Myths and misconceptions about the causes of breast cancer
Does the immune system have a role?
It is a common community view that cancer is due to a failure in the body’s immune system, or a loss of the body’s defense system. This may play a minor role, but for breast cancer in young healthy women, it is probably almost irrelevant. We don’t see epidemics of breast cancer in people who have their immune system suppressed for long periods in order to allow them to have organ transplantation, for instance. And there have been no reproducible studies showing defects in the immune system in breast cancer patients.
Can I prevent breast cancer by taking substances that are thought to stimulate the immune system, like anti-oxidants?
No. I wish it were that easy! There is no known substance that prevents breast cancer in humans except for tamoxifen, an anti-oestrogen. Tamoxifen and other anti-oestrogens are under investigation for the prevention of breast cancer in women who are at high risk. There is no evidence that vitamins, antioxidants, selenium or any other agent reduces breast cancer risk in women who are taking a normal balanced healthy diet.
Is breast cancer due to stress?
No. Despite many investigations there is no evidence that breast cancer is linked to stress. Everyone can link the onset of any illness to some stressful event in their lives, but there is absolutely no evidence that stress is linked to the onset of breast cancer, although this remains one of the most widely-held community views. I think it is almost insulting to attribute such a serious and common complaint to something like “stress”. It must have been a hell of a lot more stressful living in the jungle, and it is certainly pretty stressful living in third world countries which have the lowest incidence of breast cancer.
Contrary to all the hype about stress and breast cancer risk, there is one very good study which shows that stress REDUCES breast cancer risk. Published in the British Medical Journal in September 2005, this study by Dr Nielsen and others looked at data from more than 6,600 women in Denmark. The women had enrolled in a long-term study of heart health.When the heart study started, the women were about 50 years old. They rated the intensity and frequency of their tension, nervousness, impatience, and sleeplessness as markers of stress. The women were followed for up to 18 years and during that time, 251 women had their first breast cancer diagnosis. Women who reported high stress levels at the study's start were 40% less likely to be diagnosed with breast cancer during the study than those who had reported low stress levels.
Does the dairy-free diet prevent breast cancer?
No. Claims to this effect are without scientific validity. No epidemiological study shows a link between dairy consumption and breast cancer risk.
The immense popularity of the book “Your Life in Your Hands” by Professor June Plant (published in 2000) has led to widespread belief that excluding dairy products from the diet can prevent and treat breast cancer.
Professor Plant, who is not a health professional, but a Professor of Geophysics, bases her claim largely on 1) correlation studies (Asians drink less milk, Asians have less breast cancer, therefore milk causes breast cancer), 2) personal testimony: her own breast cancer recurrence responded to elimination of dairy foods, and 3) the hypothetical link between hormones in milk and breast cancer biology.
Regrettably, there is no evidence to support the claims made in this book.
1) Correlation studies are notoriously misleading in medicine. For example, you might find that more people with red cars have breast cancer. This does not mean red cars cause breast cancer. It MIGHT mean that women with a certain hormonal makeup chose red cars, AND, quite separately, they have a greater incidence of breast cancer. But it could equally mean absolutely nothing.
2) Personal testimony is also very misleading in medicine. I have never seen confirmation of June Plant’s claim despite many patients trying it. I wish it were so simple!
3) There is evidence that high levels of growth factors in blood may be involved in causing breast cancer but there are many reasons for high blood levels. These include lack of physical activity and a high-energy diet (especially in the early teenage years); - these are already known risk factors for cancer. As there is not enough evidence that growth factors in milk can survive digestion in the human body, or that they can reach the bloodstream, this claim is as yet unsubstantiated.
The dairy story has been extensively investigated. When I was asked about it recently by one of my patients I checked with the best breast cancer epidemiologists in Australia.
Here is what Professor Beth Newman from Queensland University of Technology says:
“The best investigation is published in the International Journal of Epidemiology (Missmer SA, et al. Meat and dairy food consumption and breast cancer: A pooled analysis of cohort studies. Int J Epidemiol 2002; 31: 78-85). As the title suggests, it pools data from 8 prospective studies and comes to the conclusion that there is no significant association with intake of either meat or dairy food. It addresses dairy fluids and solids separately, and has sufficient numbers to look at specific dairy foods -- none of them show significant relative risks and most of the estimates cluster right around 1.0. Unfortunately, the paper is fairly jargonistic, so it might be a bit slow going for someone not familiar with the technical terminology.”
Beth also points out that the best review of the whole field of breast cancer and diet, which is in the textbook “Diseases of the Breast” (Editor Jay Harris) does not even mention dairy foods, because there simply is no evidence to support an association between them and breast cancer causation or progression.
The June Plant dairy-free diet is probably safe, providing that adequate calcium is taken, but there is nothing to recommend it, so I don’t.
See also my notes on Eating to be cancer free.
Does a meat-free diet prevent breast cancer?
No. Claims to this effect are without scientific validity. No epidemiological study shows a link between meat consumption and breast cancer risk.
Is breast cancer caused by a high fat diet?
Despite earlier suggestions from animal studies and some smaller human studies, carefully conducted prospective clinical studies provide strong evidence that no major relation exists between total dietary fat intake and breast cancer incidence over a wide range during midlife. It remains possible that dietary fat intake during childhood or early adult life may affect breast cancer risk in late adulthood, but no evidence exists to support this.
Do soy products protect against breast cancer?
Products of the soy bean including soy milk, contain compounds called phytoestrogens. These compounds, which include daidzen and genistein, can bind estrogen receptors. Theoretically, these compounds could inhibit estrogens and thereby reduce breast cancer risk. However, the two best clinical studies conducted so far show no evidence of any protective effect of soy products. Also, soy consumption is not the main explanation for low rates of breast cancer in Japan and China, because rates are similarly low in some parts of China, elsewhere in Asia, and in many developing countries in which soy and related foods are not consumed regularly. I do not recommend the consumption of large amounts of soy products because of the theoretical possibility that phytoestrogens could stimulate breast cancer cells in post-menopausal women.
Do under-arm deodorants cause breast cancer?
“Are you serious?”, I hear you say!
Well, you’d be amazed at how many people believe this one. It seems to have arisen in an e-mail hoax in the early 1990s and rapidly became an urban myth. The notion is that aluminium salts enter through the skin and somehow become concentrated in the breast, somehow resulting in cancer.
Two recent epidemiological studies purported to show a link between excessive antiperspirant use, frequent shaving and breast cancer. They have both been firmly discredited by epidemiologists as being underpowered and not having appropriate controls.
Finding causative links between environmental factors and disease is notoriously difficult.
My advice: there is no evidence of any link between breast cancer and the use of under-arm deodorants, or shaving.
Looking for more information?
Cancer Australia have recently launched a website detailing risk factors, protective factors and unproven factors associated with breast cancer. Check out the website here.
It is a common community view that cancer is due to a failure in the body’s immune system, or a loss of the body’s defense system. This may play a minor role, but for breast cancer in young healthy women, it is probably almost irrelevant. We don’t see epidemics of breast cancer in people who have their immune system suppressed for long periods in order to allow them to have organ transplantation, for instance. And there have been no reproducible studies showing defects in the immune system in breast cancer patients.
Can I prevent breast cancer by taking substances that are thought to stimulate the immune system, like anti-oxidants?
No. I wish it were that easy! There is no known substance that prevents breast cancer in humans except for tamoxifen, an anti-oestrogen. Tamoxifen and other anti-oestrogens are under investigation for the prevention of breast cancer in women who are at high risk. There is no evidence that vitamins, antioxidants, selenium or any other agent reduces breast cancer risk in women who are taking a normal balanced healthy diet.
Is breast cancer due to stress?
No. Despite many investigations there is no evidence that breast cancer is linked to stress. Everyone can link the onset of any illness to some stressful event in their lives, but there is absolutely no evidence that stress is linked to the onset of breast cancer, although this remains one of the most widely-held community views. I think it is almost insulting to attribute such a serious and common complaint to something like “stress”. It must have been a hell of a lot more stressful living in the jungle, and it is certainly pretty stressful living in third world countries which have the lowest incidence of breast cancer.
Contrary to all the hype about stress and breast cancer risk, there is one very good study which shows that stress REDUCES breast cancer risk. Published in the British Medical Journal in September 2005, this study by Dr Nielsen and others looked at data from more than 6,600 women in Denmark. The women had enrolled in a long-term study of heart health.When the heart study started, the women were about 50 years old. They rated the intensity and frequency of their tension, nervousness, impatience, and sleeplessness as markers of stress. The women were followed for up to 18 years and during that time, 251 women had their first breast cancer diagnosis. Women who reported high stress levels at the study's start were 40% less likely to be diagnosed with breast cancer during the study than those who had reported low stress levels.
Does the dairy-free diet prevent breast cancer?
No. Claims to this effect are without scientific validity. No epidemiological study shows a link between dairy consumption and breast cancer risk.
The immense popularity of the book “Your Life in Your Hands” by Professor June Plant (published in 2000) has led to widespread belief that excluding dairy products from the diet can prevent and treat breast cancer.
Professor Plant, who is not a health professional, but a Professor of Geophysics, bases her claim largely on 1) correlation studies (Asians drink less milk, Asians have less breast cancer, therefore milk causes breast cancer), 2) personal testimony: her own breast cancer recurrence responded to elimination of dairy foods, and 3) the hypothetical link between hormones in milk and breast cancer biology.
Regrettably, there is no evidence to support the claims made in this book.
1) Correlation studies are notoriously misleading in medicine. For example, you might find that more people with red cars have breast cancer. This does not mean red cars cause breast cancer. It MIGHT mean that women with a certain hormonal makeup chose red cars, AND, quite separately, they have a greater incidence of breast cancer. But it could equally mean absolutely nothing.
2) Personal testimony is also very misleading in medicine. I have never seen confirmation of June Plant’s claim despite many patients trying it. I wish it were so simple!
3) There is evidence that high levels of growth factors in blood may be involved in causing breast cancer but there are many reasons for high blood levels. These include lack of physical activity and a high-energy diet (especially in the early teenage years); - these are already known risk factors for cancer. As there is not enough evidence that growth factors in milk can survive digestion in the human body, or that they can reach the bloodstream, this claim is as yet unsubstantiated.
The dairy story has been extensively investigated. When I was asked about it recently by one of my patients I checked with the best breast cancer epidemiologists in Australia.
Here is what Professor Beth Newman from Queensland University of Technology says:
“The best investigation is published in the International Journal of Epidemiology (Missmer SA, et al. Meat and dairy food consumption and breast cancer: A pooled analysis of cohort studies. Int J Epidemiol 2002; 31: 78-85). As the title suggests, it pools data from 8 prospective studies and comes to the conclusion that there is no significant association with intake of either meat or dairy food. It addresses dairy fluids and solids separately, and has sufficient numbers to look at specific dairy foods -- none of them show significant relative risks and most of the estimates cluster right around 1.0. Unfortunately, the paper is fairly jargonistic, so it might be a bit slow going for someone not familiar with the technical terminology.”
Beth also points out that the best review of the whole field of breast cancer and diet, which is in the textbook “Diseases of the Breast” (Editor Jay Harris) does not even mention dairy foods, because there simply is no evidence to support an association between them and breast cancer causation or progression.
The June Plant dairy-free diet is probably safe, providing that adequate calcium is taken, but there is nothing to recommend it, so I don’t.
See also my notes on Eating to be cancer free.
Does a meat-free diet prevent breast cancer?
No. Claims to this effect are without scientific validity. No epidemiological study shows a link between meat consumption and breast cancer risk.
Is breast cancer caused by a high fat diet?
Despite earlier suggestions from animal studies and some smaller human studies, carefully conducted prospective clinical studies provide strong evidence that no major relation exists between total dietary fat intake and breast cancer incidence over a wide range during midlife. It remains possible that dietary fat intake during childhood or early adult life may affect breast cancer risk in late adulthood, but no evidence exists to support this.
Do soy products protect against breast cancer?
Products of the soy bean including soy milk, contain compounds called phytoestrogens. These compounds, which include daidzen and genistein, can bind estrogen receptors. Theoretically, these compounds could inhibit estrogens and thereby reduce breast cancer risk. However, the two best clinical studies conducted so far show no evidence of any protective effect of soy products. Also, soy consumption is not the main explanation for low rates of breast cancer in Japan and China, because rates are similarly low in some parts of China, elsewhere in Asia, and in many developing countries in which soy and related foods are not consumed regularly. I do not recommend the consumption of large amounts of soy products because of the theoretical possibility that phytoestrogens could stimulate breast cancer cells in post-menopausal women.
Do under-arm deodorants cause breast cancer?
“Are you serious?”, I hear you say!
Well, you’d be amazed at how many people believe this one. It seems to have arisen in an e-mail hoax in the early 1990s and rapidly became an urban myth. The notion is that aluminium salts enter through the skin and somehow become concentrated in the breast, somehow resulting in cancer.
Two recent epidemiological studies purported to show a link between excessive antiperspirant use, frequent shaving and breast cancer. They have both been firmly discredited by epidemiologists as being underpowered and not having appropriate controls.
Finding causative links between environmental factors and disease is notoriously difficult.
My advice: there is no evidence of any link between breast cancer and the use of under-arm deodorants, or shaving.
Looking for more information?
Cancer Australia have recently launched a website detailing risk factors, protective factors and unproven factors associated with breast cancer. Check out the website here.