The Buzz on Nutrition:
Could breast cancer risk or disease recurrence be affected by nutritional factors?
We have all heard that diet affects our risk of the development of heart disease and diabetes. However, how might diet affect our risk of breast cancer, or the risk of breast cancer recurrence? This review serves as a short summary of the current scientific data on diet, alcohol, and supplements on breast cancer risk and recurrence.
Could Dietary Modifications Decrease the Risk of Breast Cancer?
Evidence for an association between fruit and vegetable intake and breast cancer risk remains somewhat debated. A 2011 study published in the American Journal of Epidemiology evaluated the DASH diet (which was initially touted for decreasing complications of hypertension and heart disease), and the risk of the development of postmenopausal breast cancer. Components of the DASH diet include eating increased amounts of fruit and vegetables, while having little red meat, and limiting salt and processed carbohydrates. This study found that consuming specifically the 4-5 servings daily of fruits and vegetables might lower the odds of developing ER negative breast cancer, but no risk reduction was found for ER positive breast cancer. Another study published in 2012 in the Journal of Breast Cancer Research and Treatment found that there was a small reduction in the risk of breast cancer in women who consumed diets with high levels of fruits or fruits and vegetables. There was no noted reduction in women who consumed diets high in vegetables only. These newer studies are encouraging, as they contradict a 2001 study that demonstrated no breast cancer risk reduction from fruit and vegetable consumption.
A study conducted at Harvard and published in the Journal of the National Cancer Institute in December 2012 found that women who have higher levels of circulating carotenoids have a lower risk of breast cancer. Carotenoids are micronutrients found in fruits and vegetables, and include alpha-carotene, beta-carotene, lutein+zeaxanthin, and lycopene. The researchers found that women who had higher levels of these carotenoids had lower risks of breast cancer. The biggest risk reduction for ER negative breast cancers, but there was still risk reduction for ER positive breast cancers. Carotenoids are found in high concentrations in dark leafy greens, carrots, sweet potatoes, and tomatoes.
Could Dietary Modifications Decrease the Risk of Breast Cancer?
A study published in 2012 in the American Journal of Clinical Nutrition found that for every 10 grams of added daily fiber, breast cancer risk decreased by 7%. The findings are based on a metaanalysis of 10 studies involving more than 712,000 women. Women who were at the top percentile of fiber consumption had an 11% lower risk of breast cancer than women at the bottom percentile of fiber consumption. The recommended daily amount of fiber consumption for women is 25 grams, but most women take in less than 15 grams daily.
High Fat Dairy:
A study published in 2013 in the Journal of the National Cancer institute reviewed nearly 1900 breast cancer survivors and their risk of recurrence with a high fat diet. The researchers found a higher risk of breast cancer recurrence, breast cancer mortality, and all-cause mortality in those women who consumed a high dairy-fat diet. There was no difference in recurrence for women consuming a low dairy-fat diet. High dairy fats are found in ice cream, hard cheese, pudding, and whole milk.
Studies seem conflicted about the benefits of this diet on breast cancer risk. The cornerstone of the Mediterranean diet is the consumption of olive oil, legumes, fruits, vegetables, fish, and red wine, with only moderate consumption of meat. A 2010 study of nearly 15,000 women in the American Journal of Clinical Nutrition found a marginal benefit to this diet in only post-menopausal women. A 2013 study of over 49,000 Swedish women did not note a lower risk of breast cancer in either pre or postmenopausal women.
Soy: The Pendulum Swings
Soybeans are legumes that contain relatively high concentrations of isoflavones. These are a type of phytoestrogen, a compound chemically similar to in appearance to estrogen. Initially, phytoestrogens found in soy products were thought to increase the risk of breast cancer tumor growth, and a 2001 pharmacy review actually suggested that women with breast cancer should be cautious about soy consumption. Many of the early studies evaluating the risk of breast cancer due to soy were completed on rats in the lab, not on humans. The pendulum started to swing in 2006, when a review suggested the opposite of previously believed- that soy could actually decrease the risk of breast cancer. A metaanalysis of 14 studies published on the topic in 2011 found that soy consumption did indeed decrease the risk of breast cancer recurrence, but this was unfortunately noted only in Asian populations, not Western populations. An even more recent study of nearly 9000 hormone positive breast cancer survivors from both the US and China found that women who consumed 10 mg/day of soy had a 25% lower risk of recurrence!
How is it possible that soy might actually DECREASE breast cancer risk? The isoflavones found in soy have been found to have both estrogen and anti-estrogen effects. Isoflavones can block the body’s real circulating estrogen from binding to estrogen receptors. Estrogen in the body is much more potent than isoflavones, so blocking the receptors is beneficial. Isoflavones also stop the formation of estrogens in fat tissue, and stimulate production of a protein that binds up estrogen in the blood, making it unavailable to bind to the estrogen receptor. Isoflavones also have anti-oxidant and anti-inflammatory properties to reduce cancer growth.
So what’s the bottom line?
Soy in moderate dietary amounts is safe, and in human studies, does not appear to increase breast cancer risk. Dietary soy consumption might actually decrease breast cancer risk in certain patient populations. However, non-dietary soy supplements are still not currently recommended until stronger scientific data is available.
A 2002 metaanlysis from England reviewed 53 studies involving nearly 60,000 women on the effects of alcohol consumption and the risk of breast cancer. This study suggested that approximately 4% of breast cancer cases could be attributable to alcohol consumption. Each additional drink per day increased a woman’s risk by 7%. A 2013 study published by the NCI demonstrated that young women drinking alcohol (6 drinks/week) prior to their first pregnancy had increased risks of breast cancer, especially for women becoming pregnant later in life. A study specifically looking at mortality from breast cancer did not demonstrate that drinking alcohol increased mortality from breast cancer once diagnosed, unless consumption was more 2 drinks/day. A study in the 2013 International Journal of Cancer demonstrated that these increased risks of breast cancer related to high alcohol consumption held true across African American, Japanese, and Latino populations. Lastly, a 2013 review in the Annals of Oncology demonstrated that even light drinking increased the risk of breast cancer, and that alcohol was estimated to be responsible for 5000 new cases yearly.
Unfortunately for women, the effects of even light alcohol consumption on increasing breast cancer risk must be weighed very closely with the potential small benefits on cardiovascular health.
Supplements and Green Tea
Many investigators have looked at supplements and breast cancer risk. The VITAL study, published in 2010, queried over 35,000 women on their supplement use, and then compared this to their development of breast cancer. The only supplement associated with reduced breast cancer risk was the use of fish oil. There was no reduced breast cancer risk with the use of common supplements such as glucosamine, acidophilus, Coenzyme Q10, garlic, black cohash, ginkgo, ginseng, melatonin, and St. John’s wort. A provocative study out of Norway was published in 2009. At that time, Norway did not have mandatory folic acid fortification of flour and grain products like the US did. This study demonstrated that folic acid plus Vitamin B12 supplementation might actually increase all cancer mortality. There are other studies also that suggest high doses of folic acid may enhance growth of cancer cells. In contrast, some epidemiologic studies suggest folate supplementation may decrease breast cancer risk in women who have moderate or high alcohol consumption.
A 2010 metaanylsis published in the Journal of Breast Cancer Research and Treatment revealed that consumption of more than 3 cups daily of green tea was associated with lower breast cancer recurrences.
Hormone Related Supplements
Many women take herbal supplements to relieve menopausal symptoms. Data on black cohosh remains inconsistent for menopausal relief, and its effect on breast cancer risk remains unclear. A 2008 study on mice demonstrated black cohosh increased the risk of breast cancer metastasis in the mice. However, a review published in 2007 in the International Journal of Cancer surveyed nearly 1000 breast cancer patients on their use of hormone-related supplements for menopause prior to their cancer diagnosis. Black cohosh, ginseng, red clover were studied. Black cohosh seemed to have a small protective effect, with seemingly antiestrogenic, antioxidant, and antiproliferative effects. The benefit of black cohosh was unfortunately not demonstrated in the more recent VITAL study from 2010.