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    Why Women's Libido Wanes

    Study Shows Cause Is Variations in Testosterone, Not Reduced Levels

    WebMD Health News

    Oct. 16, 2002 -- When sexual desire cools in middle-aged women, as it does for an estimated 40 million Americans, experts have often suspected a cold fact: The natural decline in the sex hormone testosterone that typically begins about five years before menopause.

    But a new study suggests that it's not necessarily reduced testosterone that cause women to lose that loving feeling, but fluctuations in levels.

    Researchers at the University of Pennsylvania followed 333 women between ages 35 and 47 for four years, measuring their hormone levels every six to nine months.

    They found that women who reported decreased libido typically had testosterone levels similar to those of women with sustained desire. However, women who showed the greatest variation in hormone levels were three times more likely to be sexually disinterested. The researchers presented their findings Tuesday at the annual meeting of the American Society for Reproductive Medicine.

    Although commonly considered a "male hormone," women also produce small amounts of testosterone in their ovaries and adrenal glands to help maintain muscle strength, as well as contribute to sex drive. Prior to the onset of menopause, levels naturally begin to wane -- along with sexual desire in an estimated 45% of those perimenopausal women. After natural or surgical menopause, testosterone production drops even more.

    Fluctuation can occur for several reasons, including the time of day.

    "We do know that testosterone levels tend to be higher in the morning and lower in the evening," notes Michael P. Born, MD, professor of gynecology at the Mayo Clinic in Jacksonville, Fla.

    Taking oral estrogen medications, like those used in hormone replacement therapy, may also have an impact. Hormone therapy can cause a decrease in the amount of testosterone, Born says.

    Testosterone may "drastically drop to levels that could be manifested into a decrease in desire," says sexual health expert Lana Holstein, MD, of the University of Arizona School of Medicine. She is also director of Women's Health at Canyon Ranch Health Resort and the author of the book How to Have Magnificent Sex: The Seven Dimensions of a Vital Sexual Connection.

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