Skeletal implications of reproductive aging.

The skeleton's density (mineral content and strength) is due to genetics (60%), nutrition (20%), and sex hormones (20%). The last factor increases bone density at puberty, mostly due to estrogen production. During reproductive aging as the ovaries lose most of their follicles, estrogen production declines. Bone collagen and mineral content decreases as the total cyclic estrogen production declines until the postmenopausal phase of life, at which point the 20% gained at puberty has been lost. This process starts before menses have changed, when fertility starts to be reduced. The most rapid loss of bone density occurs after actual menopause. Thereafter the rate of bone substance loss slows to the same rate as seen in aging men and is likely related to aging itself. In conclusion, decline in estrogen production is a major cause of bone mineral decrease.