The world's authority on environmental causes of cancer argues that breast cancer can largely be prevented by minimising a variety of dietary, environmental and lifestyle risks.
Breast cancer is frightening
because it appears to be so random and unavoidable. At the same time that we hear how many more women are being diagnosed with breast cancer every year now more than 186,000 in the US and 33,000 in the UK news reports and magazine articles tell us how little science knows about what causes cancer and how to prevent it. Not a day goes by, it seems, without the announcement of a new avenue of genetic research or developments in diagnostic or treatment strategies. But only a very small percentage of all breast cancer cases have a direct genetic cause.
The most important story the story that could truly save lives is not being told. Contrary to popular belief, you do have significant control over your risks of breast and other types of cancers.
Cancer does not strike randomly, but requires certain conditions, exposure to toxic substances, or both, to occur. Just as most cases of heart disease are triggered by a combination of high fat foods and a lack of physical activity, most cases of breast cancer can be traced to one or a combination of risks (see box below).
The role of oestrogen
The evidence is overwhelming that oestrogen is intimately connected to the development of most breast cancer. Under oestrogen's influence, cells multiply and swell in preparation for possible milk production. Oestrogen encourages breast cells to divide more often and more rapidly. Thus if a mutation (inherited or triggered by a carcinogen) lies embedded in the DNA, cancer cells are more likely to proliferate when oestrogen levels are high.
We now know that two distinct types of breast cancer exist: the far more common oestrogen dependent breast cancer, influenced primarily by oestrogen, and the less common non oestrogen dependent breast cancer. More than two thirds of women with breast cancer have oestrogen dependent cancers, and that number is increasing at a particularly alarming rate. According to a 1990 study, the incidence of oestrogen dependent breast cancers, particularly among postmenopausal women, increased by 130 per cent from the mid 1970s to the mid 1980s, in contrast to only a 27 per cent increase in non oestrogen dependent cancers (J Nat Cancer Inst, 1990; 82: 693-6).
Why is oestrogen dependent breast cancer so much more common today than it was just a few decades ago? Plainly speaking, the average woman is exposed to more oestrogen over a longer period of time than ever before and at the same time, she is exposed to more carcinogenic, or "bad" oestrogen, than women were in the past.
According to one major study, the risk associated with having an early menarche for instance, one that takes place at the age of 10 is approximately twice that associated with a menarche that occurs much later, say at the age of 16 or so (Nature, 1989; 338: 389-94).
The same kind of risk profile exists at the other end of the fertility cycle: the younger a woman is at menopause, the lower her risk of breast cancer.
The good news is that you do have some control over the length of time your body naturally produces oestrogen: a recent study of some 200 women between 17 and 22 found that those whose diets were high in fibre and low in animal fat had a later menarche and subsequently fewer ovulatory and menstrual cycles than did those whose diet included more high fat, low fibre foods (Human Nutrition: Clinical Nutrition, 1986; 40C: 81-6).