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Home > Understanding Breast Cancer > Risk Factors and Prevention > Breast Cancer Risk Factors Table

  


Breast Cancer Risk Factors Table

 

The table below lists factors that are linked (or in some cases, not linked) to breast cancer. It also lists many factors that are still under study. Factors are grouped based on the strength of the scientific evidence, including:  

  • Established and probable factors have the strongest evidence behind them and are recognized as linked (or not linked in some cases) to breast cancer. 
     
  • Possible factors have less evidence behind them. They suggest links to breast cancer but need more study before solid conclusions can be made. 
     
  • Insufficient or inconsistent factors are backed by few studies or the studies to date show very mixed results, which don't allow comment on any potential link with breast cancer. 

Click on any of the factors to learn more.  

 

Established and Probable Factors

Recognized as linked (or not linked in some cases) to breast cancer.   

 Legend 
 

Increases breast cancer risk 

 

Decreases breast cancer risk 

 

Not related to breast cancer risk (neither increases nor decreases risk)

  

Increases breast cancer risk 
(Listed alphabetically.) 

African American ethnicity 

Breast density (high)  

Age (older) 

Family history of breast cancer  

Age at first childbirth (older) 

Height (taller)  

Age at first period (younger) 

Hyperplasia (benign breast condition) 

Age at menopause (older) 

Light at night and shift work  

Alcohol 

Lobular carcinoma in situ (LCIS) 

Ashkenazi Jewish heritage 

Menopausal hormone therapy - estrogen + progestin  

Being female 

Overweight after menopause  

Birth control pills 

Personal history of cancer  

Blood androgen levels (high) 

Prolactin hormone levels (high)  

Blood estrogen levels (high) after menopause 

Radiation exposure from medical imaging  

Bone density (high) 

Radiation treatment during youth  

BRCA1 or BRCA2 gene mutation 

Weight gain after menopause 

Decreases breast cancer risk 
(Listed alphabetically.) 

Breastfeeding 

Fruits and vegetables  

Carotenoids 

Overweight before menopause 

Exercise (physical activity) after menopause 

 

Not related to breast cancer risk (neither increases nor decreases risk) 
(Listed alphabetically.)  

Abortion 

Electromagnetic fields (from utility wires, electric blankets, etc.) 

Blood organochlorine levels (exposure to certain types of pesticides and industrial chemicals) 

Exercise (physical activity) before menopause 

Bras or underwire bras 

Hair dyes and hair relaxers 

Breast implants 

Left-handedness 

Caffeine 

Menopausal hormone therapy - estrogen only (use less than 10 years) 

Cell phone use 

Trauma to the breast 

Deodorant/antiperspirant use 

Weight gain before menopause 

 

Possible Factors

Recognized as potentially linked (or not linked in some cases) to breast cancer, but need more study before solid conclusions can be made. These factors are still under study.   

 Legend 
 

Increases breast cancer risk 

 

Decreases breast cancer risk 

 

Not related to breast cancer risk (neither increases nor decreases risk)

 

Increases breast cancer risk
(Listed alphabetically.)  

Blood estrogen levels (high) before menopause 

Meat consumption before menopause  

IGF-1 hormone levels (high) before menopause 

Smoking  

Decreases breast cancer risk
(Listed alphabetically.)

Vitamin D 

 

Not related to breast cancer risk (neither increases nor decreases risk)
(Listed alphabetically.)  

Aspirin 

Glycemic index and insulin 

Dairy products 

IGF-1 hormone levels (high) after menopause 

Dietary fat 

Meat consumption after menopause 

Fertility drugs 

Soy 

 

Factors with inconsistent results or insufficient evidence

For these factors, there are few studies or study results are very mixed. More research is needed to comment on any potential link to breast cancer.

(Listed alphabetically.)  

Acrylamide (found in foods such as French fries) 

Folic acid (folate) and multivitamin use 

Antibiotic use 

Migraine headaches 

Birthweight (a person's weight at birth)  

Parabens (found in some body care products and cosmetics)  

Breast size 

Plastics 

Breastfed as an infant 

Secondhand smoke exposure 

DES (in utero exposure and breast cancer risk among offspring) 

Stress 

 

Where do the data come from?

Human studies

The data in this table come from two main types of research studies:

The goal of these studies is to give information that helps support or disprove an idea about a possible link between an exposure (like alcohol use) and an outcome (like breast cancer) in people. Although they have the same goal, observational studies and randomized controlled trials differ in the way they are conducted and in the strength of the conclusions they reach.  

Learn more about different types of research studies.

Animal studies

Animal studies add to our understanding of how and why some factors cause cancer in people. However, there are many differences between animals and people that make it hard to translate findings directly from one to the other. Animal studies are also designed differently than human studies. They often look at exposures in larger doses and for shorter durations than are suitable for people. Thus, animal studies can lay the groundwork for research in people, but in order to draw conclusions for people, we need human studies.  

All data presented within the Understanding Breast Cancer section of this website come from human studies unless otherwise noted.

Finding information on risk factors for breast cancer

Some organizations conduct research and/or prepare summary reports of research on certain exposures shown to have a link (or no link) to breast and other types of cancer. These agencies are a good place to find detailed, up-to-date information (for example, if you have concerns over a news item on cancer).

IARC is a part of the World Health Organization. The CDC, NTP and FDA are all part of the U.S. Department of Health and Human Services. 

To learn more about the role of the environment in breast cancer, Komen sponsored a study from the Institute of Medicine, "Breast Cancer and the Environment, a Life Course Approach." A culturally appropriate, related Question and Answer booklet on breast cancer and the environment is also available in Spanish.

Updated 01/28/14

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