Learn The BasicsThe exact cause of breast cancer is not known, as is the case for other types of cancers. However, there are a number of factors that are known to increase the risk of breast cancer.
Biological and demographic risk factors
Biological factors that may increase the risk of developing breast cancer include gender, with women being 100 times more likely than men to develop breast cancer. Other risk factors include age, with those over 55 at a higher risk, ethnicity, with Caucasian women being more likely to be diagnosed with BC than Black women (though there may also be socio-economic reasons for this), having dense breast tissue, a personal medical history of breast cancer and a family history of breast cancer.
Personal medical history
Having had breast cancer in the past is associated with an increased risk of developing the disease a second time, also known as recurrence.
Other non-cancerous diseases affecting the breasts may also increase the risk of developing breast cancer. These include atypical hyperplasia, which is characterized by the buildup of cells in the breast tissue and lobular carcinoma in situ (LCIS), a growth of cells that occurs inside a milk gland.
Starting your period early, i.e., before age 12 and going into menopause late, i.e, after age 55, has also been linked to having an increased risk of developing breast cancer. It is thought that this is because of being exposed to estrogen for longer during the lifetime.
Research has shown that having a first child at an older age, or never having had a child, may also be associated with an increased risk of developing breast cancer.
Family history and genetic changes
A family history of breast cancer, i.e., having an immediate family member with breast cancer, increases the risk of developing it. If the family member was diagnosed before age 50, the risk is further increased.
Mutations in certain genes, like the BRCA1 or BRCA2 genes, have also been associated with an increased risk of breast cancer. However, there are more than 100 different genes, changes in which may be associated with an increased risk of breast cancer.
Environmental risk factors
Environmental risk factors associated with the risk of breast cancer include diet, exercise, exposure to chemicals or radiation, exposure to hormones and exposure to light at night.
Diet
A diet high in saturated fat and low in fresh fruits and vegetables can increase the risk of breast cancer, while eating at least 3.5 to 5 cups of fruits and vegetables each day can help lower the risk.
Being overweight or obese can also increase the risk of developing breast cancer, as can frequently consuming alcohol, with the more alcohol being consumed, the more the risk.
Research has shown that vitamin D may affect breast cancer risk, with those with low vitamin D levels in their blood having a higher risk of breast cancer compared to those with sufficient levels.
Moreover, postmenopausal women who had higher levels of vitamin D in their blood or who reported taking vitamin D supplements at least four times a week had lower rates of breast cancer. However, the current evidence is not sufficient to recommend vitamin D as a preventative measure.
It is important to note that vitamins and supplements should never be taken before consulting with a healthcare professional.
Exercise
A lack of physical activity can increase the risk of developing breast cancer. Research has shown that seven or more hours of physical activity per week is associated with a reduced risk of breast cancer after menopause in women with a family history of the disease.
Pollution and environment
A study called the Sister Study found that women who lived in areas with higher levels of pollution, including lead, mercury, cadmium and nitrogen dioxide (NO2), had a higher risk of developing breast cancer after menopause.
Exposure to airborne radioactive particles has also been shown to be associated with an increased risk of developing a type called estrogen receptor-negative breast cancer.
Smoking, as well as exposure to second-hand cigarette smoke, has also been shown to be associated with a higher risk of breast cancer in younger, pre-menopausal women.
Hair and cosmetic products
The Sister Study also found that women who regularly used hair straighteners and hair dyes were 9% more likely to develop breast cancer than those who did not use these products.
The study also showed that using permanent dyes every five to eight weeks or more was associated with an 8% increase in the risk of developing breast cancer among white women and a 60% increase among Black women.
Exposure to certain chemicals, like triclosan found in cosmetic products and certain chemicals found in sunscreen, may contribute to the development of breast cancer, a study showed. However, the study’s findings were observational and reported only associations with no definitive causation. It remains unclear whether hair and cosmetic products increase the risk of BC.
Exposure to radiation
Research has shown that undergoing radiation therapy to the chest or breasts before age 30 may increase the risk of developing breast cancer later in life.
Exposure to estrogen
Exposure to estrogen has been shown to be associated with an increased risk of developing breast cancer.
This may explain why women are 100 times more likely than men to develop breast cancer. It may also explain why women who had their periods earlier and entered menopause later are at an increased risk of developing breast cancer.
Women can also be exposed to estrogen through other routes. For example, contraceptive pills contains estrogen, and research has shown that certain contraceptive pills can increase the risk of developing breast cancer.
Exposure to diethylstilbestrol (DES), which is a synthetic form of estrogen that was given to pregnant women in the US from 1940 to 1971 to reduce the risk of miscarriage, was associated with an increased risk of breast cancer. This was the case for both women taking DES while pregnant and their children who were exposed to DES while their mother was pregnant.
Disrupted sleep patterns
Long-term disruption of normal sleep–wake cycles, such as working night shifts for many years, has been studied as a possible breast cancer risk factor. This may be related to changes in circadian rhythm and hormone regulation. However, the overall increase in risk appears to be small, and more research is needed to confirm a direct link.
Factors not associated with breast cancer
There are certain myths about factors associated with breast cancer that have no scientific foundations.
These include wearing underwire bras, breast implants, breast injuries, having bigger breasts, deodorants and antiperspirants, undergoing mammograms, consuming caffeine and using plastic dishes, microwaves and cell phones.