high or staggeringly low, and it’s not surprising that there is a clash occurring with regard to dose effects.”

Continue reading the interview conducted in February 1998 by Doug Hamilton, producer of FRONTLINE’s “Fooling With Nature.”, February 1998.