A risk factor is anything that increases your chances of getting a disease, such as breast cancer. But having a risk factor, or even many, does not mean that you are sure to get the disease.
Certain breast cancer risk factors are related to personal behaviors, such as diet and exercise. Other lifestyle-related risk factors include decisions about having children and taking medicines that contain hormones.
Drinking alcohol
Drinking alcohol is clearly linked to an increased risk of breast cancer. The risk increases with the amount of alcohol consumed. Women who have 1 alcoholic drink a day have a small (about 7% to 10%) increase in risk compared with non-drinkers, while women who have 2 to 3 drinks a day have about a 20% higher risk than non-drinkers. Alcohol is linked to an increased risk of other types of cancer, too.
It is best not to drink alcohol. For women who do drink, they should have no more than 1 drink a day.
Being overweight or obese
Being overweight or obese after menopause increases breast cancer risk. Before menopause your ovaries make most of your estrogen, and fat tissue makes only a small part of the total amount. After menopause (when the ovaries stop making estrogen), most of a woman’s estrogen comes from fat tissue. Having more fat tissue after menopause can raise estrogen levels and increase your chance of getting breast cancer. Also, women who are overweight tend to have higher blood insulin levels. Higher insulin levels have been linked to some cancers, including breast cancer.
Still, the link between weight and breast cancer risk is complex.
For instance, the risk of breast cancer after menopause is higher for women who gained weight as an adult, but the risk before menopause is actually lower in women who are obese. The reasons for this aren’t exactly clear.
Weight might also have different effects on different types of breast cancer. For example, being overweight after menopause is more strongly linked with an increased risk of hormone receptor-positive breast cancer, whereas some research suggests that being overweight before menopause might increase your risk of the less common triple-negative breast cancer.
The American Cancer Society recommends you stay at a healthy weight throughout your life and avoid excess weight gain by balancing your food intake with physical activity.
Not being physically active
Evidence is growing that regular physical activity reduces breast cancer risk, especially in women past menopause. The main question is how much activity is needed. Some studies have found that even as little as a couple of hours a week might be helpful, although more seems to be better.
Exactly how physical activity might reduce breast cancer risk isn’t clear, but it may be due to its effects on body weight, inflammation, hormones, and energy balance.
The American Cancer Society recommends that adults get 150 to 300 minutes of moderate intensity or 75 to 150 minutes of vigorous intensity activity each week (or a combination of these). Getting to or going over the upper limit of 300 minutes is ideal.
Not having children
Women who have not had children or who had their first child after age 30 have a slightly higher breast cancer risk overall. Having many pregnancies and becoming pregnant at an early age reduces breast cancer risk.
Still, the effect of pregnancy on breast cancer risk is complex. For example, the risk of breast cancer is higher for about the first decade after having a child, particularly for hormone receptor-negative breast cancer (including the less common triple-negative breast cancer). The risk then becomes lower over time.
Not breastfeeding
Most studies suggest that breastfeeding may slightly lower breast cancer risk, especially if it’s continued for a year or more. But this has been hard to study, especially in countries like the United States, where breastfeeding for this long is uncommon.
The explanation for this possible effect may be that breastfeeding reduces a woman’s total number of lifetime menstrual cycles (the same as starting menstrual periods at a later age or going through early menopause).
Birth control
Some birth control methods use hormones, which might increase breast cancer risk.
Oral contraceptives: Most studies have found that women using oral contraceptives (birth control pills) have a slightly higher risk of breast cancer than women who have never used them. Once the pills are stopped, this risk seems to go back to normal within about 10 years.
Birth control shot: Depo-Provera is an injectable form of progesterone that’s given once every 3 months for birth control. Some studies have found that women currently using birth-control shots seem to have an increase in breast cancer risk, but other studies have not found an increased risk.
Birth control implants, intrauterine devices (IUDs), skin patches, vaginal rings: These forms of birth control also use hormones, which in theory could fuel breast cancer growth. Some studies have shown a link between use of hormone-releasing IUDs and breast cancer risk, but few studies have looked at the use of birth control implants, patches, and rings and breast cancer risk.
Hormone therapy after menopause
Hormone therapy with estrogen (often combined with progesterone) has been used for many years to help relieve symptoms of menopause and help prevent osteoporosis (thinning of the bones). This treatment goes by many names, such as post-menopausal hormone therapy (PHT), hormone replacement therapy (HRT), and menopausal hormone therapy (MHT).
There are 2 main types of hormone therapy. For women who still have a uterus (womb), doctors generally prescribe estrogen and progesterone (known as combined hormone therapy, or just HT). Progesterone is needed because estrogen alone can increase the risk of cancer of the uterus. For women who’ve had a hysterectomy (who no longer have a uterus), estrogen alone can be used. This is known as estrogen replacement therapy (ERT) or just estrogen therapy (ET).
Combined hormone therapy (HT): Use of combined hormone therapy after menopause increases the risk of breast cancer. This increase in risk is typically seen after about 4 years of use. Combined HT also increases the likelihood that the cancer may be found at a more advanced stage.
The increased risk from combined HT appears to apply mainly to current and recent users. A woman’s breast cancer risk seems to go back down within 5 years of stopping treatment.
Bioidentical hormone therapy: The word bioidentical is sometimes used to describe versions of estrogen and progesterone with the same chemical structure as those found naturally in people (as opposed to the slightly different versions found in most medicines). The use of these hormones has been marketed as a safe way to treat the symptoms of menopause. But because there aren’t many studies comparing “bioidentical” or “natural” hormones to synthetic versions of hormones, there’s no proof that they’re safer or more effective. More studies are needed to know for sure. Until then, the use of these bioidentical hormones should be considered to have the same health risks as any other type of hormone therapy.
Estrogen therapy (ET): Studies of the use of estrogen alone after menopause have had mixed results, with some finding a slightly higher risk and some finding no increase. If ET does increase the risk of breast cancer, it is not by much.
At this time there aren’t many strong reasons to use post-menopausal hormone therapy (either combined HT or ET), other than possibly for the short-term relief of menopausal symptoms. Along with the increased risk of breast cancer, combined HT also appears to increase the risk of heart disease, blood clots, and strokes. It does lower the risk of colorectal cancer and osteoporosis, but this must be weighed against the possible harms, especially since there are other ways to prevent and treat osteoporosis, and screening can sometimes prevent colon cancer. ET does not seem to increase breast cancer risk, but it does increase the risk of stroke.
The decision to use HT should be made by a woman and her doctor after weighing the possible risks and benefits (including the severity of her menopausal symptoms), and considering her other risk factors for heart disease, breast cancer, and osteoporosis. If they decide she should try HT for symptoms of menopause, it’s usually best to use it at the lowest dose that works for her and for as short a time as possible.
To learn more, see Menopausal Hormone Therapy and Cancer Risk.
Breast implants
Breast implants have not been linked with an increased risk of the most common types of breast cancer. However, they have been linked to a rare type of non-Hodgkin lymphoma called breast implant-associated anaplastic large cell lymphoma (BIA-ALCL), which can form in the scar tissue around the implant. This lymphoma appears to happen more often in implants with textured (rough) surfaces rather than smooth surfaces. If BIA-ALCL does occur after an implant, it can show up as a lump, a collection of fluid, swelling, or pain near the implant, or as a change in a breast’s size or shape.