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SOY, CURCUMIN & PROSTATE CANCER RISK

Because chronic inflammation within the prostate gland is through to be an important risk factor for prostate cancer, anti-inflammatory dietary supplements and medications may be able to reduce the risk of prostate cancer by reducing inflammation.

Isoflavones from soy-based foods are known to act as a weak form of estrogen (the dominant female sex hormone).  Based upon this estrogen-like behavior, as well as potential anti-inflammatory properties, soy isoflavones are being studied as possible prevention and treatment agents for prostate cancer, and other types of cancer. 

Curcumin, which is present in the Indian curry spice turmeric, is also known to have potent anti-inflammatory properties, and has also been the subject of considerable cancer prevention and cancer treatment research.

A newly published prospective, randomized, blinded, placebo-controlled research study, published in the current issue of the journal Prostate, suggests that the combination of soy isoflavones and curcumin may have important potential prostate cancer prevention properties.

In the first part of this study, human prostate cancer cells were treated with a combination of soy isoflavones and curcumin.  Treatment of these human cancer cells with soy isoflavones and curcumin resulted in a significant reduction of prostate-specific antigen (PSA) production by these malignant cells (PSA is a marker of both prostate gland inflammation and prostate gland cancer).

As regular readers of this column are already aware, treatments performed in the laboratory that have beneficial effects on cancer cells, or on mice or rats, do not always have the same positive effects on living, breathing human beings.  Therefore, the findings of the second part of this study are of particular interest.  A total of 85 men with elevated PSA levels, but without prostate cancer (as confirmed by prostate biopsy), were enrolled in the second phase of this intriguing small study.  These 85 men were divided into two groups, and one group received daily supplements containing both soy isoflavones and curcumin, while the second (control) group of men received placebo (sugar) pills that were identical in appearance to the supplement pills (neither the 85 men, nor the nurses who dispensed the supplement pills and placebo pills, were aware of which pills each study volunteer was receiving until after the research study had been completed).

PSA blood levels were tested at the beginning of the clinical portion of this study, and once again 6 months later.  As was observed in the prostate cancer cells during the first part of this study, men with a PSA level of 10, or higher, experienced a significant reduction in their blood PSA levels 6 months after starting daily supplementation with soy isoflavones and curcumin.

Although this brief study cannot definitively confirm that soy isoflavone and curcumin supplements reduce the risk of prostate cancer, their ability to reduce elevated PSA levels in men with chronic prostate inflammation, but without evidence of prostate cancer, at least suggests a potential role in the prevention of prostate cancer (presumably through a reduction in prostate gland inflammation).

While there are multiple human research studies underway that are evaluating the effectiveness of soy isoflavones as cancer prevention agents, currently, there are no major human studies looking at the effects of curcumin on prostate cancer risk.  Based upon the findings of this small, interesting study of soy isoflavones and curcumin, which suggest a potential additive effect on PSA reduction when both of these dietary supplements are taken together, human research trials should be developed to look at the long-term impact, if any, of combined soy isoflavone and curcumin supplementation on prostate cancer risk.

For additional research information on soy isoflavones and curcumin in cancer prevention and cancer treatment, please review the following previous columns:

Soy Foods & Stomach Cancer Risk

Cruciferous Vegetables, Soy & Breast Cancer Risk

Soy Isoflavones & Recurrent Prostate Cancer

Soy Isoflavones Decrease Breast Cancer Recurrence Risk

Genistein (Soy Isoflavone) & Prostate Cancer

Diet, Soy & Breast Cancer Risk

Viagra & Sexual Function in Women; Patient-Reported Adverse Hospital Events; Curcumin & Pancreatic Cancer

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 cancer researcher, an oncology consultant, and a widely published author  

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Welcome to Weekly Health Update

“A critical weekly review of important new research findings for health-conscious readers”

SOY ISOFLAVONES REDUCE BREAST CANCER

RECURRENCE RISK

Regular readers of this column are already aware of the controversy surrounding soy isoflavone intake and breast cancer risk.  As happens frequently in clinical research (unfortunately), contradictory research findings have made it difficult to understand the true relationship between dietary soy intake and breast cancer risk (if one exists).  There is, for example, both laboratory and clinical data suggesting that a diet rich in soybean-derived products may be associated with a lower risk of developing breast cancer.  At the same time, because genistein and other dietary isoflavones are known to weakly mimic the effects of estrogen, there has been some concern that a diet rich in isoflavone “phytoestrogens” may increase both the risk of developing a new breast cancer and the risk of developing a recurrence of a previous breast cancer.  (In fact, there is data from laboratory research studies showing that genistein can indeed fuel the growth of human breast cancer cells growing in culture dishes, when exposed to high concentrations of this soy-derived isoflavone.)

A growing body of public health research, primarily from Asian countries where tofu and other soy-based foods are frequently consumed, appears to link increased soy consumption with a decreased lifetime breast cancer risk, particularly when soy-based foods are consumed during adolescence, during the time when development of the female breast is most active (Soy & Breast Cancer Risk).  (Interestingly, there is also recent research suggesting that soy products might also reduce the risk of prostate cancer, which is another hormonally driven cancer:   Genistein & Prostate Cancer Cells, Dietary Soy & Prostate Cancer Risk.)

Although epidemiological research is, increasingly, suggesting that a diet rich in soybean-derived foods might lower a woman’s lifetime risk of developing breast cancer, many breast cancer experts have remained apprehensive regarding dietary isoflavone intake in women with a prior history of breast cancer, in view of the estrogen-like effects of these “phytoestrogens.”  As I have already noted, there is considerable research data available to suggest that soy-derived isoflavones can, at least under certain laboratory conditions, stimulate estrogen-sensitive breast cancer cells to grow and divide.  These research findings have left many oncologists feeling uncomfortable in recommending soy-based foods to their breast cancer patients.  Now, a newly publish public health study in the Journal of the American Medical Association suggests that soy-based foods may actually reduce the risk of breast cancer recurrence, and death due to any cause, in women who have previously been diagnosed with this very common form of cancer.

In this study, which was performed in Shanghai, China, 5,042 female breast cancer survivors (ages 20 to 75 years) were followed for an average of almost 4 years.  All of these patient volunteers underwent detailed surveys regarding their lifestyle habits, including their diets.  These patients, who were originally diagnosed with breast cancer between 2002 and 2006, were surveyed at 6, 18, 36 and 60 months following their original diagnosis with breast cancer.  

The results of this study indicate that the breast cancer survivors who consumed the greatest amount of soy-based foods in their daily diets were 32 percent less likely to experience a recurrence of their breast cancer when compared to the women who consumed the least amount of soy-based isoflavones.  Moreover, the women who consumed the greatest amount of soy were also 29 percent less likely to die, from any cause, when compared to the women who consumed the least amount of soy-derived foods.

A particularly interesting and unexpected finding of this study was that both women with estrogen sensitive breast cancers and women with tumors that were not sensitive to estrogen appeared to experience a significantly decreased risk of breast cancer recurrence if they frequently consumed soy products.  Another important finding of this study was that women who were taking the estrogen-blocking cancer treatment drug tamoxifen also appeared to enjoy a reduced risk of breast cancer recurrence with higher levels of dietary soy intake.  Additionally, the researchers noted that high levels of soy intake appeared to be about as effective in reducing the risk of breast cancer recurrence as the breast cancer prevention drug tamoxifen, alone.

The results of this very important study mirror the findings of the only other prospective clinical study that has looked at the impact of soy-based foods on breast cancer recurrence (the “Life After Cancer Epidemiology,” or “LACE,” study).  The LACE study, which was performed in the United States, followed nearly 2,000 breast cancer survivors for, on average, more than 6 years.  In the LACE study, women who were taking tamoxifen, and who also consumed the highest amount of soy-based dietary isoflavones, were 50 percent less likely to develop a recurrence of their breast cancer when compared to women who reported the lowest consumption of soy-derived foods.

As I have pointed out previously, epidemiological research studies based upon dietary surveys are susceptible to several types of bias which, in turn, can cause researchers to draw the wrong conclusions.  In this case, however, there are now two large prospective cohort studies that have reached essentially the same conclusions (albeit with a rather limited duration of patient follow-up).  Both studies strongly suggest that high levels of soy-based isoflavones in the diet may be able to significantly reduce the risk of breast cancer recurrence.  Based upon the findings of this large Chinese study, the apparent cancer risk reduction effect associated with high levels of soy intake also appears to benefit premenopausal and postmenopausal women, as well as women who are taking the estrogen-blocking drug tamoxifen, women with estrogen-sensitive tumors, and women with (counter-intuitively) estrogen-resistant tumors.

In view of the limited duration of patient follow-up in both of these clinical breast cancer studies, as well as the limitations of survey-based epidemiological research in general, I would like to see updated data from both of these studies after at least 10 years of patient observation before I would be willing to tell my breast cancer patients that they should significantly increase their dietary soy intake.  On the other hand, the rather compelling data presented by both of these clinical research studies will also make me less anxious when any of my breast cancer patients decide, of their own accord, to increase their intake of soy-derived isoflavones.

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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