Breast cancer risk factors


Breast cancer

Read the answers to your questions about risk factors as part of our Breast Cancer Q&A with experts from Breakthrough Breast Cancer and Breast Cancer Care. For further information about breast cancer, please see the factsheet Pregnancy and Breast Cancer Risk: The Facts

Breastfeeding | Smoking, drinking and diet | HRT and the pill | Stress | Pregnancy | Environmental pollutants | Breast size and risk 

Breastfeeding and breast cancer risk

Letter QHoochie: Are there any research findings on breastfeeding potentially reducing the risk of breast cancer, in mothers and in their breastfed daughters?

Letter QRenaissancewoman: Is there any evidence that breastfeeding helps reduce the incidence of breast cancer? If yes, is there any evidence that longer term breast feeding further reduces incidence of breast feeding eg breastfeeding children to beyond 18 months of age, three times?

Letter ADr Caitlin Palframan, Policy Manager, Breakthrough Breast Cancer: Breastfeeding is an established breast cancer risk factor with a large amount of scientific evidence clearly linking it to a reduction in breast cancer risk.

Research studies show that breastfeeding leads to a slight reduction in a woman's chance of getting breast cancer, if the total length of time she breastfeeds is five months or more. This five-month period can be for one child or more than one child. So for example, breastfeeding one child for three months and a second child for two months would give the same degree of protection against breast cancer as breastfeeding one child for five months.

The longer the length of time a woman breastfeeds overall, the greater the reduction in her risk of breast cancer. The reduction in breast cancer risk by breastfeeding is relatively small. The benefit or protection due to breastfeeding for about five months is to prevent about two out of 1,000 women from developing breast cancer.

There are many important benefits from breastfeeding for both mother and child. The Department of Health recommends that women breastfeed exclusively for the first six months of an infant's life as it provides all the nutrients a baby needs as well as antibodies to help fight illness and infection. Breakthrough thinks that a woman should decide for herself whether to breastfeed her baby. Her decision should take into account the benefits for both her and her child and the practical issues associated with breastfeeding.

Smoking, drinking and diet in breast cancer risk

Letter QDinahrod: I do not smoke or drink and I breastfeed my children, but diet could be better - how significant are these factors?

Letter QMaryAnnSinglton: I guess that my having had my son later in life (at 38) and not being able to breastfeed him might have contributed to my breast cancer, as I don't smoke, my weight is fine, I don't drink too much and have reasonably healthy diet.

Letter A

Dr Caitlin Palframan: Lots of studies have looked at smoking and breast cancer. There is currently no reliable scientific evidence that smoking has an effect on the risk of breast cancer. Irrespective of any potential breast cancer risk, smoking is a major cause of lung and other cancers as well as heart disease and all women and men are strongly advised not to smoke by the Department of Health, health professionals and health charities.

Alcohol is an established breast cancer risk factor with a large amount of scientific evidence clearly linking it to an increased breast cancer risk. The more you regularly drink, the higher your chance of getting breast cancer at some point in your life. Women who usually drink only a little alcohol on a regular basis may have only a very small increased risk of breast cancer compared to women who don't drink at all. Current evidence suggests that all types of alcohol, including wine, beer and spirits, are associated with an increased risk of breast cancer.

Unlike many other established breast cancer risk factors, alcohol consumption is something we can change. The important message is to be aware of how many units of alcohol you are drinking and to drink in moderation. The Department of Health recommends that women drink no more than 2-3 units of alcohol per day.

Finally, over the past 20 years there has been a great deal of research into the link between diet and breast cancer. We know that being overweight after the menopause or gaining weight in adulthood can increase breast cancer risk, but we still aren't sure which specific dietary factors influence the chance of developing the disease.

Even though more scientific research is needed before we can be sure about the links between diet and breast cancer, we are all encouraged to follow a healthy lifestyle by:

  • Eating a healthy balanced diet that is rich in fruit, vegetables and whole grain foods and is limited in red meat, animal fat and sugary or fatty foods
  • Limiting alcohol consumption
  • Exercising regularly
  • Maintaining a healthy weight

Following a healthy lifestyle will help to maintain general good health, a healthy body weight and reduce the risk of many diseases, including heart disease, diabetes, and other cancers. 

There are lots of different factors that can influence a woman's risk of developing breast cancer. However, it's important to remember that risk factors don't necessarily cause breast cancer. Even when someone has been diagnosed with breast cancer, we can't say if it is down to a particular risk factor.

HRT and the Pill

Letter Q10poundstogo: Is it true that I should steer clear of HRT when the time comes? I was on the Pill for years before having my children. Will this increase the risk to me in the context of my family history?

Letter Qnotobvious: I'm on HRT and it has transformed my life, I'm happier, livelier, have my libido back and my skin is great. It is easy enough to find the figures for the percentage increase in risk after being on HRT for a certain number of years. What I want to do is to do a balancing exercise to work out how much risk I'm saving by not drinking or being overweight and balancing that against the increased risk of the HRT - does anyone know where I can find the figures?

Letter ADr Farah Rehman, Avon Clinical Fellow, Breakthrough Breast Cancer Research Centre: Studies have shown that the use of combined HRT and oestrogen-only HRT can increase the risk of breast cancer and this risk increases the longer they are used. The risk associated with taking oestrogen-only HRT is less than that with combined HRT. The good news is that the increased risk of breast cancer begins to fall as soon as HRT is stopped. Within five years of stopping HRT, a woman's chance of developing breast cancer is about the same as if she had never taken HRT.

Women who are taking the combined contraceptive pill have a slightly higher risk of breast cancer compared with those who are not. Ten years after stopping the Pill, this increased risk disappears and the chance of developing breast cancer becomes about the same as that of a woman who has never taken the Pill. In general, however, breast cancer is rare among women under the age of 40, whether or not they take the contraceptive pill.

For further information about the pill and breast cancer see our factsheet The Pill and Breast Cancer Risk: The Facts which is available online at

Breast cancer is thought to be caused by a combination of our genes, lifestyle and environment, however very little is known about the exact causes. As there are many interacting factors in every woman's life, it is difficult to say what the exact risk is for each individual woman regarding their various risk factors.

This is why Breakthrough is supporting the Breakthrough Generations Study, which will investigate the causes of breast cancer and aims to gain information on causes that might be preventable. Launched in 2004, this is the largest and most comprehensive study of its kind, including over 100,000 women from across the UK. The study will continue to give information for the next 40 or 50 years. It is likely that a combination of factors contribute to breast cancer. By examining the effects of genetic, environmental, behavioural and hormonal factors, we hope that the study will pinpoint the causes of breast cancer and how we can prevent this disease in the future.

Stress and breast cancer risk

Letter Qstrandedatsea: Is there a link between emotional stress and breast cancer, or any cancer?

Letter ADr Caitlin Palframan: A few studies have looked at the link between emotional stress and breast cancer. There is no clear evidence that stress can, directly or indirectly, increase the risk of the disease. Stress is a highly subjective state so it is difficult to measure – how one person determines their stress levels or reacts to stress can be very different from how another person does. This makes the effects of stress on breast cancer risk difficult to untangle from other lifestyle risk factors.

Pregnancy and breast cancer risk

Letter QSmee: Until I was diagnosed with breast cancer, I thought that having a child would have helped to decrease my risk. However, apparently anyone who has a child over 35 is now deemed to be at higher risk - I was 37. Shouldn't we start some sort of campaign to raise awareness of this? So many of us are choosing to have children later in life and even if it only gives them a slightly increased risk, surely they should be aware of it.

Letter ADr Caitlin Palframan: Reproduction has a complex effect on breast cancer risk, but in general pregnancy is believed to have three effects on the risk of developing the disease.

First, the age at which you have children affects risk. Women who have their first pregnancy at an earlier age have a lower risk than women who begin their family at later ages. For example, having a baby at the age of 20 rather than at the age of 30, on average prevents three out of 100 women developing breast cancer later on in life.

Second, the long-term risk of breast cancer also slightly decreases the more children you have. Women who have not had children are at higher risk of breast cancer than women who have had children.

The third effect is different however. In the short term, research studies suggest that, irrespective of your age, after you give birth your risk of breast cancer slightly increases. We don't know the reasons for this but it is thought to be due to hormone changes. This increase in risk is temporary, lasting a few years, and it is important to remember that breast cancer during childbearing years is rare.

There are many factors that will influence a woman's decision whether and when to have children, as well as how many children she has. Breakthrough believes it is important that women do not base their decisions solely on the fact that having a child at a younger age may reduce the chances of developing breast cancer later on in life. There are many other important factors for women to take into account in order to make the decisions that are right for them.

Environmental pollutants and breast cancer risk

Letter QSakura: How seriously does the government take the link between environmental pollutants and carcinogens, and breast cancer? 

Letter ADr Caitlin Palframan: There has been some concern that environmental factors may have a role in increasing breast cancer risk. Some chemicals, such as pesticides, have a similar structure to oestrogen: this has led to speculation that these chemicals can increase the risk of breast cancer. It is thought to take many years for most breast cancers to develop and it is very difficult to work out what chemicals women with breast cancer have been exposed to over 10, 20 or even 30 years before their breast cancer is detected.

It is also hard to isolate the effects of individual chemicals on breast cancer risk when we are exposed to low levels of thousands of chemicals during our lifetime. 

Lots of studies have looked at the link between chemicals in our environment and breast cancer. Overall, there is currently no good evidence that normal exposure to environmental chemicals increases the risk of breast cancer. Breast cancer is likely to be caused by many factors, and we don't know how the combination of an individual's lifestyle, environment and genes contribute to breast cancer development. It may not be possible to unravel the effects of any one particular chemical from the rest of these factors or other chemicals we may be exposed to.

Letter Qcupcaked: I'm concerned about oestrogen-like hormones given to cattle, which was not done on such a widespread basis until about 40 years ago. Are we now getting more oestrogens through our diet? Is this also why breast cancer is not as common in Asian/Chinese women, where the diet uses less dairy?

Letter QRenaissancewoman: Is there any evidence of a link between diet rich in animal fat/dairy foods being causative in breast cancer? Conversely is there any evidence of vegetarians having lower rates of breast cancer?

Letter ADr Caitlin Palframan: Oestrogen-like hormones are not given to cattle in the UK. The link between dairy products and breast cancer risk has been investigated in a large number of studies, but it is not clear if eating dairy products has any effect on a woman's risk of breast cancer.

Some studies have looked at specific dairy products, such as milk or cheese, whereas others have looked at dairy products in general. Several large studies have found that eating dairy products did not affect a woman's risk of developing the disease. Other studies have suggested that dairy products, particularly low-fat products, might decrease the risk of breast cancer, while a few studies have suggested that dairy products, in particular high fat products, might increase the risk of the disease.

At the moment there is no good scientific evidence to recommend that women alter their consumption of dairy products in order to reduce their risk of breast cancer. The decision to include or exclude dairy products in your diet should be based on nutritional requirements and personal choice. If you do eat dairy products, you should choose low-fat versions for a healthy, balanced diet. If you choose not to eat dairy products you should ensure that you include alternative sources of calcium in your diet, such as bony fish (like pilchards and sardines), leafy green vegetables (for example broccoli, cabbage, pak choi, but not spinach) and sesame seeds.

Studies looking into the link between meat and poultry and breast cancer are inconsistent and more research is needed before we can be sure whether or not there is a link


Letter QSakura: Plastic mimics oestrogen as well. Hard plastic is now banned in Canada for children's toys and baby bottles. Research shows more baby girls are being born than ever before and it could be connected to the enormous oestrogen levels in the mother.

Letter ADr Caitlin Palframan: There has been some concern that chemicals in the environment, such as those used to make plastic, may have a role in increasing breast cancer risk. Bisphenol A is used in the manufacture of polycarbonates, epoxy resins and PVC plastics. Polycarbonates are found in plastic bottles, infant feeding bottles, plastic tableware and food storage containers. Epoxy resins are used in the linings of food and beverage cans as well as vats for wine-making. As a result of this, small amounts of bisphenol A can transfer into foods. There are strict regulations for the manufacture of food storage materials to limit this transfer. The amount of transfer that is permitted by the EU is well below the limit at which Bisphenol A is considered to be harmful to humans.

Studies have suggested that bisphenol A may be a type of chemical known as an endocrine disruptor. These are synthetic chemicals that, when absorbed into the body, either mimic or block natural sex hormones (such as the female hormone oestrogen) and disrupt the body's normal functions. However, it is important to remember that the hormonal activity of these chemicals is many times weaker than the body's own natural hormones.

There is currently little information on the effects of exposure to low doses of bisphenol A before or after birth on breast cancer risk. There have been some studies investigating the effects of exposing mice and rats to bisphenol A just before birth or in adulthood. The results of these studies have indicated that exposure to bisphenol A in adulthood did not increase the risk of breast cancers developing, but more studies are needed to determine the effects of bisphenol A exposure before birth on breast cancer risk. As the research available has only been carried out in animals, more research is needed to determine if the effects of bisphenol A exposure would be the same in humans.

There is currently no evidence to suggest that bisphenol A can increase the risk of breast cancer. However, more studies are required in order to determine whether low levels of bisphenol A (comparable to the level a woman would be exposed to under normal circumstances) have any effect on the risk of breast cancer in humans and whether women are more vulnerable to the effects of this chemical at different life stages such as before birth, during puberty or during pregnancy.

Breast size and breast cancer risk

Letter QRenaissancewoman: Is there any evidence that larger-breasted women are more prone to breast cancer?

Letter ADr Caitlin Palframan: There is no good evidence that shows a correlation between the size of a woman's breasts and her breast cancer risk.

We have made every effort to ensure that the content of these answers is accurate and up to date, but we accept no liability in relation to typographical errors or third-party information. Please be aware that the responses from the Breast Cancer Care and Breakthrough Breast Cancer teams are not a substitute for professional medical care. If you have any concerns about your breast health or any treatment you are receiving you should discuss these with your doctor. Responses from Breast Cancer Care and Breakthrough Breast Cancer are only accurate at the time of posting as medical knowledge and treatment can change over time.

Last updated: over 1 year ago