Women who take six steps including limiting exposure to medical radiation and adopting a healthy lifestyle may reduce their risk for breast cancer, but there's little evidence avoiding certain chemicals makes a difference, says a new report on environmental factors.

The report from the Institute of Medicine, an independent organization based in Washington, D.C., that advises the U.S. and Canadian governments, assesses the breast cancer risk from environmental factors and advises on actions people can take to potentially reduce the risk for the disease.

The report's authors recommend six steps they concluded had consistent scientific evidence:

• Avoiding unnecessary medical radiation such as diagnostic CT scans.
• Forgoing use of combination estrogen-progestin hormone therapy post-menopause if possible.
• Limiting alcohol.
• Maintaining a healthy weight.
• Exercising regularly.
• Avoiding tobacco use.

The committee used a broad definition of "environment" that included all factors not directly inherited through DNA. That included what's in the air and water, diets, use of vitamins and factors such as working night shifts.

For other environmental factors, it was harder to tell because the evidence wasn't as strong, they said.

The evidence indicated a "possible, though currently less clear," link to increased risk for breast cancer from exposure to benzene, 1,3-butadiene and ethylene oxide — chemicals found in some workplace settings and in gasoline fumes, vehicle exhaust and tobacco smoke.

Some substances were considered unlikely to affect a woman's risk of breast cancer. Several studies found no connection between avoiding personal use of hair dyes and non-ionizing radiation emitted by mobile devices and other technologies and breast cancer, the panel said.

For other chemicals, the evidence was insufficient or contradictory. The plasticizer bisphenol A (BPA), pesticides, ingredients in cosmetics and dietary supplements fell into that category.

Exposures early in life

"We don't have enough data to say 'toss your water bottles,"' said committee chair Irva Hertz-Picciotto, chief of environmental and occupational health at the University of California, Davis.

Part of the problem in assessing the environmental risks for breast cancer is that most research has focused on adults and the few years before a diagnosis, but recent studies suggest that exposure earlier in life, including prenatally, are important, the report's authors said.

Laura Anderko, a public health scientist at Georgetown University Medical Center in Washington, DC, said she was "deeply disappointed" by the report's heavy emphasis on personal responsibility for cancer prevention.

"It is in stark contrast to the President's Cancer Panel report last year that has a strong call to action on chemical policy reform," Anderko wrote in an email to Associated Press.

The report was presented at the San Antonio Breast Cancer Symposium in Texas on Wednesday.

It was sponsored by Susan G. Komen for the Cure.

With files from The Associated Press