Medical radiation from CT scans, being overweight, using combination estrogen and progestin hormone therapy and drinking alcohol were among the usual suspects deemed to have the most convincing evidence showing a link with breast cancer risk, according to a new report by the Institute of Medicine examining environmental factors that contribute to the disease.

In a supplement, the group noted that avoiding "inappropriate medical radiation exposure" was a workable risk-reduction goal, even though it also said that it should be balanced against the offsetting risk: missing crucial medical information by skipping a scan.

IOM said it prepared the report, Breast Cancer and the Environment: A Life Course Approach, at the behest of Susan G. Komen for the Cure.
Breast cancer is the most common cancer in American women, and 230,000 new diagnoses are expected to be made this year, IOM said.

Other factors suggestive of cancer risk but where the evidence is "less persuasive" include working the graveyard shift, exposure to secondhand smoke and breathing in a cocktail of chemicals released when pumping gas.

The group, famous for revolutionizing health care safety with its 2000 report "To Err Is Human," said there wasn't enough evidence to gauge whether some chemicals, such as the plastic softener BPA, a potential endocrine disruptor, upped a women's cancer risks. However, the group, chaired by Irva Hertz-Picciotto, a professor with University of California Davis, did say they were able to rule out some long-feared factors, such as non-ionizing radiation generated by microwaves and mobile phones, as "multiple studies have found no connection to the disease."

But women will find that it won't necessarily be easy to meaningfully apply all this information, especially as it deals with, in general, studies that measure modest changes in risks over large populations. And the harms of some activities or environmental exposures are sometimes balanced out by benefits. For instance, in a question and answer supplement accompanying the report, the group noted that while drinking one glass of wine or beer a day is linked with a slightly increased cancer risk, it's also linked with decreased risk of heart disease.

"This is an example of how complicated it can be to decide what is good for you," IOM said. "Each individual woman needs to consider how the benefits and risks of alcohol may apply to her."

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