Most research on risk factors for breast cancer has focused on exposures and behaviors that occur during adulthood.
However, there is growing interest in how events early in life may affect adult breast cancer risk [517-518]. These include factors related to the prenatal environment, infancy, childhood and the teen years (adolescence).
Researchers are studying how the timing of certain factors may impact breast cancer risk.
Some exposures and behaviors can occur throughout life (such as weight gain). Researchers are learning that some of these factors may impact breast cancer risk differently when they occur early in life versus when they occur in adulthood. For these factors, risk may depend on the timing of the exposure.
For example, some factors may have no impact on breast cancer risk when the exposure occurs in adulthood, but they may increase or decrease risk when the exposure occurs in childhood or the teen years.
Breast cancer in children, teens and young adults is very rare. The interest in early life exposures relates to breast cancer in adults, not in younger people.
Some in utero (in the womb) and early life exposures may affect the way the body develops and impact breast cancer risk later in life.
For example, girls with a low birthweight may begin menstrual periods at younger ages than other girls, and having a younger age at first period is linked to an increased risk of breast cancer [7,519-521].
During puberty, hormones in the body cause the breasts to grow. This time of growth, when breast cells are dividing, may be a time when the breast tissue is vulnerable to certain exposures [517-518].
Although it's not fully known how (and which) early life exposures may impact breast cancer risk in adulthood, these topics are under active study.
A better understanding of exposures may improve our understanding of breast cancer biology and how breast cancer develops later in life.
In utero exposures under study for possible links to breast cancer (in the grown daughters of women exposed during pregnancy) include:
Factors related to a woman’s birth and infancy that are under study for possible links to breast cancer include:
At this time, there are too few studies on these topics to draw conclusions about possible links to breast cancer risk.
Age at first period is a known risk factor for breast cancer. Starting menstrual periods at a young age is linked to a small increase in breast cancer risk .
Learn more about age at first period and breast cancer risk.
Height and weight in childhood and the teen years may be related to breast cancer risk.
For example, women who were taller at ages 8 and 14 (and those who grew the most in height from ages 8-14) may have a higher risk of breast cancer than women who were shorter (and who didn’t grow as much in height) .
Women who were heavy as children and teens may have a lower risk of breast cancer than women who were thin in their youth [522-526].
However, being heavy during childhood and the teen years is not advised as it increases the risk of heart disease and many other health conditions in adulthood .
Learn how adult height affects breast cancer risk.
Learn how adult weight and weight gain affect breast cancer risk.
Some studies suggest a healthy diet as a teen may lower breast cancer risk in adulthood.
For example, early findings suggest women who ate diets high in fiber, fruits, vegetables or nuts when they were teens may have a decreased breast cancer risk compared to women who did not [518,528-530].
Some findings suggest eating a high-fat diet during the teen years may increase breast cancer risk . Other findings suggest eating a diet high in red meat during the teen years may increase the risk of breast cancer before menopause .
Several large studies have looked at soy intake during the teen years among Asian women and Asian-American women. Findings to date show no difference in breast cancer risk among women who ate more soy as teenagers and those who ate less soy [531-534].
More research is needed to draw conclusions about possible links between diet during the teen years and breast cancer risk.
Learn about healthy diet in adulthood and breast cancer risk.
Some studies suggest exercise during the teen years may affect a woman’s breast cancer risk later in life.
One large study found that exercising as a teen did not impact breast cancer risk after menopause .
However, women who got more physical activity when they were teenagers had a slightly lower risk of breast cancer before menopause compared to women who got less activity as teens .
More research is needed to draw conclusions about possible links between exercise during the teen years and breast cancer risk.
Learn about exercise in adulthood and breast cancer risk.