Breast cancer is the most common cancer in the UK. When this report was first published in 2006, the lifetime risk of being diagnosed with breast cancer was one in nine for UK women. In 2014, the figure is one in eight. That means one in every eight women in the UK will develop breast cancer at some point in their lives. In the UK in 2010 more than 49,500 women and around 400 men were diagnosed with breast cancer, that’s around 136 women per day and at least one man per day. Female breast cancer incidence rates in Britain have increased by almost70 per cent since the mid-1970s. Just in the last ten years they have gone up by six per cent.
Figure 5.0 shows that while the incidence of breast cancer has risen sharply, mortality from breast cancer has fallen (albeit relatively modestly) over the same period thanks largely to improved diagnostic methods and more efficient treatment.
Much has been made of the link between genes and breast cancer. However, only five to ten per cent of all breast cancers are thought to be linked to an inherited breast cancer gene. The genes BRCA1 and BRCA2 have received the most attention since they were first discovered in 1994 and 1995 respectively. Between 45 and 90 out of every 100 women carrying BRCA genes will get breast cancer at some point in their lives. We now know of other genes that significantly increase a woman's risk of breast cancer, they are called TP53 and PTEN. Researchers have found other genes that can slightly increase a woman's risk of developing breast cancer, they include: CASP8, FGFR2, TNRCP, MAP3K1, rs4973768, LSP1 and some rare genes that can also increase breast cancer risk slightly include: CHEK2, ATM (ataxia telangiectasia mutated), BRIP1 and PALB2 (MacMillan Cancer Support, 2011).
These discoveries linking genetics to cancer has given rise to a certain degree of genetic fatalism. However, as stated current estimates are that only around five to ten per cent of breast cancers are due to abnormal genes. This means that the vast majority of cancers (90-95 per cent) are not caused by abnormal genes. Secondly, it is important to remember that having an abnormal gene does not mean that a person will definitely develop breast cancer, but does mean they are considerably more at risk of developing the condition than someone who does not have one of the abnormal genes.
Lifestyle and environmental factors that can increase breast cancer risk include: age (the risk increases significantly as you get older), alcohol, obesity, early puberty, late menopause (women who have undergone the menopause have a lower risk of breast cancer than premenopausal women of the same age), late age at first childbirth, hormone replacement therapy (HRT) and the contraceptive pill. Factors that may decrease the risk include: younger age at first pregnancy (the younger the woman is when she begins childbearing, the lower her risk of breast cancer), breastfeeding, late puberty, early menopause and physical activity. The contribution of various environmental and lifestyle factors (excluding reproductive factors) to breast cancer risk has was calculated by a group from Harvard School of Public Health (Danaei et al., 2005). They conclude that 21 per cent of all breast cancer deaths worldwide are attributable to alcohol use, being overweight or obese and physical inactivity. This proportion is even higher (27 per cent) in high-income countries. That’s nearly a third of all breast cancer cases being attributed to avoidable risk factors.
Breast cancer incidence rates vary greatly worldwide, with age standardised rates as high as 99.4 per 100,000 in North America. Eastern Europe, South America, Southern Africa and Western Asia have moderate incidence rates, but these are increasing. The lowest rates are found in most African countries but here breast cancer incidence rates are also increasing (WHO, 2013a). Migration studies show us that this variation is not due to genetic factors and that environmental and lifestyle factors must be involved. Because of this, an increasing amount of attention has focused on the links between diet and breast cancer, particularly the relationship between the consumption of cow’s milk and dairy products and breast cancer.
Studying cancer incidence among particular groups of people can provide useful insights into the links between diet and disease. Researchers from the London School of Hygiene and Tropical Medicine recently reported breast cancer incidence is substantially lower, and survival rates higher, in South Asians living in the UK than other women (Farooq and Coleman, 2005). No data on diet was collected but the authors of this study suggested that differences in diet and lifestyle could explain the different rates observed. Earlier research published in the British Journal of Cancer also showed that South Asian women living in the UK are less likely to be diagnosed with breast cancer than other women, but found that the risk varied according to their specific ethnic subgroup. This research showed that Muslim women from India and Pakistan are almost twice as likely to develop breast cancer as Gujarati Hindu women. This study did examine the diet and found that the Gujarati Hindu women were more likely to be vegetarian and therefore had more fibre in their diet due to their higher intake of fruit and vegetables (McCormack et al., 2004). More recently, a prospective cohort study looked at the associations between plant foods, fibre and risk of breast cancer in 11,726 postmenopausal women in the Malmö Diet and Cancer cohort in Sweden among whom 342 incident cases of breast cancer were recorded. They found that a dietary pattern characterised by high fibre and low fat intakes was associated with a lower risk of postmenopausal breast cancer (Mattisson et al., 2009). There are several mechanisms by which fibre in the diet might influence breast cancer risk. One possible mechanism is through an effect on hormones: increasing the amount of fibre in the diet may reduce breast cancer risk by altering the levels of female hormones (oestrogens) circulating in the blood (Gerber, 1998).
A number of studies show that women with breast cancer tend to have higher levels of circulating oestrogens. A recent review of 13 studies concluded that circulating sex hormone concentrations in postmenopausal women are strongly associated with several established or suspected risk factors for breast cancer and may mediate the effects of these factors on breast cancer risk (Key et al., 2011). In other words, some environmental or lifestyle factors (for example, obesity or alcohol consumption) may increase the levels of hormones circulating in the body and this may lead to breast cancer in some people.
A prospective study conducted on the island of Guernsey examined serum levels of the oestrogen hormone oestradiol in samples taken from 61 postmenopausal women who developed breast cancer an average of 7.8 years after blood collection. Compared to 179 age-matched controls, oestradiol levels were 29 per cent higher in women who later developed breast cancer (Thomas et al., 1997). Another prospective study (this time from the US), compared oestrogen levels in 156 postmenopausal women who developed breast cancer, after blood collection, with two age-matched controls for each cancer patient. Results showed increased levels of the hormones oestradiol, oestrone, oestrone sulphate and dehydroepiandrosterone sulphate in women who subsequently developed breast cancer thus providing strong evidence for a causal relationship between postmenopausal oestrogen levels and the risk of breast cancer (Hankinson et al., 1998). A review of studies carried out over a 10 year period in the Department of Clinical Chemistry at the University of Helsinki in Finland suggested that the Western diet (characterised by milk and meat products) increases levels of these types of hormones and concluded that the hormone pattern found in connection with a Western-type diet is prevailing in breast cancer patients (Adlercreutz, 1990).
Researchers at the Department of Preventive Medicine at the University of Southern California Medical School in Los Angeles published a review of 13 dietary fat intervention studies that were conducted to investigate the effect of fat intake on oestrogen levels. The results showed decreasing dietary fat intake (to between 10 and 25 per cent of the total energy intake) reduced serum oestradiol levels by between 2.7 and 10.3 per cent. It was concluded that dietary fat reduction can result in a lowering of serum oestradiol levels and that such a dietary modification may offer an approach to breast cancer prevention (Wu et al., 1999). As stated, cow’s milk and dairy products are a major source of dietary saturated fat.
These early reports are supported by more recent research that examined postmenopausal breast cancer risk in women consuming two different dietary patterns in a large French cohort study. The ‘alcohol/Western’ diet included processed meat and meat products, ham, offal, French fries, appetisers, sandwiches, rice/pasta, potatoes, pulses, pizza/pies, canned fish, eggs, crustaceans, alcoholic beverages, cakes, mayonnaise, butter and cream and the ‘healthy Mediterranean’ diet was made up of a high intake of vegetables and fruits, fish and crustaceans, olives and sunflower oil. Results showed those eating the Western diet had a 20 per cent increased risk of breast cancer while those consuming the Mediterranean diet had a 15 per cent lower risk (Cottet et al., 2009).
Identifying the type of diet that can increase or reduce the risk of cancer is just part of the puzzle. Identifying which components of that diet are responsible is another matter of considerable complexity. While some research has identified dietary factors that reduce the risk of breast cancer, such as fibre, other studies have attempted to identify dietary factors that increase the risk, such as dietary fat. Case-control studies use a group of people with a particular characteristic (for example older women with lung cancer). This particular group is selected and information collected (for example, history of smoking), then a control group is selected from a similar population (older women without lung cancer) to see if they smoked or not, then a conclusion is drawn (smoking does or does not increase risk of lung cancer). A combined analysis of 12 case-control studies designed to examine diet and breast cancer risk found a positive association between fat intake and this disease. The reviewers estimated that the percentage of breast cancers that might be prevented by dietary modification in the North American population was 24 per cent for postmenopausal women and 16 per cent for premenopausal women (Howe et al., 1990). This is a significant number of cancers that could be prevented simply by changing the diet.
In a prospective cohort study involving over 90,000 premenopausal women, researchers from Harvard Medical School also found that animal fat intake was associated with an elevated risk of breast cancer. Red meat and high-fat dairy foods such as whole milk, cream, ice-cream, butter, cream cheese and cheese were the major contributors of animal fat in this cohort of relatively young women. Interestingly, this research did not find any clear association between vegetable fat and breast cancer risk; the increased risk was only associated with animal fat intake. It has been suggested that a high-fat diet increases the risk of breast cancer by elevating concentrations of oestrogen. However, the author of this study, Dr Eunyoung Cho, suggests that if this were true a diet high in animal fat and a diet high in vegetable fat should both lead to higher rates of cancer, and that was not the case in this study. Cho suspects that some other component such as the hormones in cow’s milk might play a role in increasing the risk of breast cancer (Cho et al., 2003). A subsequent meta-analysis of all papers published up to July 2003 that examined the association of dietary fat with risk of breast cancer also found a positive association between higher intakes of fat and an increased risk of breast cancer (Boyd et al., 2003).
However, other studies of fat intake and the incidence of breast cancer have yielded conflicting results. The discrepancy in results may reflect the difficulties of accurately recording fat intake. Dr Sheila Bingham of the Dunn Human Nutrition Unit in Cambridge developed a data-collection method to overcome these problems. Bingham used food frequency questionnaire methods with a detailed seven-day food diary in over 13,000 women between 1993 and 1997. The study concluded that those who ate the most animal saturated fat (found mainly in whole milk, butter, meat, cakes and biscuits) were almost twice as likely to develop breast cancer as those who ate the least. It was also concluded that previous studies may have failed to establish this link because of imprecise methods (Bingham et al., 2003). That said, a recent study using data from four prospective cohort studies in the United Kingdom (EPIC-Norfolk , EPIC-Oxford, the UKWCS and Whitehall II study) found no association between dietary fat and breast cancer (Key et al., 2011a). These researchers were aware of the methodology problems identified by Bingham and could not identify any reason why their results were different from those of Bingham’s group. More research is needed to clarify the role of total fat and saturated fat in breast cancer.
Some research groups are more interested in the endogenous hormonal content of milk (hormones produced by the cow and excreted in the milk), which has not been widely discussed. The milk produced now is very different from that produced 100 years ago; modern dairy cows are impregnated while still producing milk (Webster, 2005). Two thirds of milk in the UK is taken from pregnant cows with the remainder coming from cows that have recently given birth. This means that the hormone (oestrogen, progesterone and androgen precursor) content of milk varies widely. It is the high levels of hormones in milk that have been linked to the development of hormone-dependent cancers such as ovarian and breast cancer.
In a review of the relationship between breast cancer incidence and food intake among the populations of 40 different countries, a positive correlation was seen between the consumption of meat, milk and cheese and the incidence of breast (and ovarian) cancer. Meat was most closely correlated with breast cancer incidence, followed by cow’s milk and cheese. By contrast, cereals and pulses were negatively correlated with the incidence of breast cancer. This review concluded that the increased consumption of animal foods may have adverse effects on the development of hormone-dependent cancers. Among dietary risk factors of particular concern were milk and dairy products, because so much of the milk we drink today is taken from pregnant cows, in which oestrogen and progesterone levels are markedly elevated (Ganmaa and Sato, 2005). Commercial milk products have been shown to contain considerable levels of oestrogen metabolites (Farlow et al., 2009). This raises concerns that the high levels of oestrogen metabolites and other bioactive molecules in milk may influence cancer risk.
In a review of the evidence linking dairy consumption to breast cancer risk, researchers from Princeton University in New Jersey concluded that milk may promote breast cancer by the action of the growth factor IGF-1, which has been shown to stimulate the growth of human breast cancer cells in the laboratory (Outwater et al., 1997). In another review, examining the role of IGF-1 in cancer development, Yu and Rohan state that IGFs play a critical role in regulating cell growth and death. This function has led to speculation about their involvement in cancer development. Laboratory experiments demonstrate the ability of IGFs to stimulate growth of a wide range of cancer cells and to suppress cell death or apoptosis (Yu and Rohan, 2000). The concern here is that if IGF-1 can cause human cancer cells to grow in a Petri dish in the laboratory, they might have a cancer-inducing effect when consumed in the diet. Furthermore, cow’s milk is known to increase IGF-1 levels in the blood by driving up IGF-1 production by the liver.
IGF-1 is present in all milk and is not destroyed during pasteurisation. Dr J.L. Outwater of the Physicians Committee For Responsible Medicine (PCRM) in Washington, DC, warns that IGF-1 may be absorbed across the gut and cautions that regular milk ingestion after weaning may produce enough IGF-1 in mammary tissue to encourage cell division thus increasing the risk of cancer (Outwater et al., 1997). However, other scientists contest this view and say that IGF-1 could not cross the gut wall at sufficient levels to alter systemic levels already circulating but do say that there are many small peptides and amino acids that are present in milk that potently stimulate hepatic IGF-1 expression and pituitary growth hormone release (Holly, 2013). In either scenario, the net effect is the same; cow’s milk consumption raises IGF-1 levels in humans and higher IGF-1 levels are linked to cancers of the colon, prostate and breast.
In her book Your Life in Your Hands, Professor Jane Plant CBE, the chief scientist of the British Geological Survey, describes a very personal and moving story of how she overcame breast cancer by excluding all dairy products from her diet (Plant, 2007). Plant was diagnosed with breast cancer in 1987. She had five recurrences of the disease and by 1993 the cancer had spread to her lymphatic system. She could feel the lump on her neck, and was told that she had just three months to live, six if she was lucky. However, Plant was determined to use her scientific training to find a solution to this ‘problem’. She began researching breast cancer in other cultures and found a much lower incidence in China. The data showed that in rural China breast cancer affects just one in 10,000 women compared to one in 10 British women (now one in eight). However, Plant observed that among wealthy Chinese women with a more Western lifestyle (for example in Malaysia and Singapore), the rate of breast cancer is similar to that in the West. Furthermore, epidemiological evidence shows that when Chinese women move to the West, within one or two generations their rates of breast cancer incidence and mortality increase to match those of their host country. This suggested that diet and lifestyle (rather than genetics) must be a major determinant of cancer risk.
Plant decided to investigate the role of diet in breast cancer risk. She examined the results of the China-Cornell-Oxford project on nutrition, environment and health (Campbell and Junshi, 1994). This project was based on national surveys conducted between 1983 and 1984 in China. The project was a collaboration between T. Colin Campbell at Cornell University in the US, Chen Junshi from the Chinese Academy of Preventative Medicine, in Beijing, China, Li Junyao at the Chinese Academy of Medical Sciences, Beijing, and Richard Peto from Oxford University in the UK. The project revealed some surprising insights into diet and health. For example, it showed that people in China tend to consume more calories per day that people in the US, but only 14 per cent of these calories come from fat compared to a massive 36 per cent in the West. This coupled to the fact that Chinese people tend to be more physically active than people in the West, is why obesity affects far more people in the West than in China. However, Plant’s diet had not been particularly high in fat; indeed she describes it as very low in fat and high in fibre. Then Plant had a revelation: the Chinese don’t eat dairy produce. Plant had been eating yogurt and skimmed organic milk up until this time, but within days of ceasing all dairy, the lump on her neck began to shrink. The tumour decreased and eventually disappeared, leading her to the conviction that there is a causal link between the consumption of dairy products and breast cancer. Although Plant received chemotherapy during this time, it did not appear to be working and so convinced was her cancer specialist that it was the change in diet that saved her life, he now refers to cancer mortality maps in his lectures and recommends a dairy-free diet to his breast cancer patients.
Plant eventually defeated cancer by eliminating dairy products from her diet, replacing them with healthy alternatives and making some lifestyle changes. At the time of writing (2007) Plant had been cancer-free for 14 years and now advises that if you do only one thing to cut your risk of breast cancer, make the change from dairy to soya (Plant, 2007).
A meta-analysis of the effects of soya on breast cancer found a mildly protective rather than deleterious effect in premenopausal women (Trock et al., 2006) and more recently a paper from the Shanghai Breast Cancer study also indicated somewhat better outcomes related to soya consumption in woman with established breast cancer Shu et al., 2009). Providing breast cancer patients with sound dietary advice could greatly increase survival rates. Taken together, these observations show that a dairy-free plant-based diet can reduce many of the risk factors associated with breast cancer and may help those who have been diagnosed with the disease.