If women and girls adopted healthier behaviors and the women with highest risk took preventive medicine like tamoxifen, the researchers say half of breast cancer cases might be avoided, reports Newsmax Health.

"We really need to go back and work at breast cancer prevention starting at a young age," Dr. Graham Colditz, associated director for prevention and control at Siteman Cancer Center and Washington University, told Reuters Health.

Colditz and his Washington University colleague Dr. Kari Bohlke argue that more emphasis should be on using what's already known about what raises breast cancer risk. For instance, just a small fraction of women who could benefit from the breast-cancer-preventing medications tamoxifen and raloxifene actually take them, the researchers note in their report.

Nevertheless, they add, women can slash their breast cancer risk by avoiding alcohol or drinking very moderately; maintaining a healthy weight; being physically active; eating plenty of fruits, vegetables and whole grains; and, if they have children, breastfeeding them.

The risk associated with lifestyle factors begins to accumulate in early life, the researchers point out, and there is evidence that the time between a girl's first period and her first pregnancy may be particularly important in determining breast cancer risk.

For example, research has found that teens who don't drink alcohol at all may reduce their future risk of breast cancer by 20 percent to 30 percent compared to their peers who had at least one drink in the past 30 days.

And young adult women who drink less than one drink a day have a 20 percent to 30 percent lower risk than their peers who drink at least four drinks a week.

Young people who eat plenty of fruits, vegetables and whole grains are already reducing their future risk of several types of cancer - including breast cancer, according to the analysis.

Physical activity has the most breast-cancer-preventing benefit when women sustain it throughout their lifetimes, according to Dr. Colditz, but "it's never too late to start," he said.

Being obese after menopause is a key risk factor for breast cancer, he noted, but women who are able to lose weight in their post-menopausal years will bring down their risk of the disease.