(Reuters) - Despite concerns that removing both of a woman's ovaries would raise her chances of dying from diseases associated with aging, a large new study suggests the procedure may be safe.

Looking at data on more than 130,000 California teachers, researchers found that women who were 45 years old or older when they had both ovaries removed had a slightly lower chance of dying over the length of the study than peers who didn't have the procedure.

For women under 45 at the time of surgery, there was no increased risk of death over time, the authors note in the journal Fertility and Sterility.

Katherine Henderson, the study's lead author and an assistant research professor at the Beckman Research Institute of the City of Hope National Medical Center in California, told Reuters Health the study aimed to address a concern raised by a few past studies suggesting bilateral oophorectomies, the surgery to remove both ovaries, were linked with an increased risk of death.

Often women who are having their uterus removed during a hysterectomy are given the option to have their ovaries removed at the same time.

Taking out both ovaries is thought to reduce a woman's chance of developing ovarian cancer, which is hard to test for and catch in its early stages. Removing a woman's ovaries, which generate estrogen, thrusts her into menopause almost immediately with an unknown impact on long-term health, however.

In some groups of women, such as those with a family history of breast or ovarian cancer, the benefit of early menopause is clear, said Henderson in an email.

However in most women it's just not clear whether the downside associated with early menopause due to bilateral oophorectomy outweighs the benefits.

In 2007, about 20,000 U.S. women were diagnosed with ovarian cancer, and almost 15,000 died from it, according to the Centers for Disease Control and Prevention.

According to Henderson's study, about 600,000 women had hysterectomies every year between 2000 and 2004. More than half had their ovaries removed, too.

Over the past decade, a number of studies have produced conflicting answers to the question of whether ovary removal abruptly raises risks that tend to go up after natural menopause too, including death from heart disease, cancer and other causes.

Dr. William Parker of the John Wayne Cancer Institute at Saint John's Health Center in Santa Monica, California, who has published research linking ovary removal and increased risk of death said he notices younger doctors are more willing to accept that there might be a higher risk associated with the procedure than older doctors.

It's the gynecologist who sees the patient die of ovarian cancer, said Parker.

We're kind of operating with blinders on. We're very focused on this one condition.

You can't make a definitive conclusion, because the literature is so mixed, said Dr. Vanessa Jacoby, an assistant professor of obstetrics and gynecology and reproductive science at the University of California, San Francisco.

Jacoby told Reuters Health that studying an association between the removal of ovaries and death from heart disease or cancer is hard for several reasons. But one of the main reasons is that so much time has passed between the surgery and death.

Women typically have an oophorectomy with their hysterectomy in their forties. Heart attacks don't happen until much later, and so much time has passed. That is a very hard thing to study, said Jacoby.

Another challenge is that no two studies are alike, Parker added.

I don't think you can start adding all the studies together that (are) out there, because they're all so different, said Parker.

However, at the end of the day Parker said the decision needs to be made between the patient and her doctor.

In the end it becomes a very personal decision, as it should be, Parker said.

As always have a frank and candid conversation with your doctor about your therapeutic choices, said Henderson in an email.

If you face the decision as to whether to undergo a bilateral oophorectomy, you must carefully weigh the risks and benefits to you as an individual.

SOURCE: bit.ly/thqDUT

Fertility and Sterility, published online November 14, 2011.

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