As awareness of breast cancer increases, interest is growing around ways to prevent it. Breast cancer survivors are especially likely to make risk reduction a priority. Yet there is so much misunderstanding about “risk” which in public health is not merely an emotive word, but a statistical concept with a precise meaning.

Some known risks cannot easily be controlled – such as your genes, the age at which you begin menstrual cycles, and the age at which you reach menopause. It is believed that inherited risk accounts for around 10% of all breast cancers. Other known risk factors such as the timing of pregnancy, birth and breastfeeding, often involve choice but – realistically – are not likely to shift in respect of what amounts to a relatively small improvement in lifetime breast cancer risk.

On the other hand, information claiming to be authoritative about cancer prevention is often promoted to the public, despite offering little solid scientific support for interventions that may not only be inconvenient but also – often – quite costly.

There is a clear need for researchers to sort through the facts, the myths and the concerns, for everyone’s sake. Research of this nature is difficult and expensive; large samples of women must be followed for long periods of time, after giving accurate, detailed accounts of health behaviours or environmental exposures. Nonetheless, the research is being done and the results are being made available. In 2011, the Institute of Medicine in the USA reviewed the evidence base for environmental risk factors associated with breast cancer. The entire report can be downloaded here.

Six risk factors

The following six risk factors emerged with strong research support from this review.

1. Ionising radiation. This radiation is involved in X-rays and CT scans. Ionising radiation separates electrons from their atoms, creating an intra-cellular electrical charge which is capable of breaking DNA, the machinery of cellular reproduction. Cells damaged in this way will mostly die or be repaired by the body’s own defence mechanisms, but some may continue to reproduce forming a cancer growth. Until recently, it was assumed that normal X-rays were not a significant source of radiation exposure, but researchers have found that the “dose effect” is to some extent cumulative. So a few X-rays done when really necessary are not of concern, but repeated X-ray imaging should be avoided. CT scans (Computerised Tomography) which build up a picture using multiple X-rays involve large doses of ionising radiation and are definitely cause for concern, especially in children – though despite the increased cancer risk the use of a CT scan may still be safer than alternatives such as exploratory surgery.

The US Food and Drug Administration provides detailed information here on the risks and benefits of X-ray imagery. A further issue – especially in the public sector of a developing country like South Africa – is that X-ray operators need to maintain high technical standards and skill levels, in order to avoid accidentally exposing patients to excess doses of radiation.

What about mammography? This should be discussed with your doctor. Regular mammography is not recommended for younger patients except those at particular risk because of inheritance; but for women over 40, the benefits of early cancer detection outweigh the slight increase in risk from X-ray exposure. The same can be said of therapeutic radiation (‘radiotherapy’) which may be used to kill cancer cells, whilst making every effort to protect healthy tissues from the radiation.

Studies have not found that non-ionising radiation, e.g. the energy produced by microwave ovens and cell phones amongst other everyday gadgets, has anything to do with cancer. Similarly, MRI and Ultrasound scans, which create internal images using different technologies, are safe.

2. Limiting alcohol consumption. Even moderate drinking – one alcoholic drink per day – produces a slightly higher risk that a woman will develop breast cancer. Yet drinking the same amount helps to fight heart disease and strokes! What’s a woman to do? If, in discussion with your doctor, you realise that your personal cancer risk is elevated, it makes sense to avoid alcohol, taking care of your heart in other ways. And meanwhile, consumption beyond this moderate level is harmful to the body, so if you regularly drink more than one daily unit, the guideline is clear: cut down.

3.Hormone Replacement Therapies that include both oestrogen and progestin have been shown to increase the risk of breast cancer, and should be avoided unless medically indicated. However, if your life is badly affected by the hormonal shifts of menopause, the benefits to your overall health and well being may be worth a (temporary) increase in breast cancer risk, so discuss the options with your doctor. If you’re worried about HRT which is now discontinued, things may not be so bad: up to five years after stopping some risk remains. but after that you would have the same risk as someone who never used HRT. Similar reasoning applies to combined oral contraceptives, which also affect hormonal pathways and carry a slightly increased risk of breast cancer during active use and for a short time thereafter – though in this case, patients are usually younger with a lower ‘background risk’ of breast cancer which fades to insignificance beside the risk of an unwanted pregnancy. Older women, however, may want to plan for safer contraceptive options.

4. Smoking. Smoking causes a slight increase in breast cancer risk, especially if you started when very young or before your first pregnancy. It’s not a huge factor in breast cancer – though it is a factor – and unfortunately, based on current knowledge, the breast cancer risk may not reduce if you stop. Still, that is hardly relevant considering the dreadful health effects of smoking – which not only causes lung cancer but increases your risk for cancer to occur in the mouth, lips, nose and sinuses, voice box, throat, oesophagus, stomach, pancreas, kidney, bladder, uterus, cervix, colon/rectum, ovary, and blood (myeloid leukaemia). If a breast cancer scare motivates you to finally stop smothering these tissues in carcinogens and toxins, your entire body will be grateful.

5. High Body Mass Index (BMI)  Carrying excess weight adds significantly to your risk of breast cancer – especially after menopause, and especially if you gained the extra weight (as most people do) after the age of 18. Dr Ruth Travis, a UK based cancer researcher, says:

At present the only clear oestrogen-related risk factor for breast cancer that is amenable to change is obesity after the menopause. Thus, prudent advice is to maintain weight such that body mass index is below 25 kg/m2 (

Obesity is “oestrogen related” because after menopause, oestrogen is stored along with body fat. Prior to menopause, this makes little difference and may even help to limit circulating oestrogens, but once the monthly cycles cease, oestrogen stored along with body fat becomes a significant risk factor. Studies of patients who have undergone bariatric surgery, as well as the Nurses’ Health Study in the USA have shown that sustained weight loss reduces breast cancer risk by at least 40%, which is a significant improvement.

6. Exercise. More regular physical exercise will not only help you to lose weight sustainably, but in itself reduces breast cancer risk. Trials of previously sedentary post-menopausal women found that three hours of moderate exercise per week achieved positive changes in weight, BMI, abdominal fat, hormone concentrations and insulin – which adds up to better health all round. Whilst it’s not clear that exercise makes much difference to the risk levels of pre-menopausal women, it’s easier to keep up a lifestyle that is active from a young age.

What’s more, exercise has health benefits at every season of life – and it doesn’t require hours of boredom at the gym either. Cutting-edge research in the UK has shown that as long as you don’t sit for hours at a time, just a few minutes of vigorous exercise per week can produce significant health benefits! This method, called High Intensity Training or HIT, could change the way we look at exercise and health – but please bear in mind that if you aren’t used to it, you should not try high intensity exercise even in short bursts without checking with your doctor first. More on HIT is here.

More research needed

There are several areas where more research is needed to understand how the constantly changing breast tissue interacts with different environmental risk factors. Firstly, we need to know more about early exposure – in infancy, childhood and around puberty. Secondly, there are a few other suspected factors which could increase risk, but research so far is inconclusive. Shift work that disrupts natural circadian rhythms, chemicals that mimic oestrogen (including those that leach from plastics), phyto-oestrogens from e.g. unfermented soy products, mutagens or chemicals known to produce genetic changes (such as polycyclic aromatic hydrocarbons found in heavy oil, exhaust fumes, coal tar and charred food), and chemicals that affect the expression of genes (including BPA and some byproducts of alcohol metabolism) – all these are potential risks but need more research. There isn’t enough evidence at this stage to say for sure that these things promote breast cancer, but it may still be sensible to avoid exposure wherever practicable, and in particular to avoid exposing children and teenagers to these potential risks.


In summary, breast cancer is a complex disease affecting a very complex body tissue and evolving not just over a decade or two of later life when most cases are diagnosed, but throughout the life course. Whilst there is still much that is not understood about the different types of tumour that can occur, the research done so far is making a difference and giving us tools for prevention.

Since prevention is always better than cure, the more we know about how to reduce our own risks for breast cancer, and that of our daughters, the better for women’s health both now and into the future.