A recent study touting a list of unexpected health benefits for the birth-control pill was wrong and should be discounted, say scientists with the landmark Women's Health Initiative...

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A recent study touting a list of unexpected health benefits for the birth-control pill was wrong and should be discounted, say scientists with the landmark Women’s Health Initiative, whose database was used for the study.

The report was front-page news across the U.S. in October with its conclusion that using the pill cuts the risk of heart disease, heart attack, stroke and certain types of cancer later in life. This came as a surprise to many women who’d heard the contrary from their own doctors for decades.

It came as an even bigger surprise to the group of Seattle scientists responsible for collecting the data upon which the study was based.

Epidemiologist and statistician Ross Prentice nearly spit out his cereal when he saw The Associated Press report in The Seattle Times: Researchers at Wayne State University in Detroit were using Women’s Health Initiative data to overturn the common wisdom on the pill.

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Prentice is the chief number cruncher for the health initiative and this was news to him. His team at Seattle’s Fred Hutchinson Cancer Research Center gathers and analyzes the data on more than 160,000 women. It’s the biggest women’s health study ever done and best-known for showing that the risks of hormone-replacement therapy outweigh its benefits. Prentice knows the database better than anyone and did not believe it could bear out such sweeping conclusions about the pill. First of all, the data were collected on women 50-79 years old — many of whom would have been around 40 when the pill hit the market.

So he and his colleagues reanalyzed the numbers to verify the Wayne State findings. They found that the association between the pill and a lower incidence of disease was really a factor of age. The older the women, the more health problems they were likely to have, and the less likely they were to have used oral contraceptives.

“When you’re comparing a 79-year-old women who never used oral contraceptives to a 62-year-old woman who did, the age difference is much more likely to explain things than who used the pill,” said Garnet Anderson, a biostatistician at Fred Hutch who helped examine the data.

Dr. Rahi Victory and his co-authors at Wayne State, Dr. Susan Hendrix and Dr. Michael Diamond, did take age into consideration, but Prentice said they didn’t control for it adequately. They also did not get authorization or input from the health initiative, as is customary, before presenting their data at the annual meeting of the American Society for Reproductive Medicine on Oct. 20, he said. The authors did not return calls requesting a comment.

The vice president of research at Wayne State, John Oliver, said the findings presented at the meeting were preliminary. The study has not yet gone through the peer-review process, which is standard for scientific publications. “I suspect it made a bigger splash than they anticipated,” he said.

Anderson said the Women’s Health Initiative data isn’t a good source to answer such questions about the birth-control pill because it enrolled mostly healthy women and was designed to look forward, not backward. Women who, for instance, had been on the pill and had a serious stroke, heart attack or died would never have been included in the study.

She urges women to disregard the Wayne State findings.

A separate survey by the Centers for Disease Control and Prevention earlier this week found that 82 percent of women aged 15 to 44 had used the pill at some point. Like hormone-replacement therapy, which is taken after menopause, most birth-control pills contain a combination of the hormones estrogen and progestin.

Past studies have produced cautions about the birth-control pill — that it increases the risk of heart attack, stroke, blood clots and certain types of cancer. Those warnings still stand, Anderson emphasized.

Julia Sommerfeld: 206-464-2708 or jsommerfeld@seattletimes.com