In a study likely to add to the debate over when and how often to screen for breast cancer, Swedish researchers said on Wednesday that women aged 40-49 who got regular mammograms were 29 percent less likely to die of the disease.

Their study of 600,000 Swedish women, followed for 16 years, suggests that even younger women benefit from mammograms.

“The number needed to screen to save one life was 1,250,” Dr. Hakan Jonsson of Umea University told reporters in a telephone briefing.

Jonsson and colleagues compared women living in counties in Sweden that invited women aged 40 to 49 for a mammogram to women living in counties that did not. They looked to see who actually did get a mammogram, and then checked records from 1986 to 2005.

Each county was different and the women were screened on average every 18 months to two years.

Overall, 523 of the women who got mammograms died of breast cancer, compared to 1,205 women who did not get screened, they reported in the journal Cancer. The results were also scheduled to be presented to a breast cancer meeting sponsored by the American Society of Clinical Oncology.

“Though consensus has been reached that mammography screening can reduce mortality for women aged 50 to 69, the effectiveness for women aged 40 to 49 is still questioned,” Jonsson’s team wrote.

They were unable to account for women who may have gone to private doctors for mammograms.

The issue is hotly debated, and important for insurance companies and national health systems trying to save lives but also trying to get good value for money spent.

Breast cancer is the most common cancer in women worldwide. It kills around 465,000 people globally each year.

Mammograms can catch cancer early, when it is easier to treat, but it is not clear this translates into longer lives for patients.

Just last week Norwegian researchers said routine mammograms were less effective at preventing cancer deaths than expected. They said inviting women aged 50 to 69 to have routine mammograms and offering them better care from a team of experts helped cut the breast cancer death rate by 10 percent.

In November, the U.S. Preventive Services Task Force caused a firestorm by recommending that the test be taken every other year instead of every year for women 50 to 74.

In May, researchers reported in the Journal of the National Cancer Institute that mammograms detect few cancers in women under the age of 40 but cause expense and anxiety because women frequently get “false positives.”

Dr. Daniel Kopans, a professor of radiology at Harvard Medical School who frequently weighs into the mammogram debate, said the latest Swedish study showed women should be screened starting at 40, as recommended by the American Cancer Society.

“The age of 50 has never had any scientific or biological basis. Data have been used, inappropriately, to make it appear as if something changes abruptly at the age of 50, when the data, actually, do not show any sudden changes in the parameters of screening at the age of 50, or any other age,” Kopans said in a statement.

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By Maggie Fox

WASHINGTON, Sept 29 (Reuters)