Early Life Exposures and Breast Cancer Risk
Most research on risk factors for breast cancer has focused on exposures and behaviors that occur during adulthood.
There’s a lot of interest in how events early in life may affect adult breast cancer risk [618-619]. These include factors related to the prenatal environment, infancy, childhood and adolescence (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.
Timing of exposures may impact breast cancer risk
Researchers are studying how the timing of certain factors may be related to breast cancer risk.
Some exposures and behaviors can occur throughout life (such as weight gain). 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 not be related to breast cancer risk when the exposure occurs in adulthood, but they may be linked to an increase or decrease in risk when the exposure occurs during childhood or the teen years.
Why might timing matter?
Some in utero (in the womb) and early life exposures may affect the way the body develops and be linked to 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 [13,17,19-21,620-622].
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 [618-619].
Although it’s not fully known how (and which) early life exposures may be related to breast cancer risk in adulthood, these topics are under study.
A better understanding of these exposures may improve our understanding of breast cancer biology and how breast cancer develops later in life.
In utero (in the womb) exposures and factors related to birth and infancy
In utero exposures
In utero exposures under study for possible links to breast cancer (in the adult daughters of women exposed during pregnancy) include:
- Certain chemicals that may have estrogen-like effects in the body
- Diethylstilbestrol (DES), a drug now banned, but given to some pregnant women before 1970
Weight gain during pregnancy is also under study as a possible breast cancer risk factor in the adult daughters of women who gained weight during pregnancy.
Factors related to birth and infancy
Birthweight (a woman’s weight when she was born) is related to breast cancer risk [55-61,79]. Studies show women with a higher birthweight have an increased risk of breast cancer, especially before menopause [55-61].
Other factors related to a woman’s birth and infancy are under study for possible links to breast cancer. These include:
- Birth length (a woman’s height at birth)
- Breastfed as an infant (being breastfed)
There are too few studies on these topics to draw conclusions about possible links to breast cancer.
Exposures in childhood and the teen years
Age at first menstrual period
Age at first menstrual period is a known risk factor for breast cancer. Starting periods at a young age is linked to a small increase in breast cancer risk [13,17,19-21].
Learn more about age at first menstrual period and breast cancer risk.
Height and weight
Height and weight in childhood and the teen years may be related to breast cancer risk [55,187,623].
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) [55].
Women who were heavy as children and teens may have a lower risk of breast cancer than women who were thin in their youth [55,187,624-628].
However, being heavy during childhood and the teen years is not advised as it’s linked to an increased risk of heart disease and many other health conditions in adulthood [629].
Learn about adult height and breast cancer risk.
Learn about adult weight, weight gain and breast cancer risk.
Diet
Some studies suggest a healthy diet as a teen may be linked to a lower risk of breast cancer 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 [171,425,619,630].
Some findings suggest women who ate a high-fat diet during the teen years may have an increased risk of breast cancer [425]. Other findings suggest women who ate a lot of red meat during the teen years may have an increased risk of breast cancer before menopause [478].
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 teens and those who ate less soy as teens [506,508,631-632].
Some studies have looked at milk intake during the teen years. A meta-analysis that combined the results from 7 studies found no difference in breast cancer risk among women who drank more milk as teens and those who drank less milk as teens [425].
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.
Learn more about diet and breast cancer.
Alcohol
Some studies suggest women who drank alcohol in their teen years (up until the age at first pregnancy) may have an increased risk of breast cancer in adulthood [633-635].
For example, one large study found for every 6-7 alcoholic drinks a woman consumed each week between the age when she started her period and the time of her first pregnancy, her breast cancer risk increased by 10% [633].
Learn more about alcohol use in adulthood and breast cancer risk.
Exercise (physical activity)
Study findings on exercise during childhood and the teen years and a woman’s breast cancer risk later in life are mixed [142-143].
Some findings show women who were more active as children and teens may have a lower risk of breast cancer compared to women who were less active as children and teens [142].
Other findings show women who were physically active during childhood and the teen years may have a slightly decreased risk of breast cancer before menopause, but not after menopause [143].
More research is needed to draw conclusions about a possible link between exercise during childhood and the teen years and breast cancer risk.
Learn about exercise in adulthood and breast cancer risk.
Smoking
Women who start smoking early in life (especially before a first pregnancy) and continue smoking in adulthood appear to have an increased risk of breast cancer [312-313,316,318,320].
Learn about smoking in adulthood and breast cancer risk.
Hair dye use
One study looked at women’s use of hair dye when they were between 10 and 13 years old and whether it was linked to breast cancer risk when they were adults. It found no increased risk of breast cancer among women who used hair dye between the ages of 10 and 13 [469].
Learn about hair dye use in adulthood and breast cancer risk.
Updated 04/25/24