Risk factors

Women who are overweight after their menopause have a higher risk of breast cancer than women who are not overweight. Men also have an increased risk of breast cancer if they are overweight or obese. For both men and women, the risk increases as more weight is gained. 

Body mass index (BMI) is a measure that uses your height and weight to work out whether you are a healthy weight. For most adults, an ideal (BMI) is between 18.5 to 24.9. Being overweight means having a BMI of between 25 and 30. Obesity means being very overweight with a BMI of 30 or higher.

Try to keep a healthy weight by being physically active and eating a healthy, balanced diet.

There is a very small increased risk of breast cancer when you take the contraceptive pill. This increase in risk goes back to normal 10 years after you stop taking it.

Remember that breast cancer is rare in young women. Most women who take the pill are in their late teens, twenties and early thirties. So a small increase in this risk during the time women take the pill means very few extra cases of breast cancer.

There is a small increased risk of breast cancer if you’re inactive, this means doing less than 150 minutes of moderate exercise a week. Daily physical activity is recommended to gain health benefits. It can be easier than you think to increase your activity even if you don't do much at the moment. 

Activity doesn’t just mean sport and exercise. Anything that makes you a bit warmer and slightly out of breath counts as moderate activity. 

Most breast cancers occur in women over 50 and it is less common in women under 40.

Ionising radiation includes tests such as x-rays and CT scans and treatment such as radiotherapy.

X-rays and mammograms

Exposure to radiation is known to increase the risk of many types of cancer. Most of us are never exposed to enough radiation to make much difference to our risk.

Nowadays, doctors keep medical exposure to radiation as low as possible. They don't do x-rays or CT scans unless they really need to. And the amount of radiation used is very small.

Many women worry about having mammograms as part of breast screening because it exposes them to x-rays. But the amount of radiation you have with a mammogram is very small.

Radiotherapy

Radiotherapy treatment for breast cancer increases the risk of getting breast cancer in the other breast by a small amount. But this small risk is balanced by the need to treat the original breast cancer.

If you had radiotherapy to your chest area to treat another type of cancer your risk of developing breast cancer is higher than someone who hasn't had radiotherapy. This is especially so for women who have had chest radiotherapy for Hodgkin lymphoma in the past.

If you need radiotherapy for Hodgkin lymphoma or any other type of cancer your doctors should tell you about this risk. They will offer you breast screening if it is appropriate. Talk to your doctor if you are unsure if you should have screening. 

It is important to remember that second cancers are usually found early when they can be successfully treated. Also, radiotherapy treatments are now more focused than in the past.

Breast cancer risk is higher in women with the most dense breast tissue compared to less dense tissue. Women with dense breast tissue have less fat and more breast cells and connective tissue in their breasts.

Our genetic make up affects breast density.

DCIS and LCIS are changes within the breast tissue that might develop into breast cancer in some women. DCIS stands for ductal carcinoma in situ. LCIS stands for lobular carcinoma in situ.

Women with a diagnosis of DCIS or LCIS have double the usual risk of invasive breast cancer in the same or other breast. But it is important to remember that most women with LCIS or DCIS will not develop invasive cancer.

Levels of sex hormones can increase breast cancer risk. These hormones include:

• oestrogen
• progesterone
• testosterone

The male hormone, testosterone, can affect the risk of breast cancer. Women have small amounts of the male hormone testosterone in their bodies.

After the menopause, women with higher levels of oestrogen and testosterone in their blood may have a higher risk of breast cancer.

Women with higher levels of testosterone in their blood before menopause have a higher risk of breast cancer.

There is an increased risk of breast cancer in women with higher levels of a hormone called insulin like growth factor 1 (IGF-1). It is not clear what controls levels of IGF-1 in the bloodstream. It is probably related to our genes, body weight, and how much exercise we do.

Having had breast cancer increases your risk of getting another breast cancer. It might occur in the same breast or in the other breast.

Your specialist will keep a close eye on you with regular check ups. So, a new cancer should be picked up early.  

Having other types of cancer can also increase your risk.

People who had radiotherapy to the chest for Hodgkin lymphoma when they were young have a higher breast cancer risk.

Breast cancer risk is also higher in people who have had any of the following:

• melanoma skin cancer
• lung cancer
• bowel cancer
• womb cancer
• a type of leukaemia called chronic lymphocytic leukaemia

Whether you can have children or when you have them may not be something you can control. Women who have children have a slightly lower risk of breast cancer than women who don't have children. The risk reduces further the more children you have.

Your age when you have your first child also has an effect. The younger you are when you have your first child, the lower your risk.

There has been a lot of research into whether diet increases the risk of breast cancer. So far most findings have been inconclusive and inconsistent.

Research has looked at a number of foods including:

• fat
• dairy foods
• fibre
• fruit
• soya (soy)

Researching diet and breast cancer is very difficult because we all eat such a range of different foods in such differing amounts. A large study called EPIC (the European Prospective Investigation into Cancer) is looking at the links between lifestyle and cancer. It involves around 520,000 people in 10 European countries.

Eating a healthy, balanced diet can help you keep a healthy body weight. There is evidence that being overweight or obese after the menopause, can increase your risk of breast cancer.