By, Robert A. Wascher, MD, FACS
The information in this column is intended for informational purposes only, and does not constitute medical advice or recommendations by the author. Please consult with your physician before making any lifestyle or medication changes, or if you have any other concerns regarding your health.
DIET, SOY & BREAST CANCER RISK
Last week’s column reviewed new clinical research findings suggesting that higher levels of soy-derived isoflavones in the diet, and in the blood, may significantly reduce the risk of prostate cancer. This week, I will be discussing a new research study that makes similar claims regarding the prevention of breast cancer.
Breast cancer in women is, in several important ways, analogous to prostate cancer in men. Like prostate cancer, most breast cancer cells are fuelled by the body’s sex hormones (androgens stimulate prostate cancer growth, while estrogen in women stimulates breast cancer growth). Prostate cancer is the number one cause of cancer in men, and breast cancer is the number one cause of cancer in men. Approximately 192,000 cases of each of these cancers will be diagnosed in 2009, with prostate cancer accounting for about one-fourth of all cancers afflicting men, while breast cancer also represents about one-fourth of all cancers that affect women. Prostate cancer is the second most common cause of cancer death in men, and, analogously, breast cancer is the number two cause of cancer death in women. More than 27,000 men will die of prostate cancer in 2009, while more than 40,000 women will succumb to breast cancer this year.
In last week’s column (Diet & Prostate Cancer Risk), I reviewed an innovative clinical research study that assessed both the dietary intake of soy-derived isoflavones and the concentration of these dietary nutrients in the blood. Isoflavones belong to a larger group of dietary compounds that are, collectively, referred to as phytoestrogens, as these nutrients are able to stimulate (albeit weakly) chemical receptors for the sex hormone estrogen. In a newly published clinical study, in the American Journal of Clinical Nutrition, the results of a large prospective Chinese women’s health study add to previous similar research in suggesting that a diet rich in soybean-derived products, especially when consumed before and during adolescence, may be associated with a decreased overall risk of developing breast cancer later in life.
In this prospective public health study, more than 73,000 Chinese adolescent girls and women were followed for an average of 7.4 years. All of the participants in this very large study completed validated dietary surveys, and the incidence of new breast cancers among this very large group of Chinese women was then compared to their self-reported intake of soy-based foods.
The results of this study were rather striking, and were highly statistically significant when comparing the incidence of breast cancer among women with the highest levels of soy intake versus the women with the least soy intake. In this epidemiological study, the women who reported the highest regular dietary intake of soy-based foods were, overall, nearly 60 percent less likely to be diagnosed with premenopausal breast cancer during the course of this clinical research trial. This dramatic reduction in the risk of premenopausal breast cancer was observed in both the women who reported high levels of soy-derived foods in their diet and in the women who frequently consumed foods that were generally rich in isoflavones.
While this particular study did not measure isoflavone levels in the blood, as was done in the prostate cancer study that I reviewed last week, its results, nonetheless, mirror the findings of other similar epidemiological studies.
As with all survey-based disease prevention studies, of course, there is the potential for significant bias in this particular research study, and studies such as these cannot, by themselves, prove a “cause-and-effect” mechanism behind the clinical findings that they reveal. However, such studies, when conducted prospectively and with a high degree of scientific integrity, can still suggest potentially important disease prevention strategies. When the results of studies such as these appear to be especially compelling, they should then be followed-up by large, prospective randomized, placebo-controlled clinical research studies that provide so-called “Level I” clinical evidence.
Previous studies that have supported a role for soy consumption in breast cancer prevention have suggested that the increased consumption of soy-derived isoflavones before and around the time of adolescence is critically important, when the female breast is actively developing, and that this apparent protective effect of soy foods against breast cancer diminishes greatly after breast development is completed in early adulthood. (At the same time, however, the weakly estrogenic effects of dietary isoflavones have raised concerns about soy intake among women with a prior history of breast cancer, although there is no convincing scientific data, yet, showing that dietary isoflavones increase the risk of breast cancer recurrence.)
Another caveat that must be mentioned regarding the findings of this particular study is that the potentially beneficial effects of soy-derived foods, and of dietary isoflavones in general, in preventing breast cancer were observed in a homogeneous population of Asian women. Even if high levels of isoflavones in the diet really are protective against breast cancer, as this epidemiological study strongly suggests, it is still unclear whether or not this putative cancer prevention benefit applies equally to non-Asian women as well. Once again, only well-balanced, prospective, randomized, placebo-controlled clinical studies can confirm or contradict the findings of this very large Chinese public health study. Fortunately, there are several such studies underway at this time.
I will have much more to say, of course, regarding diet and breast cancer prevention, as well as many other evidence-based lifestyle and dietary strategies to reduce your risk of developing all of the top ten cancer killers, in my forthcoming book, “A Cancer Prevention Guide for the Human Race,” which is expected to be available in the spring of 2010.
Finally, although I don’t, as a rule, include links to other websites within this column, I am making an exception for The Prostate Cancer Charity in the United Kingdom. This cancer awareness charity is competing in an online contest to have their prostate cancer public service announcement displayed on London buses at no charge. Please click the following link, and cast your online vote for this charity’s worthy cause (you can cast a vote for them on a daily basis):
Bluefrog – The Prostate Cancer Charity
Disclaimer: As always, my advice to readers is to seek the advice of your physician before making any significant changes in medications, diet, or level of physical activity
Dr. Wascher is an oncologic surgeon, a professor of surgery, a widely published author, and a Surgical Oncologist at the Kaiser Permanente healthcare system in Orange County, California
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Robert A. Wascher, MD, FACS
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Dr. Wascher’s Archives:
5-24-2009: Diabetes, Glucose Control & Death
5-17-2009: Drug Company Marketing & Physician Prescribing Bias
5-10-2009: Hemorrhoids & Surgery
5-3-2009: Statin Drugs & Blood Clots (Thromboembolism)
4-26-2009: Are We Really Losing the War on Cancer?
4-19-2009: Exercise in Middle Age & Risk of Death
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4-5-2009: Does PSA Testing for Prostate Cancer Save Lives?
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3-15-2009: Depression, Stress, Anger & Heart Disease
3-8-2009: Coronary Artery Disease: CABG vs. Stents?; Swimming Lessons & Drowning Risk in Children
3-1-2009: Aspirin & Colorectal Cancer Prevention; Fish Oil & Respiratory Infections in Children
2-22-2009: Health Differences Between Americans & Europeans; Lycopene & Prostate Cancer
2-15-2009: Statin Drugs & Death Rates; Physical Activity, Breast Cancer & Sex Hormones
2-8-2009: Hormone Replacement Therapy (HRT) & Breast Cancer; Stool DNA Testing & Cancer of the Colon & Rectum
2-1-2009: Obesity and the Complications of Diverticulosis (Diverticulitis & Bleeding); Obesity, Weight Loss & Urinary Incontinence
1-25-2009: Prostate Cancer, Fatigue & Exercise; Does your Surgeon “Warm-up” Before Surgery?
1-18-2009: Cancer and Vitamins; Teenagers, MySpace and Risky Behaviors
1-11-2009: Exercise Reverses Some Effects of Fatty Meals; Vitamin C and Blood Pressure
1-4-2009: Secondhand Smoke & Heart Attack Risk; Poor Physical Fitness During Childhood & Heart Disease Risk During Adulthood
12-28-2008: Stress & Your Risk of Heart Attack; Vitamin D & the Prevention of Colon & Rectal Polyps
12-21-2008: Breast Cancer Incidence & Hormone Replacement Therapy; Circumcision & the Risk of HPV & HIV Infection
12-14-2008: Vitamin E, Vitamin C and Selenium Do Not Prevent Cancer; Postscript: A Possible Cure for Down’s Syndrome
12-7-2008: Generic vs. Brand-Name Drugs, Stress & Breast Cancer Survival
11-30-2008: A Possible Cure for Down’s Syndrome?; Smoking & Cognitive Decline; Calcium & Vitamin D & Breast Cancer Risk
11-23-2008: Breast Cancer & Fish Oil; Lymphedema after Breast Cancer Treatment; Vasectomy & Prostate Cancer Risk
11-16-2008: Vitamin E & Vitamin C: No Impact on Cardiovascular Disease Risk; Does Lack of Sleep Increase Stroke & Heart Attack Risk in Hypertensive Patients?
11-9-2008: Statins Cut Heart Attack Risk Even with Normal Cholesterol Levels; Statins & PSA Level
11-2-2008: Radiation Treatment of Prostate Cancer & Second Cancers; Sexual Content on TV & Teen Pregnancy Risk
10-26-2008: Smoking & Quality of Life
10-19-2008: Agent Orange & Prostate Cancer
10-12-2008: Pomegranate Juice & Prostate Cancer
10-5-2008: Central Obesity & Dementia; Diet, Vitamin D, Calcium, & Colon Cancer
9-28-2008: Publication & Citation Bias in Favor of Industry-Funded Research?
9-21-2008: Does Tylenol® (Acetaminophen) Cause Asthma?
9-14-208: Arthroscopic Knee Surgery- No Better than Placebo?; A Healthy Lifestyle Prevents Stroke
8-23-2008: Alcohol Abuse Before & After Military Deployment; Running & Age; Running & Your Testicles
8-12-2008: Green Tea & Diabetes; Breastfeeding & Adult Cholesterol Levels; Fish Oil & Senile Macular Degeneration
8-3-2008: Exercise & Weight Loss; Green Tea, Folic Acid & Breast Cancer Risk; Foreign Language Interpreters & ICU Patients
7-26-2008: Viagra & Sexual Function in Women; Patient-Reported Adverse Hospital Events; Curcumin & Pancreatic Cancer
7-13-2008: Erectile Dysfunction & Frequency of Sex; Muscle Strength & Mortality in Men; Cryoablation for Prostate Cancer
7-6-2008: Sleep, Melatonin & Breast Cancer Risk; Mediterranean Diet & Cancer Risk; New Treatment for Varicose Veins
6-29-2008: Bone Marrow Stem Cells & Liver Failure; Vitamin D & Colorectal Cancer Survival; Green Tea & Colorectal Cancer
6-22-2008: Obesity, Lifestyle & Heart Disease; Effects of Lifestyle & Nutrition on Prostate Cancer; Ginkgo Biloba, Ulcerative Colitis & Colorectal Cancer
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5-25-2008: Early Childhood Screening Predicts Later Behavioral Problems; Psychiatric Disorders Among Parents of Autistic Children; Social & Psychiatric Profiles of Young Adults Born Prematurely
5-18-2008: Can Statins Reverse Coronary Artery Disease?; Does Breast Ultrasound Improve Breast Cancer Detection?; Preventive Care Services at Veterans Administration (VA) Medical Centers
5-11-2008: Smoking Cessation & Risk of Death; Childhood Traumas & Adult Suicide Risk; “White Coat Hypertension” & Risk of Cardiovascular Disease
5-4-2008: Super-Size Me: Fast Food’s Effects on Your Liver; Exercise, Weight & Coronary Artery Disease; Contamination of Surgical Instruments in the Operating Room
4-27-2008: Stents vs. Bypass Surgery for Coronary Artery Disease; The “DASH” Hypertension Diet & Cardiovascular Disease Prevention; Testosterone Therapy for Women with Decreased Sexual Desire & Function
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4-13-2008: Breast Cancer Recurrence & Hormone Replacement Therapy (HRT); Carotid Artery Disease: Surgery vs. Stents?; Statin Drugs & Cancer Prevention
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3-23-2008: Age of Transfused Blood & Risk of Complications after Surgery; Obesity, Blood Pressure & Heart Size in Children
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3-2-2008: Medication & Risk of Death After Heart Attack; Hormone Replacement Therapy (HRT) & Mammogram Results; Selenium: Cancer, Heart Disease & Death
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2-17-2008: Exceptional Longevity in Men; Testosterone & Risk of Prostate Cancer; Smoking & Pre-malignant Colorectal Polyps
2-10-2008: Thrombus Aspiration from Coronary Arteries; Intensive Management of Diabetes & Death; Possible Cure for Down’s Syndrome?
2-3-2008: Vitamin D & Cardiovascular Health; Vitamin D & Breast Cancer; Green Tea & Colorectal Cancer
1-27-2008: Colorectal Cancer, Esophageal Cancer & Pancreatic Cancer: Update from the 2008 American Society of Clinical Oncology’s Gastrointestinal Cancers Symposium
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1-7-2008: Testosterone Supplements in Elderly Men; Colorectal Cancer– Reasons for Poor Compliance with Screening Recommendations
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