It’s often said that the habits we form in our formative years will affect our lives later in life. As trite as that phrase has become, it’s nevertheless a phrase whose cup runneth over with truth. Case in point: this latest study.

According to researchers from the Washington University School of Medicine in St. Louis, Missouri, women who exercised regularly while teenagers have a nearly 25 percent reduced risk of developing breast cancer later in life. Their findings are published in the Journal of the National Cancer Institute.

Researchers came to this finding after assessing the health histories of approximately 65,000 women (all in the nursing profession) between the ages of 24 and 42 (no one had been diagnosed with breast cancer at the study’s outset). For the next six years, the researchers would stay in touch with the ladies, keeping track of their health and their daily exercise habits. But before they did this, they asked each of the participants what their exercise habits were like while they were young.

At the conclusion of the six-year study, the researchers found one particularly overriding commonality among the group of women: those women who exercised for at least 3 ¼ hours per week in their teenage years were 23 percent less likely to develop breast cancer in the six-year study period, whether that exercise was more labor intensive than time intensive (such as running) or time intensive rather than labor intensive (other women exercised for as much as 13 hours per week but through less labor-intensive means, like walking).

The researchers can’t be certain what it is about exercise that seems to shield women from developing breast cancer, other than to re-state the obvious: that regular exercise now affects long-term health later.

This research piggybacks on some testing done previously which showed that middle-aged women who exercised regularly were also at a reduced risk for developing breast cancer when compared to those who didn’t exercise regularly. This and the latest study go back to my original statement about one’s habits when young and their impact on later in life: the things that one does in his or her teenage years sticks with them as they grow older. Exercise is no exception. I was an exercise fiend when I was younger; today, my zealotry has not diminished one iota.

Are there exceptions to this rule? Of course! There’s virtually no generalization without an exception (that’s why they’re called generalizations). I know people who ran track in high school but today are about as big as the buses that carried them to and from track meets! So yes, there are exceptions.

But generally speaking, healthy habits like exercise are hard habits to break, and depending on how healthy their exercise habit is at its formation (i.e. exercise addiction is counterproductive, and often leads to a disdain for all things exercise due to burn out or injury) determines what kind of diseases they may encounter later in life. And with breast cancer the leading cause of cancer deaths among women (excluding skin cancers), the importance of exercise has never been more important than it is today (Here’s a Did You Know?: The rate of breast cancer has increased from 1 in 20 women in 1960 to 1 in 8 women in 2008).