The incidence of postmenopausal breast cancer varies dramatically from one part of the world to the other, and those who move from one country to another will, on average, over time, begin to take on the risk of the new society to which they have moved. This evidence strongly suggests that most, though not all, breast cancer is preventable. However, great controversy exists about which factors are most responsible for the large differences in breast cancer incidence that separate high-risk populations from low-risk populations.
A few factors that affect the risk of having breast cancer are widely accepted:
Several other factors may affect a woman’s risk of getting breast cancer. Many researchers and some doctors believe that long-term (greater than five years) use of oral contraceptives increases the risk of pre-menopausal breast cancer, but not the risk of postmenopausal breast cancer. Also, being overweight appears to slightly reduce the risk of pre-menopausal breast cancer, even though it increases the risk of postmenopausal breast cancer.
Almost all women with non-invasive breast cancer (ductal carcinoma in situ), along with a majority of women diagnosed with node-negative invasive breast cancer, are cured with appropriate conventional treatment. Even when breast cancer is diagnosed after it has spread to lymph nodes, many patients are curable. Once breast cancer has spread to a distant part of the body, conventional treatment sometimes extends life but cannot provide a cure.
What are the symptoms of breast cancer?
The diagnosis of breast cancer is usually begun at the time a painless one-sided lump is discovered by the woman or her physician. In recent years, the diagnosis of breast cancer often begins with suspicious findings from a routine screening mammogram accompanied by no symptoms. In more advanced cases, changes to the contour of the affected breast may occur, and the lump may eventually become immovable.
If breast cancer spreads to a distant part of the body (distal metastasis), symptoms are determined by the location to which the cancer has spread. For example, if breast cancer spreads to bone, it frequently causes bone pain; if it spreads to the brain, it generally causes neurological symptoms, such as headaches that do not respond to aspirin. When it has spread to a distant part of the body, breast cancer also eventually causes severe weight loss, untreatable fatigue-inducing anaemia, and finally death.
Dietary changes that may be helpful
The following dietary changes have been studied in connection with breast cancer.
Avoidance of alcohol
An analysis of studies using the best available methodology found that women who drink alcohol have a higher risk of breast cancer compared with teetotallers. Alcohol consumption during early adulthood may be more of a risk factor than alcohol consumption at a later age.
Some, though not all, studies have reported that alcohol increases oestrogen levels. Increased oestrogen levels might explain the increase in risk.
In a preliminary report, drinkers with low intake of folic acid had a 32% increased risk of breast cancer compared with non-drinkers; however, the excess risk was only 5% in those drinkers who consumed adequate levels of folic acid. In the same report, women taking multivitamins containing folic acid and having at least 1.5 drinks per day had a 26% lower risk of being diagnosed with breast cancer compared with women drinking the same amount of alcohol but not taking folic acid-containing vitamins.
Fibre
Insoluble fibre from grains delays the onset of mammary (breast) cancer in animals. In an analysis of the data from many studies, people who eat relatively high amounts of whole grains were reported to be at low risk for breast cancer.
In some studies, the protective effect of fibre against the risk of breast cancer has been stronger in young women than in older women. This finding might occur because fibre has been reported to lower oestrogen levels in pre-menopausal women but not in postmenopausal women. Other researchers, however, report that fibre appears to equally reduce the risk of breast cancer in women of all ages. One leading researcher has suggested the active components in fibre may be phytate and isoflavones, substances that may provide protection even in the absence of a decrease in oestrogen levels. If these substances do protect against breast cancer, they might be as helpful in older women as in younger women.
Consuming a diet high in insoluble fibre is best achieved by switching from white rice to brown rice and from bakery goods made with white flour or mixed flours to 100% whole wheat bread, whole rye crackers, and whole grain pancake mixes. Refined white flour is generally listed on food packaging labels as “flour,” enriched flour,” unbleached flour,” durum wheat,” semolina,” or “white flour.” Breads containing only whole wheat are usually labelled “100% whole wheat.”
Vegetarianism
Compared with meat eaters, most, but not all, studies have found that vegetarians are less likely to be diagnosed with cancer. Vegetarians have also been shown to have stronger immune functioning, possibly explaining why vegetarians may be partially protected against cancer. Female vegetarians have been reported to have lower oestrogen levels compared with meat-eating women, possibly explaining a lower incidence of breast cancer that has been reported in vegetarian women.
Fruits and vegetables
An analysis of 17 studies on breast cancer risk and diet found that high consumption of vegetables was associated with a 25% decreased risk of breast cancer compared with low consumption. The same report analyzed 12 studies that found high consumption of fruit was associated with a 6% reduction of breast cancer incidence compared with low consumption. However, when data from only the eight largest and best studies were combined, high intake of fruits and/or vegetables did not correlate with protection from breast cancer. Therefore, the protective effect of fruit and vegetable consumption against breast cancer remains unproven.
Tomatoes
Tomatoes contain lycopene—an antioxidant similar in structure to beta-carotene. Most lycopene in our diet comes from tomatoes, though traces of lycopene exist in other foods. Lycopene has been reported to inhibit the proliferation of cancer cells in test tube research.
A review of published research found that higher intake of tomatoes or higher blood levels of lycopene correlated with a reduced risk of a variety of cancers in 57 of 72 studies. Findings in 35 of these studies were statistically significant. Evidence of a protective effect for tomato consumption was strongest for cancers other than breast cancer (prostate, lung, and stomach cancer), but some evidence of a protective effect also appeared for breast cancer.
Meat and how it is cooked
Most, but not all, studies show that consumption of meat is associated with an increased risk of breast cancer. This association probably depends in part on how well the meat is cooked. Well-done meat contains more carcinogenic material than does lightly cooked meat. Evidence from preliminary studies shows that women who eat well-done meat have a high risk of breast cancer. Genetic factors may determine which women increase their risk of breast cancer by eating well-done meat.
Fish
Fish eaters have been reported to have a low risk of breast cancer. The omega-3 fatty acids found in fish are thought by some researchers to be the components of fish responsible for protection against cancer.
Coffee, unrelated to risk
Coffee drinking has been reported to increase breast pain associated with no cancerous lumps in the breast—a group of conditions commonly called fibrocystic breast disease.
The presence of some forms of fibrocystic breast disease has been reported by some researchers to increase the risk of breast cancer. As a result of these separate findings, some women may be concerned coffee drinking might increase the risk of breast cancer. However, most research has shown that coffee drinkers are at no higher risk of breast cancer than are women who do not drink coffee.
Olive oil
Olive oil consumption has been associated with a reduced risk of breast cancer in several preliminary reports. Oleic acid, the main fatty acid found in olive oil, does not appear to be the cause of this protective effect, and scientists now guess that some as– yet undiscovered substance in olive oil might be responsible for the apparent protective effect of olive oil consumption.
The dilemma over dietary fat
Olive oil and fish are two sources of dietary fat considered potentially helpful in protecting against breast cancer. Each has been discussed separately above. The information below discusses fat sources that some researchers are concerned might increase the risk of cancer.
High-fat diets increase the risk of mammary cancer in animals. From country to country, breast cancer risk in women is proportionate to the level of total fat consumed in the diet. Oestrogen levels, body weight, and breast density have all been reported to decrease when women are put on low-fat diets—all changes that are thought to reduce the risk of breast cancer. Moreover, breast cancer patients have been reported to reduce their chances of survival by eating a diet high in saturated fat. (Saturated fat is found mostly in meat and dairy fat.) Similarly, breast cancer patients have been reported to be at increased risk of suffering a recurrence if they eat higher levels of fatty foods, such as butter, margarine, red meat, and bacon.
Analysis of human trials, using a research design dependent on the memories of subjects, also has shown women consuming high-fat diets to be at high risk of breast cancer. In some cases, the correlation has been quite strong. However, most, but not all, “prospective” studies—which avoid problems caused by faulty memories—have not found any association between fat intake and the risk of breast cancer.
Why do some research findings suggest that fat increases the risk of cancer and other studies find no association? Some studies finding dietary fat unrelated to cancer risks have not factored out the effects of olive oil or fish fat; both may protect against cancer. Adding them to the total dietary fat intake and then studying whether “more fat causes more cancer” is therefore misleading. Some studies finding no association between fat intake and breast cancer have made one or both of these errors.
Scientists know cancers caused by diet most likely occur many years after the causative foods are regularly consumed. When one group of researchers compared dietary intakes to cancer rates occurring ten years after the consumption of food, and also eliminated from consideration the effect of fat from fish consumption, they found a high degree of correlation between consumption of animal fat (other than from fish) and the risk of breast cancer death rates for women at least 50 years of age.
In the debate over whether dietary fat increases breast cancer risks, only one fact is indisputable: women in countries that consume high amounts of meat and dairy fat have a high risk of breast cancer, while women in countries that mostly consume rice, soy, vegetables, and fish (instead of dairy fat and meat) have a low risk of breast cancer.
The complex relationship between soy consumption and risk
Asian countries in which soy consumption is high generally have a low incidence of breast cancer. However, the dietary habits in these countries are so different from diets in high-risk countries that attributing protection from breast cancer specifically to soy foods on the basis of this evidence alone is premature. Similarly, within a society, women who frequently consume tofu have been reported to be at low risk of breast cancer. Consumption of tofu might only be a marker for other dietary or lifestyle factors that are responsible for protection against breast cancer.
Genistein, one of the isoflavones found in many soy foods, inhibits proliferation of breast cancer cells in test tube studies. Most animal studies report that soybeans and soy isoflavones protect against mammary cancer. However, the protective effect in animals has occurred primarily when soy has been administered before puberty. If the same holds true in humans, consuming soy products in adulthood might provide little, if any, protection against breast cancer.
The findings of several recent studies suggest that consuming soy might, under some circumstances, increase the risk of breast cancer. When ovaries were removed from animals—a situation related to the condition of women who have had a total hysterectomy—dietary genistein was reported to increase the proliferation of breast cancer cells. When pregnant rats were given genistein injections, their female offspring were reported to be at greater risk of breast cancer. Although pre-menopausal women have shown decreases in oestrogen levels in response to soy consumption, pro- oestrogenic effects have also been reported. When pre-menopausal women were given soy isoflavones, an increase in breast secretions resulted—an effect thought to elevate the risk of breast cancer. In yet another trial, healthy breast cells from women previously given soy supplements containing isoflavones showed an increase in proliferation rates—an effect that might also increase the risk of breast cancer.
The commonly held belief that consuming soybeans or isoflavones such as genistein will protect against breast cancer is, therefore, far from proven. Possibly, consuming soybeans in childhood may ultimately be proven to have a protective effect. Doing the same in adulthood, however, may have very different effects.
Some scientists, at least under some circumstances, remain hopeful about the potential for soy to protect against breast cancer. These scientists recommend consumption of foods made from soy (such as tofu), as opposed to taking isoflavone supplements. Several substances in soybeans other than isoflavones have shown anticancer activity in preliminary research.
Reduction in sugar
Preliminary studies have reported associations between an increased intake of sugar or sugar-containing foods and an increased risk of breast cancer, though this link does not appear consistently in published research. Whether these associations exist because sugar directly promotes cancer or because sugar consumption is only a marker for some other dietary or lifestyle factor remains unknown.
Lifestyle changes that may be helpful
The following lifestyle changes have been studied in connection with breast cancer.
Exercise and prevention
Girls who engage in a significant amount of exercise have been reported to be less likely to get breast cancer as adults. Although some doctors speculate that exercise in preadolescent girls might reduce the risk of eventually getting breast cancer by reducing the number of menstrual cycles and therefore exposure to oestrogen, these effects may occur only in girls engaging in very strenuous exercise.
Most, but not all, studies find that adult women who exercise are less likely to get breast cancer. Women who exercise have also been reported to have a reduced risk of high- risk mammography patterns compared with inactive women.
Exercise in adulthood might help protect against breast cancer by lowering blood levels of oestrogen or by helping maintain ideal body weight. In addition to the preventive effects of exercise, aerobic exercise has been reported to reduce depression and anxiety in women already diagnosed with breast cancer.
Smoking and risk
Some studies have found an association between smoking and an increased risk of breast cancer, including exposure to second-hand smoke. However, several reports have either found no association or have reported an association between smoking and an apparent protection against breast cancer. Some of the studies reporting that smoking is detrimental have found that exposure to cigarette smoke during childhood appears to be most likely to increase the risk of breast cancer.
The mind-body connection
In some studies, the risk of breast cancer has been reported to be higher in women who have experienced major (though not minor) depression in the years preceding diagnosis. Some, but not all, studies have found that exposure to severely stressful events increases a woman’s chance of developing breast cancer. In one study, breast cancer patients exposed to severely stressful events, such as death of a spouse or divorce, had more than five times the risk of suffering a recurrence compared with women not exposed to such stressors. Although stress has long been considered as a possible risk factor, some studies have not found significant correlations between psychological stressors and breast cancer risk or the risk of breast cancer recurrence. Similarly, experiencing psychological distress (independent of external stressors) has, in some reports, not been associated with a reduction in survival or the risk of suffering a breast cancer recurrence.
Exposure to psychological stress has been reported to weaken the immune system of breast cancer patients. Strong social support has been reported to increase immune function in breast cancer patients. These findings suggest a possible way in which the mind might play a role in affecting the risk of a breast cancer recurrence.
In one study, breast cancer patients with strong social support in the months following surgery had only half the risk of dying from the disease during a seven-year period compared with patients who lacked anyone to confide in. After 10 and 15 years, breast cancer patients with a helpless and hopeless attitude or with an attitude of stoicism were much less likely to survive compared with women who had what the researchers called a “fighting spirit.” In a five-year study, the same helpless/hopeless attitude correlated with an increased risk of recurrence or death in breast cancer patients, but a “fighting spirit” did not correlate with special protection against recurrence or death. One trial reported that psychological therapy for hopeless/helpless breast cancer patients was capable of changing these attitudes and reducing psychological distress in only eight weeks.
Several trials using a variety of psychological interventions have reported increased life expectancy in women receiving counseling or psychotherapy compared with women who did not receive psychological intervention —even in women with late-stage disease. In a now-famous trial, late-stage breast cancer patients in a year-long, 90-minute-per- week support group lived on average twice as long as a group of similar patients who did not receive such support.
Finally, relaxation training has been reported to reduce psychological distress in breast cancer patients, and group therapy and hypnosis have reduced pain in late-stage breast cancer patients.
Even extensive psychological support (weekly peer support, family therapy, individual counseling, and use of positive mental imagery) has not led to a clear increase in breast cancer survival in every study. Why some studies clearly find mind-body connections in regard to breast cancer risk, recurrence, or survival, while other studies find no such connection, remains unclear.
Overweight and risk
Being overweight increases the risk of postmenopausal breast cancer, a fact widely accepted by the research community. Overweight does not increase the risk of pre– menopausal breast cancer and even may be associated with a slightly reduced risk of breast cancer in young women.
Nutritional supplements that may be helpful
The following nutritional supplements have been studied in connection with breast cancer.
Folic acid
Among women who drink alcohol, those who consume relatively high amounts of folate from their diet have been reported to be at reduced risk of breast cancer, compared with women who drink alcohol but consumed less folate, according to a preliminary study. In a similar report, consumption of folic acid-containing supplements was associated with a lower risk of breast cancer in women who drank alcohol, compared with women who drank alcohol but did not take such supplements.
The damaging effect alcohol has on DNA—the material responsible for normal replication of cells—is partially reversed by folic acid. Therefore, a potential association between both dietary folate and folic acid supplements and protection against breast cancer in women who drink alcohol is consistent with our understanding of the biochemical effects of these substances. A combined intake from food and supplements of at least 600 mcg per day was associated with a 43% reduced risk of breast cancer in women who consumed 1.5 drinks per day or more, compared with women who drank the same amount but did not take folic acid-containing supplements.
No research has yet explored the effect of folic acid supplementation in people who have already been diagnosed with cancer. Cancer patients taking the chemotherapy drug methotrexate must not take folic acid supplements without the direction of their oncologist.
Selenium
The association between relatively higher blood levels of selenium and lower risks of cancer in men has been fairly consistent. However, most, though not all, studies have found selenium status to be unrelated to cancer risk in women, particularly in relation to cancers that strike only women. In fact, a few studies have reported that exposure to higher amounts of selenium —including selenium from supplements —are associated with a higher risk of several cancers in women, though these studies have been criticized.
In a famous double-blind trial that reported dramatic reductions in the incidence of lung, colon, and prostate cancers as a result of selenium supplementation, of the few women who got breast cancer during the trial, more were taking selenium than were taking placebo, though this difference may well have been due to chance. Thus, the findings of this famous trial also do not support the idea that selenium supplementation protects against breast cancer.
In contrast, animal studies generally find that selenium helps protect against mammary cancer, and associations between higher selenium status and decreased risk of breast cancer in women have also occasionally been reported. Despite these hopeful findings, most studies suggest that higher selenium status confers no protection against breast cancer.
Vitamin E
Although some preliminary evidence suggests that vitamin E may protect against breast cancer, most research does not suggest a protective effect. In a preliminary study, women taking vitamin E supplements had the same risk of breast cancer as did other women. However, in one study, women with of low blood levels of both selenium and vitamin E had a tenfold higher risk of breast cancer compared with women having higher levels of both nutrients. Although vitamin E and selenium function together in the body, the meaning of this dramatic finding is not clear; most studies examining the effects of vitamin E or selenium separately have suggested that neither protects against breast cancer.
Although one form of vitamin E—alpha tocopheryl succinate—has been touted as a potential treatment for women with breast cancer, only test tube studies suggest that it may have anticancer activity, and no trials have been conducted in breast cancer patients.
Vitamin D
Breast cancer rates have been reported to be relatively high in areas of low exposure to sunlight. Sunlight triggers the formation of vitamin D in the skin, which can be activated in the liver and kidneys into a hormone with great activity. This activated form of vitamin D causes “cellular differentiation”—essentially the opposite of cancer.
The following evidence indicates that vitamin D might have a protective role against breast cancer:
Activated vitamin D
Activated vitamin D comes in several forms. One of them—1,25 dihydroxycholecalciferol—is an exact duplicate of the hormone made in the human body.
The following preliminary, non-clinical evidence supports the idea that activated vitamin D may be of help to some breast cancer patients:
In a preliminary trial, activated vitamin D was applied topically to the breast, once per day for six weeks, in 19 patients with breast cancer. Of the 14 patients who completed the trial, three showed a large reduction in tumour size, and one showed a minor improvement. Those who responded had tumours that contained receptors for activated vitamin D. However, other preliminary reports have not found that high levels of these receptors consistently correlate with a better outcome.
With a doctor’s prescription, compounding pharmacists can put activated vitamin D, a hormone, into a topical ointment. Due to potential toxicity, use of this hormone, even topically, requires careful monitoring by a physician. Standard vitamin D supplements are unlikely to duplicate the effects of activated vitamin D in women with breast cancer. The patients in the breast cancer trial all had locally advanced disease.
Melatonin
Melatonin has been reported to have anticancer activity against breast cancer cells in most though not all test tube studies. In a prelimi