Follicle-stimulating hormone, usually abbreviated as FSH, is a hormone produced by the anterior pituitary. FSH stimulates immature follicles in the ovary to mature and to release estrogen.

Normally the ovary also responds to FSH by releasing inhibin, another hormone, which then results in a decrease in FSH levels - creating a sort of feedback system to regulate the levels of each other and other hormones such as estrogen. At menopause when estrogen levels fall, the pituitary starts releasing even more FSH as if it is trying to get the estrogen levels back to where they once were. Consequently, post-menopausal women have high levels of FSH.

Osteoporosis is pretty common in post menopausal women, when the amount of bone mass being broken down (resorbed) is greater than the amount of new bone being formed. It has long been believed that estrogen has a major role in this process since estrogen levels decrease after menopause and many of the molecules involved in the resorption of bone are affected by estrogen.

However some recent research now shows that FSH also plays a role in this bone loss. A group led by Mone Zaidi - a researcher at the Mount Sinai School of Medicine in New York City - has recently published a paper demonstrating this.

Earlier experiments by other groups showed that mice without estrogen activity only show a mild or no bone loss.
Mone Zaidi’s group showed that ”FSH stimulates the formation and function” of cells that resorb bone in female mice, and that FSH is necessary for this bone loss. They also showed that in mice without FSH receptors (FSH will not function as usual with no FSH receptors present), bone loss decreased compared to ovariectomized (no ovaries, no estrogen) mice. In addition they showed that the decrease in bone loss was not due to the FSH causing an increase in bone formation

So what does this all mean? In a nutshell - most of the bone loss after menopause is likely not due to the decreased levels of estrogen, but rather due to the increased levels of FSH. In the future medications that inhibit the activity of FSH could be used to prevent osteoporosis. Much more research will be needed first of course before a drug like that would be ready for human use - but this is a very big step in osteoporosis research!

This work of Zaidi’s has been published in the April 21, 2006 issue of Cell (Volume 125, Issue 2, pp. 247-260, titled: FSH Directly Regulates Bone Mass).

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