The Who, What, Where, When and Sometimes, Why.

Factors Under Study

Many possible risk factors for breast cancer are under study.

Though the findings to date are not strong enough to say whether these factors are truly related to breast cancer, research suggests they call for further study.

A full list of factors under study for possible links to breast cancer is too long to present here. The factors below have been studied more than most or they’ve gotten a lot of media attention.

Our Breast Cancer Risk Factors Table compares factors by level of risk and strength of evidence.

The factors below are listed alphabetically.

French fries and other foods cooked at high temperatures contain a chemical called acrylamide. Coffee also contains acrylamide.

Studies, including a meta-analysis that combined the results from 8 studies, have found no link between consuming foods and beverages that contain acrylamide and breast cancer risk [352-356,614].

However, this topic is still under study.

Learn more about diet and breast cancer.

Anti-Müllerian hormone (AMH) is produced in the ovaries. It’s important in the development of reproductive organs.

Blood levels of AMH peak around age 20-25, then decline as a woman gets closer to menopause [357]. After menopause, AMH is no longer detectable [357].

Women with higher blood levels of AMH may have a higher risk of breast cancer compared to women of the same age who have lower levels of AMH [357-359].

Why might AMH blood levels be related to breast cancer risk?

Higher AMH levels may reflect some reproductive events. For example, women with higher blood levels of AMH are more likely to have a later age at menopause than women with lower AMH levels [360].

Having a later age at menopause increases breast cancer risk [10,16,20]. This increased risk is likely due, at least in part, to the amount of estrogen a woman is exposed to in her life. A higher lifetime exposure to estrogen is related to an increase in breast cancer risk [19].

More research is needed to draw conclusions about a possible link between blood levels of AMH and breast cancer risk.

Findings on a potential link between antibiotics and breast cancer risk are mixed.

Some studies have found the use of antibiotics increases breast cancer risk, while others have found no link between the two [361-366]. The authors of one study reported the increase in breast cancer risk could be explained by other factors [368].

The only cohort study done found a weak increase in risk, but only among premenopausal women using long-term antibiotics to treat urinary tract infections [361].

More research is needed to draw conclusions about a possible link between antibiotic use and breast cancer risk.

Most studies, including a meta-analysis that combined the findings from 4 cohort studies, have found no link between anti-depressant use and breast cancer [367-370].

However, this topic is still under study.

 

Findings on a potential link between aspirin use and breast cancer have been mixed.

Some studies, including 3 meta-analyses, have found a slight decrease in risk with regular aspirin use [371-374].

However, another meta-analyses and some cohort studies have found no difference in risk between women who took aspirin regularly compared to those who did not [373,375-379].

Also, findings from a randomized controlled trial found no difference in breast cancer risk among women who took aspirin every other day for 10 years compared to those who took a placebo [380].

More research is needed to draw conclusions on a possible link between the use of aspirin and other non-steroidal anti-inflammatory drugs (NSAID) and breast cancer risk. 

A possible link between aspirin use and increased breast cancer survival is also under study [381].

Findings on a potential link between breast size and breast cancer are mixed.

Some studies have found having a larger breast size increases risk, while others have found no link between breast size and risk [383-387].

Two studies have found breast size increases risk among thin women, but not among heavy women [384-385].

More research is needed to learn whether or not breast size is linked to breast cancer risk. 

Researchers are studying whether having been breastfed as an infant is linked to a lower risk of breast cancer.

Most large studies have found no difference in breast cancer risk between women who were breastfed as an infant and women who were not breastfed [387-391].

There are too few studies on this topic to draw conclusions.

Data on other early life exposures are also limited.

Learn about other early life exposures and breast cancer risk.

Learn about breastfeeding and the risk of breast cancer in mothers

 

Dairy products are under study as a factor that may:

  • Increase breast cancer risk
  • Decrease breast cancer risk

Some researchers have suggested the high fat content in many dairy products or traces of pesticides or growth hormones in milk may increase risk [392-393].

Others have studied whether the calcium and vitamin D in dairy products may protect against breast cancer [390,394].

Learn more about diet and breast cancer.

Dairy products and breast cancer risk after menopause

Large cohort studies and a pooled analysis of data from more than 20 studies have found no link between consuming dairy products (including milk, cheese and yogurt) and breast cancer risk after menopause [395-398].

It appears unlikely dairy products are related to breast cancer after menopause.

Dairy products and breast cancer risk before menopause

Most studies have found no link between consuming dairy products and breast cancer risk before menopause [396-399].

However, data from a large cohort study found women who ate a lot of high-fat dairy products (such as whole milk or butter) had an increased risk of breast cancer before menopause [399].

More research is needed to confirm these findings.

Consuming dairy products during the teenage years or early adulthood

Large cohort studies have found no link between eating or drinking dairy products during the teen years or early adulthood and the risk of breast cancer (before or after menopause) [400-401].

This topic is under study.

Learn about other early life exposures and breast cancer risk.

For a summary of research studies on dairy products and breast cancer, visit the Breast Cancer Research Studies section.  

Some exposures to women during pregnancy (in utero) have been suggested as risk factors for breast cancer among their offspring.

Diethylstilbestrol (DES) was a drug with estrogen-like traits. It was given to women to prevent pregnancy problems until about 1970. DES was taken off the market because it was shown to increase the risk of vaginal cancers in daughters of women who took the drug.

There’s some concern DES might also increase the risk of breast cancer among daughters of women who took the drug during pregnancy.

Studies to date of women exposed to DES in utero have had mixed findings. Some studies have found an increased risk of breast cancer compared to women not exposed to DES in utero, while others have found no excess risk for these women [402-406]. 

This topic is under study.

Data on other in utero exposures are limited. 

Learn about other early life exposures and breast cancer risk.

Women with type 2 diabetes may have an increased risk of breast cancer after menopause [71-73,407]. There doesn’t appear to be an increased risk before menopause [71]. 

The reasons behind a possible link between diabetes and breast cancer after menopause are unclear. It may be related to high levels of insulin in women with type 2 diabetes.

Insulin is a hormone that controls blood sugar levels. It’s released by the pancreas after a meal.

Women with other conditions related to high levels of insulin (such as hyperinsulinemia) may also have an increased risk of breast cancer after menopause [408-412].

These issues are under study.

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Komen Perspectives

Read our perspective on diabetes and breast cancer.*

*Please note, the information provided within Komen Perspectives articles is only current as of the date of posting. Therefore, some information may be out of date.

Most studies have shown no link between a high-fat diet in adulthood and an increased risk of breast cancer [413-419].

However, the type of fat, rather than the total amount of fat, may be related to breast cancer risk [413-414,417,419].

This topic is under study.

Learn more about diet and breast cancer.

High-fat diet during the teenage years

Eating a high-fat diet during the teenage years (adolescence) may play a role in breast cancer.

Findings from a large cohort study showed women who ate a diet high in total fat when they were teens had an increased risk of breast cancer before menopause compared to women who ate a diet low in fat as teens [400].

For a summary of research studies on dietary fat and breast cancer, visit the Breast Cancer Research Studies section

Fertility drugs stimulate the ovaries, causing estrogen levels in the body to increase. Because high estrogen levels are linked to breast cancer risk, it’s been suggested the use of fertility drugs might increase risk.

Most studies, including a meta-analysis of 20 studies on the fertility drug clomiphene (Clomid) and 22 studies on other types of fertility drugs, have found no link to breast cancer [420-427].

Some findings with 10 or more years of follow-up suggest fertility drug use may modestly increase breast cancer risk [424]. However, 2 studies with 20-21 years of follow-up found no increased breast cancer risk among women who used fertility drugs [425,427].

Although most studies show fertility drugs do not increase breast cancer risk, more studies with long-term data are needed to confirm these findings.

Learn more about estrogen and breast cancer risk

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Komen Perspectives

Read our perspective on fertility drugs and breast cancer risk.*

*Please note, the information provided within Komen Perspectives articles is only current as of the date of posting. Therefore, some information may be out of date.

Folate is a vitamin found in many fruits and green leafy vegetables. Folic acid (the supplement form of folate) is also added to some breakfast cereals, breads and many multivitamins.

Folate is important in copying and repairing DNA.

Getting enough folate may make it more likely that DNA is copied correctly when cells divide. This in turn may make it less likely cells become cancerous. For this reason, folic acid and multivitamins have been studied to see if they might lower the risk of breast cancer.

Most studies (including 3 meta-analyses) have found no link between blood levels of folate, eating a diet high in folate, taking a folic acid supplement or taking multivitamins and breast cancer risk [428-436].

However, these topics are still under study. 

Learn more about diet and breast cancer.

Some have suggested eating meat may increase the risk of breast cancer. Possible reasons include increased fat intake, exposure to chemicals formed when cooking meat at high temperatures and exposure to hormones in meat [393,437].

Most studies, including 2 pooled analyses, have found no link between total meat intake (or red meat intake) and breast cancer risk [397,439-440].

However, some findings show women who eat a lot of processed meats (such as sausage and bacon) may have an increased risk of breast cancer [438-440].

Learn more about diet and breast cancer.

Eating meat during the teen years

Some findings suggest eating a lot of red meat during the teen years may increase the risk of breast cancer before menopause [441].

However, more study on this topic is needed.

Eating well done or overcooked meat

Studies have looked at whether eating well done or overcooked meat is linked to an increased risk of breast cancer. Some studies have found a link, while others have not [438,442-444].

Eating well done or overcooked meat and survival after a breast cancer diagnosis is also under study [445].

For a summary of research studies on meat consumption and breast cancer, visit the Breast Cancer Research Studies section

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Komen Perspectives

Read our perspective on meat consumption and breast cancer risk.*

*Please note, the information provided within Komen Perspectives articles is only current as of the date of posting. Therefore, some information may be out of date.

Some early findings suggest women who have a lot of moles on their bodies may have a higher risk of breast cancer than women with few moles [447-448].

The reasons behind a possible link are not yet clear.

However, a high number of moles may be a marker of increased levels of estrogen and testosterone in the body [449]. Increased levels of these hormones are linked to an increased risk of breast cancer [19].

More research is needed before conclusions can be made about a possible link between moles and breast cancer risk.

Learn more about estrogen and breast cancer risk.

Learn more about testosterone (and other androgens) and breast cancer risk.

Parabens are chemical preservatives found in some cosmetics and body care products. They may be found in some make-up, lotion and shampoo, as well as in foods and medicines. (Most deodorants and antiperspirants don’t contain parabens.)

Parabens have been shown to have very weak estrogen activity. Animal studies have found some health effects of parabens, but only in very large doses [450-451].

The Cosmetics Ingredient Review Expert Panel conducts research on product safety for the U.S. Food and Drug Administration (FDA).

In 2008, the Panel first concluded paraben exposure from cosmetics and body care products was safe [451]. In 2012, 2017 and again in 2018, the Panel looked at newer data and concluded paraben exposure from these products was safe [452-454].

The Panel found the estrogen effects from parabens are so weak it’s highly unlikely they can be harmful to health, especially in the small amounts used in cosmetics and body care products [451-454].

The Panel also noted parabens don’t build up in the body over time, so they’re unlikely to cause harm [451-454].

However, this topic is still under study.

Find more information from the FDA on the safety of products containing parabens.   

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Komen Perspectives

Read our perspective on body care products containing parabens and breast cancer risk.*

*Please note, the information provided within Komen Perspectives articles is only current as of the date of posting. Therefore, some information may be out of date.

Plastics

Links between plastics and cancer are often reported by the media and in social media and other hoaxes (one e-mail hoax falsely claims to be a study from Johns Hopkins University).

However, there’s no scientific evidence supporting a link between using plastic items (such as drinking water from a plastic bottle) and the risk of breast cancer.

Bisphenol A (BPA)

BPA is a chemical found in some plastic containers for food and beverages. The U.S. Food and Drug Administration (FDA) studies possible health effects from BPA.

Small amounts of BPA from the containers can get into the food and beverages inside. As a result, we can be exposed to low levels of BPA [455]. However, BPA doesn’t build up in the body over time, so it’s unlikely to cause harm [455].

There’s no evidence to suggest a link between BPA and breast cancer risk [456-459].

The FDA continues to study BPA and health.

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Komen Perspectives

Read our perspective on plastics containing bisphenol A (BPA) and breast cancer risk.*

*Please note, the information provided within Komen Perspectives articles is only current as of the date of posting. Therefore, some information may be out of date.

Most large cohort studies have found no link between breathing secondhand smoke (the smoke from other people’s cigarettes), also called passive smoking, and breast cancer risk [460-465].

However, findings from some case-control studies and one large cohort study have shown a slightly increased risk among women with long-term or high levels of secondhand smoke exposure [461,466-467].

More research is needed to draw conclusions about a potential link between secondhand smoke and breast cancer risk. 

For a summary of research studies on secondhand smoke exposure and breast cancer, visit the Breast Cancer Research Studies section.

Smoking increases the risk of many cancers, but its effect on breast cancer is still under study.

Although findings on a possible link to breast cancer remain mixed, there’s growing evidence smoking may slightly increase the risk of breast cancer [21,463,466-468].

Some studies show smoking long-term and starting early in life (especially before a first pregnancy) may increase risk later in life [466,468-472]. Other findings show no link between these factors and breast cancer risk [473].

Possible reasons for mixed study findings on smoking

Women who smoke are more likely than non-smokers to be thin, have lower blood estrogen levels and be younger at menopause [474]. All of these factors can lower breast cancer risk [474].

However, other data show smoking may be linked to factors that can increase risk of breast cancer (such as having fewer children and alcohol use) [460].

Certain genes may also affect whether smoking increases breast cancer risk in some people [475-477].

These factors may explain some of the mixed study findings.

Smoking and health

Although smoking may only slightly increase breast cancer risk, stopping smoking, or never starting to smoke, is one of the best things you can do for your health.

Smoking increases the risk of [478]:

  • Heart disease
  • Stroke
  • Bladder cancer
  • Cervical cancer
  • Colon cancer
  • Diabetes
  • Esophageal cancer
  • Kidney cancer
  • Larynx cancer
  • Liver cancer
  • Lung cancer
  • Pancreatic cancer
  • Stomach cancer
  • Throat and mouth cancers 

For a summary of research studies on smoking and breast cancer, visit the Breast Cancer Research Studies section

Smoking and breast cancer survival

For women with breast cancer, the risks from smoking are clearer.

A large pooled analysis of data from about 10,000 women who had been treated for breast cancer found smoking increased the risk of [479]:

  • Breast cancer-specific mortality (death from breast cancer)
  • Overall mortality (death from any cause, not necessarily breast cancer) 

The more women smoked, the higher these risks [479].

Learn more about smoking and breast cancer survival.

For a summary of research studies on smoking and breast cancer survival, visit the Breast Cancer Research Studies section

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Komen Perspectives

Read our perspective on smoking and breast cancer risk.*

*Please note, the information provided within Komen Perspectives articles is only current as of the date of posting. Therefore, some information may be out of date.

Soybeans, as well as other plants like flaxseed, certain grains, beans, fruits and vegetables, contain chemicals called phytoestrogens that mimic estrogen in the body.

Some cell studies have shown soy can increase cancer cell growth [480]. However, many Asian countries (where people eat a lot of soy) have low rates of breast cancer.

This seeming conflict has led to questions about the role of soy in breast cancer risk.

Some studies have found eating a diet high in soy and other phytoestrogens may lower the risk of breast cancer, while others have found no benefit [481-486].

Studies in Asian and Asian-American women tend to show eating a lot of soy lowers breast cancer risk, while studies in non-Asian women show no benefit [482,486].

These findings may differ because Asian women tend to eat more soy throughout their lives (starting early in life) compared to other women [482,486].

Although eating soy doesn’t appear to increase breast cancer risk, whether it lowers risk remains unclear. This topic is under study.

Learn more about estrogen and breast cancer risk.

Learn more about soy and health.  

Learn more about diet and breast cancer.

For a summary of research studies on soy and breast cancer, visit the Breast Cancer Research Studies section.  

 

For a summary of research studies on soy and relief of menopausal symptoms, visit the Breast Cancer Research Studies section.  

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Komen Perspectives

Read our perspective on soy and breast cancer.*

*Please note, the information provided within Komen Perspectives articles is only current as of the date of posting. Therefore, some information may be out of date.

Although one large study found a weak link between life events and breast cancer risk, most studies don’t support a link between stress and breast cancer [487-493].

There doesn’t appear to be a link between stress and breast cancer risk. However, this topic is still under study.

A possible link between vitamin D and breast cancer is under study.

Most of the vitamin D a person gets comes from the sun. A small amount comes from diet.

Vitamin D through sunlight exposure and diet

A few studies have found vitamin D exposure (through diet alone or diet plus sunlight) lowers breast cancer risk [395,494-498].

However, most studies, including 2 randomized controlled trials and a meta-analysis of 11 studies, have found no link between vitamin D (through diet or supplements) and breast cancer risk [495,497,499].

Studying vitamin D presents some challenges. It’s hard to measure sunlight exposure. Also, because so many foods that contain vitamin D also contain calcium, it’s hard to determine the effects of vitamin D alone.

By studying blood levels of vitamin D, researchers can avoid these challenges.

Learn more about diet and breast cancer.

Blood levels of vitamin D

A few studies have found women with higher blood levels of vitamin D had a lower risk of breast cancer compared to women with lower levels [494,500].

Most studies, however, have found no link between blood levels of vitamin D and breast cancer risk [501-504].

More research is needed to learn whether vitamin D affects breast cancer risk.

Learn more about vitamin D.

 For a summary of research studies on vitamin D and breast cancer, visit the Breast Cancer Research Studies section
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Komen Perspectives

Read our perspective on the vitamin D and breast cancer risk.*

*Please note, the information provided within Komen Perspectives articles is only current as of the date of posting. Therefore, some information may be out of date.

Where do the data come from?

Human studies

The data in this section come from 2 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 (such as alcohol use) and an outcome (such as breast cancer) in people.

Although they have the same goal, observational studies and randomized controlled trials differ in:

  • The way they are conducted
  • 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, so it makes it hard to translate findings directly from one to the other.

Animal studies are also designed differently. They often look at exposures in larger doses and for shorter periods of time than are suitable for people.

While animal studies can lay the groundwork for research in people, we need human studies to draw conclusions for people.

All data presented within this section of the website come from studies done with people.

Finding information on risk factors

Susan G. Komen® has up-to-date information on many established, probable and possible risk factors for breast cancer (and information on many factors shown not to increase risk.)

Other organizations conduct research and/or prepare detailed summary reports of research on factors shown to have a link (or no link) to breast and other types of cancer, including:

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, Susan G. Komen® sponsored a study from the National Academies of Sciences, Engineering, and Medicine (formerly the Institute of Medicine), “Breast Cancer and the Environment, a Life Course Approach.”

 

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