Breast cancer is the most common cancer in women, and it is the second leading cause of female cancer deaths. Risk factors for breast cancer have been extensively studied, and data is still emerging. A number of risk factors and theories for the development of breast cancer have been developed, and the data at times show conflicting results. Cancer rates vary by race and by region, with higher rates in Europe and the US compared to lower rates in Asia and Africa. Certain dietary and lifestyle issues have been looked at in regard to breast cancer risk, and an attempt will be made to address lifestyle and dietary changes that can be made in an attempt to lower breast cancer risk.
There is one risk factor for the development of breast cancer on which most people agree. That would be prolonged and continuous estrogen stimulation (i.e. production) to the breast. The only disagreement seems to be in the degree of that risk, which seems to be higher for some women than for others. The idea of prolonged and continuous estrogen stimulation as a risk factor comes from the finding of an increase in breast cancer in women who:
- had early onset of menarche.
- had late onset of menopause.
- delayed having their first baby until after age 30.
Early menarche and late menopause contribute to the duration of estrogen stimulation, and a delayed pregnancy contributes to the amount of continuous estrogen stimulation, continuous meaning unopposed by prolonged progesterone stimulation such as in pregnancy. While late menopause is not a lifestyle choice, it is thought that the age of menarche, which has been gradually decreasing, has been influenced by dietary habits over the last hundred years with increasing amounts of calories coming from protein as opposed to non-protein sources. Childbirth is increasingly under our control, both to plan to have it and to not, resulting in increasing numbers of women delaying childbirth until after 40, contributing to the cycle of continuous and unopposed estrogen stimulation.
Obesity is generally regarded as a risk factor for breast cancer, although the mechanism does not carry uniform agreement. It is known that fatty tissues convert a hormone made by the adrenal glands, called androstenedione, to estrone, an estrogen. This is known as “peripheral conversion,” in the sense that the adrenal hormone is converted to estrogen by the peripheral adipose tissues. The more adipose tissue, the higher the degree of peripheral conversion. This becomes especially important after menopause, a time when the ovarian production of estrogen stops. In this situation, obesity allows for continued estrogen stimulation through peripheral conversion, effectively prolonging the duration of prolonged and continuous estrogen stimulation. This effect seems especially important in central obesity, where the adipose tissue is primarily around the abdomen and midsection. Obesity in post-menopausal women is thought to be a cause of breast cancer more often than the use of menopausal estrogen replacement.
Despite the potential risks of estrogen replacement therapy, estrogen therapy provides enormous benefit, including a reduced risk of cardiovascular disease, prevention of osteoporosis, and relief of menopausal symptoms. The decision to take estrogen replacement therapy must be made on an individual basis, taking into account the benefit to be derived from estrogen replacement compared to the risks, including the risk of breast cancer. To assist in this decision, a mathematical model has been created to compute the risk of breast cancer for any given patient, taking into account information such as family history, age at first delivery, and so forth. This model is called the Gail Model Risk Factor Assessment, and can be used to weight the risk of breast cancer as a decision is made regarding estrogen replacement.
A number of dietary changes can be undertaken to lower the risk of developing breast cancer. Dietary consumption of antioxidant-containing foods, primarily fruits and vegetables, is thought to lower the risk of breast cancer. Cold water fish containing Omega-3 fatty acids are also thought to lower the risk, while consumption of foods containing Omega-6 fatty acids, primarily vegetable oils such as sunflower oil and corn oil, are thought to increase the risk. Soy consumption is currently in a controversy, as data from Asian countries show a low risk of breast cancer that has been attributed to their soy-based diet. In this country, however, there is concern that the ability soy has to mildly stimulate estrogen receptors may actually pose a risk. At this point, the concern is only theoretic, and data are still being gathered to evaluate the potential risk. As well, to achieve the same low level of breast cancer seen in Asia, soy must be consumed for a lifetime, not beginning later in life when awareness and concern set in.
Though it may seem like a stretch, bowel function, especially with regard to dietary fiber, may play a role in breast cancer. There is a process that occurs within the GI tract called the enterohepatic circulation. In this process, a variety of substances, including estrogen, are metabolized by the liver and excreted into the bile. From there, they are released into the GI tract and attached to dietary fiber, which is then excreted and removed from the body. If insufficient dietary fiber is present, the estrogen is then reabsorbed, effectively raising the level of estrogen, and possibly contributing to the development of breast cancer. For this reason, dietary fiber, particularly the insoluble kind, as is found in fruits and vegetables, is recommended as a means of reducing breast cancer risk.
A number of dietary and lifestyle issues are known to increase the risk of breast cancer. These would include, smoking, alcohol consumption, and the hyperinsulin state found in diabetes and obesity.