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Lifestyle-Related Causes

Besides these genetic or biological risk factors, certain behaviours or lifestyle choices may increase the risk of developing breast cancer. Since it is possible to change these habits, these risk factors are considered modifiable.

Lowering the risk thus requires making changes to one’s lifestyle. However in some cases it might be difficult to give up some of these practices to lower the risk of breast cancer. For instance, hormonotherapy could be beneficial to a woman dealing with the acute symptoms of menopause. It is best to discuss your risk factors with a doctor to make the best possible decision for your health.

Exposure to Ionizing Radiation at a Young Age
Having received radiation or ionizing radiation to treat a medical condition is a risk factor for breast cancer. The risk is higher if the treatment was administered with chemotherapy at puberty or before the age of 15.

Increased Exposure to Hormones
Women may choose to take oral contraceptives for reasons related to either lifestyle or health. Similarly, women may opt to follow a course of prolonged hormone replacement therapy (HRT) to relieve the acute symptoms of menopause. It should be noted, however, that in both instances this increases the level of female hormones associated with the risk of breast cancer.

Oral Contraceptives Like “the Pill”
Oral contraceptives often contain estrogen and progesterone, two hormones that are likely to increase the risk of developing breast cancer, especially in women who have used these contraceptives for 10 years or more. However, the increased risk disappears once the woman stops using oral contraceptives. Women who are now using or have used oral contraceptives for less than 10 years are at a slightly higher risk for breast cancer than women who haven’t.

If you choose to take the Pill as a method of contraception, it is important that you do the following:

  • observe your breasts on a regular basis;
  • undergo a clinical breast examination.

Perimenopausal Hormonotherapy
Doctors may prescribe a treatment called hormone replacement therapy (HRT) to relieve the severe symptoms of menopause. This treatment is sometimes also combined with another hormone: progestin, a synthetic form of progesterone.

While in general HRT relieves women of the unpleasant symptoms of menopause, it does, however, increase the risk of breast cancer, as it is based on estrogen, a hormone linked to the disease. Studies have shown that the risk of developing breast cancer increases after having taken HRT for five years or more, and is even greater if this therapy also includes progestin.

The increased risk seems to disappear a few years after the end of the treatment. However, many researchers believe that the risks associated with long-term HRT combined with progestin outweigh the benefits of this treatment.

Women experiencing severe symptoms of menopause must therefore, with their doctor’s assistance, make the best decision for their health: whether or not to take HRT while considering both the unpleasant symptoms of menopause and the personal risk factors for developing breast cancer.

Regardless of what decision is made, it is strongly recommended that pre- and post-menopausal women conduct regular breast observation to detect all lumps or abnormal changes. It is important to remember that the risk of developing breast cancer increases with age. Furthermore, we strongly recommend that women between 50 and 69 years of age have a mammography every two years.

First Pregnancy at a Later Age or No Pregnancy Carried to Full Term
During pregnancy, women’s breast cells are temporarily blocked from exposure to the circulating estrogen. Consequently, the more pregnancies a woman has, the less she is exposed to this hormone linked to breast cancer, as opposed to women who have not had any children or who have not carried any pregnancy to term.

Moreover, women who had their first pregnancy after the age of 30 are at a slightly higher risk than women who had a full-term pregnancy at a younger age.

Finally, many studies show that breastfeeding is considered to be a protective factor against breast cancer.

High-Density Breast Tissue
Breasts are considered dense if they are made up of a greater amount of connective tissue (between the glands and ducts), and of glands and lactiferous ducts, than of fatty tissue (adipose). Only a mammography can determine the density of the breast. The mammography allows us to see the contrasts between radio-opaque dense tissue (seen in white) and radio-translucent fatty tissue (seen in gray).

Here is an example of a low-density and a high-density breast:

Women with dense breasts are at a greater risk of developing breast cancer than other women. Breast density decreases with age and after menopause. Nonetheless, breast density is considered a modifiable risk factor since it can be influenced by our lifestyle choices. For example, hormone replacement therapy, a first pregnancy at a later age or absence of pregnancy and the consumption of alcohol are all associated with increased breast density. On the other hand, taking vitamin D could decrease breast density and therefore reduce the risk of developing breast cancer.

Smoking and Exposure to Second-Hand Smoke
Current knowledge acquired through scientific research indicates that smoking or being exposed to second-hand smoke can increase the risk of developing breast cancer. Thus, recent studies show that: 

  • smoking could increase the risk of breast cancer in premenopausal and postmenopausal women;

  • a link could exist between exposure to second-hand smoke and breast cancer, especially in young premenopausal women who have never smoked.

More studies are needed, however, to determine the actual effect of active smoking and of exposure to second-hand smoke on the number of breast cancer cases and on the mortality rate for this disease.

That being said, smoking and being exposed to cigarette smoke are harmful to your general health. The Quebec Breast Cancer Foundation encourages you therefore to quit smoking if you are a smoker, and to avoid second-hand smoke.

Consumption of Alcohol
Drinking alcohol, even in small quantities, increases the risk of breast cancer. Moreover, this risk increases proportionately with the amount consumed. There are two reasons for this: 

  • alcohol could boost the level of estrogen, a hormone linked to breast cancer;

  • alcohol could also reduce the presence of essential nutrients such as folic acid, a type of vitamin B, and vitamins A and C that protect against cell damage.

We recommend that you limit your consumption of alcohol to one glass a day for five days a week maximum.

Excess Weight Gain After Menopause
Obesity increases the risk of developing breast cancer in postmenopausal women. After menopause, fatty tissue produces a small quantity of estrogen. An increased level of this hormone is linked to breast cancer.

Sedentary Lifestyle (Being Physically Inactive)
Research indicates that the absence of physical activity is a risk factor for breast cancer. Conversely, these studies also reveal a link between regular physical activity and a reduced risk of developing the disease in premenopausal and postmenopausal women. Walk, run, move… It’s never too little to derive benefits from it.

Other Risk Factors

Recent studies reveal other possible risk factors.

  • Weight Gain During Adulthood
    Weight gain during adulthood can increase the risk of developing breast cancer during menopause. However, studies are needed to determine if weight loss can reduce this risk.
  • Deficiency of Vitamin D
    Recent studies suggest that women with a low intake of vitamin D are at a higher risk of developing breast cancer. Vitamin D is a nutrient found mainly in fatty fish and eggs, as well as dairy products. Vitamin D is also produced by the skin when it’s exposed to the sun. However, we know that sun exposure increases the risk of skin cancer. Besides the known benefits of vitamin D on bone health, several studies are currently underway to show the benefits of this vitamin on breast health.