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Prostate Cancer

Prostate Cancer—What we All Must Know

  • Prostate cancer is the second most common cancer in men. There were an estimated 238,590 new diagnoses last year alone.
  • Ethnicity affects risk. Africans and African-Americans are most at risk while Asians have the lowest risk.
  • Ethnic risks have genetic relationships, yet there is a large focus on dietary influences on risk as well.
  • The recent study proclaiming that omega-3 fatty acids may increase prostate cancer risk has many weaknesses and shouldn’t deter patients from eating fish or consuming omega-3 supplements.
  • Zinc is an important mineral for prostate health.
  • Dairy products, more specifically whole milk, may increase the chances of getting prostate cancer.
  • Soy has several anti-prostate cancer benefits. However, it has its drawbacks, including the fact it is mostly a GMO (genetically modified organism) and is regularly treated with the herbicide glyphosate.

Prostate cancer is the second most common cancer (behind skin cancer) in American men. The American Cancer Society estimates that roughly 238,590 new cases were  diagnosed in 2013, and 29,720 men will die from this cancer.1

Other statistics show that prostate cancer risk increases with age, with 6 of every 10 cases diagnosed in men over the age of 65. Additionally, diagnosis is rare in men under 40. The average age of diagnosis is 67.

One in six men will be diagnosed with prostate cancer at some point in his life, and one in 36 will die from the disease. These statistics are important because the majority of men will not die from prostate cancer. There are more than 2.5 million men alive currently who have been diagnosed with the disease.

Sharp differences in prostate cancer risk exist among different ethnic groups. For example, Africans and African-Americans carry the greatest risk of prostate cancer, while Asians (Japanese, Chinese, Indian) have the lowest risk, according to genetic research.2

At the same time, because of these ethnic differences, much attention has been focused on cultural differences in diet as a possible cause of the observed prostate cancer risk. A striking example of this is when Japanese and Chinese men immigrate to the U.S., their risk of prostate cancer begins to approximate that of Caucasian Americans. Additionally, in Japan, prostate cancer incidence has increased with the adoption of Western diet and lifestyle.3

Do Omega-3s Cause Prostate Cancer?

Recently, the connection between prostate cancer and diet and dietary supplements have garnered even more attention with the recent headline-grabbing study “Plasma Phospholipid Fatty Acids and Prostate Cancer Risk in the SELECT Trial” published July 2013 in the Journal of the National Cancer Institute. This study suggested an association between elevated  omega-3 fatty acid levels and increased risk of prostate cancer.4

Despite the attention this study generated, it was readily scorned from a variety of sources and should be interpreted with a significant degree of caution for the following reasons:

  1. This was a retrospective, nested, case-controlled study, which means the researchers pulled data from a previously conducted study looking at other aspects of omega-3 oils and prostate cancer. In other words, they used data from a study that was not intended to examine omega-3 oil blood levels and risk of prostate cancer.
  2. The investigators never examined the study subjects’ dietary intake of omega-3 supplements or fish.
  3. Plasma omega-3 levels (used as the marker in the test) can vary significantly from day to day. The study conclusions are based on only one blood sample.  A subject who consumed fish the day of the test would have much higher levels than someone who did not. (A more accurate way to assess long-term levels of omega-3s is the omega-3 index, which measures both eicosapentaneoic acid (EPA) and docosahexanoeic acid (DHA) in red blood cells.)
  4. There are many confounding risk factors that can influence the likeliness of tumors in this study that may have influenced the outcome, such as:

– 80 percent of the subjects with cancer were obese or overweight.

– 64 percent of the subjects with cancer regularly consumed alcohol.

– 53 percent of the subjects with cancer were smokers.

– 30 percent of the subjects with cancer had at least one first-degree relative with prostate cancer.

  1. The investigators, as mentioned previously, did not track fish oil supplement or actual fish consumption in the study subjects. One possible cause for the study findings may  relate to how omega-3 fatty acids are extremely vulnerable to oxidative damage.
  2. Another possible cause for the study outcome may relate to the fact that many fish contain neurologically and developmentally toxic amounts of methylmercury, dioxins and polychlorinated biphenyls (PCBs).8

Overall, the outcome of this study is in stark contrast to other studies that were specifically designed to analyze dietary omega-3 intake and show a protective benefit against prostate cancer.9-10 Furthermore, when one considers the number of additional studies that display the anti-inflammatory effects of omega-3 fatty acids and the fact that study investigators did not suggest a credible biological mechanism, it is difficult to understand how omega-3 fatty acids led to increased prostate cancer in these subjects.

Lastly, the identification of one physiologic marker (elevated plasma omega-3 levels) that is easily influenced by diet and measured at only one point in time, in a group of subjects with a particular condition (prostate cancer) does not prove causation in any way.

Based on these weaknesses—not to mention the known, wide-ranging health benefits attributable to omega-3 fatty acids in many other studies—it would be unwise to suggest that patients discontinue eating fish or taking omega-3 supplements based on this study alone.

Additionally, the importance of adequate antioxidant consumption along with omega-3 (and other oils) cannot be understated. Brightly colored plant foods are rich in antioxidants and convey many additional health benefits. Patients taking omega-3s supplements should be encouraged to eat a diet rich in brightly colored plant foods such as berries, greens and cabbages, to name a few.

Omega-3 oils aren’t the only food ingredients that have a positive effect on prostate cancer. Here are some other nutrients that have been shown to be protective against this disease.

Zinc

Zinc is thought to have a protective effect against the development of prostate cancer.11 A healthy prostate gland concentrates higher amounts of zinc than any other area of the body, yet early on in prostate cancer these levels decline.12

Increasing zinc levels may protect against prostate cancer. However, accumulation of zinc in the prostate may be prevented by compromised zinc uptake transporters that may be present if tumor development has already started.13

Despite this, high cell levels of zinc are important for prostate health and may still inhibit prostate cancer development.14 Zinc-rich foods include oysters, beef, lamb, spinach, pumpkin and squash seeds, cashews, cocoa (and dark chocolate), pork, chicken, mung beans and mushrooms.

Soy

Soy has specific anti-cancer health benefits that are attributable to the presence of isoflavone, a plant nutrient found mostly in soy beans .15 The lower incidence of prostate cancer in Asian countries may be attributable to the native high-soy diets.16 The anti-prostate cancer effects of soy are nearly indisputable; there are several studies supporting this conclusion.17-19

Soy isoflavones inhibit prostate (and other) cancer growth by affecting processes in your cells, including apoptosis, inflammation, cellular proliferation and androgen receptor signaling.20

Other indirect effects include:22

  • Inhibition of alpha-5 reductase (converts testosterone into the more potent dihydrotestosterone).
  • By binding to androgen receptors, soy helps to block tumor growth.
  • Increases sex-hormone-binding globulin, which in turn binds to testosterone, limiting its availability to stimulate tumor growth.

While the protective effects of soy against prostate cancer are fairly well established, patients should be made aware that soy is also a widely distributed, genetically modified organism. In the United States, 85 percent of soy is genetically engineered, most of which is the Roundup Ready Soybean, which allows the soy plant to survive application of the herbicide Roundup (Glyphosate).

Health-conscious people may have concerns about GMO foods themselves, as well as soy in particular, that has had herbicide applied directly to it.

Is This the Real Culprit?

There is far more evidence to show dairy products may have a role to play in prostate cancer than there is to show omega-3s are to blame. While not strongly associated with prostate cancer development, there is evidence that dairy and high-calcium diets have a negative influence on prostate cancer.23 Dairy (milk) may increase prostate cancer risk through its estrogen content or by its calcium content, both of which have been associated with prostate cancer.24-25

A study looking more specifically at milk type found that 2.5 or more servings per day (compared to half a serving daily or less) was associated with increased prostate cancer incidence.26 In this study, whole milk consumption was associated with fatal prostate cancers, while low-fat milk consumption was associated with early stage, low-grade, screening-detected prostate cancer.

A separate study that analyzed milk intake on post-prostate cancer diagnosis found that total milk and dairy intake was not associated with a greater risk of prostate cancer death. However, subjects with the greatest intake of whole milk had an increased risk of disease progression compared to men who had high intakes of low-fat dairy.27

Conclusion

The recent study linking blood levels of omega-3 fatty acids to prostate cancer has several limitations. Of more importance are the several other studies that show a benefit of omega-3 on prostate health. Omega-3s should be consumed with plenty of antioxidants to limit their oxidation into unhealthy products.

Zinc is also important for healthy prostate cells and should be consumed as part of a plant-rich diet. Whole milk dairy products may carry a risk for increased prostate cancer, while soy can prevent and limit prostate cancer development

Action Steps

Prostate Health

We don’t know enough about omega-3 fatty acids, especially from the study published July 2013 in the Journal of the National Cancer Institute, to say you should stop eating fish or taking omega-3 supplements. Omega-3 fatty acids have shown to be of benefit in prostate cancer, not to mention many other areas of health. Forthose who are interested in protecting prostate health, these dietary factors are recommended:

• Omega-3 fatty acids shouldn’t be shunned based on the recent study. However, it is important that omega-3s should be consumed with plenty of antioxidants and be of the purest quality.

• If you have prostate concerns, try to limit dairy products, especially whole milk.

• Eat a diet rich in zinc, which is found in several animal products but even healthier sources include spinach, pumpkin and squash seeds, cashews, mung beans and mushrooms.

• Some people may want to consider soy isoflavones for their prostate health. However, you must be careful with soy because it is a GMO and may have been sprayed with the herbicide glyphosate.

• Supplemental forms of soy isoflavones may be a healthier way to get the benefits of soy.

 

 

References:

1. http://www.cancer.org/cancer/prostatecancer/detailedguide/prostate-cancer-key-statistics.

2. Zeigler-Johnson CM, et al. Hum Hered. 2002;54(1):13-21.

3. http://medicalcenter.osu.edu/patientcare/healthcare_services/prostate_health/prostate_cancer/risk_factors_prostate_cancer/Pages/index.aspx.

4. Brasky TM, et al. J Natl Cancer Inst. 2013 Aug 7;105(15):1132-41.

5. Farmer EE, et al. Curr Opin Plant Biol. 2007 Aug;10(4):380-6.

6. Moore K, et al.  Free Radic Res. 1998 Jun;28(6):659-71.

7.  Marnett LJ. Mutat Res. 1999 Mar 8;424(1-2):83-95.

8. Mozaffarian D, et al. JAMA. 2006 Oct 18;296(15):1885-99.

9. Torfadottir JE, et al. PLoS One. 2013;8(4):e59799.

10. Szymanski KM, et al.  Am J Clin Nutr. 2010 Nov;92(5):1223-33.

11. Park SY, et al. Prostate. 2013 Feb 15;73(3):261-6.

12. Costello LC, et al. Prostate. 1998 Jun 1;35(4):285-96.

13. Kolenko V, et al.  Nat Rev Urol. 2013 Apr;10(4):219-26.

14. Ho E, et al. Curr Opin Clin Nutr Metab Care. 2009 Nov;12(6):640-5.

15. Adjakly M, et al. Anticancer Res. 2013 Jan;33(1):39-44.

16. Dong X, et al. Food Chem. 2013 Dec 1;141(3):1923-33.

17. Chiyomaru T, et al. PLoS One. 2013 Aug 1;8(8):e70372.

18. Swami S, et al. Int J Cancer. 2009 May 1;124(9):2050-9.

19. Handayani R, et al. J Nutr. 2006 Jan;136(1):75-82.

20. Horie S. Korean J Urol. 2012 Oct;53(10):665-72.

21.  Zhou JR, et al. J Nutr. 1999 Sep;129(9):1628-35.

22. http://www.cedars-sinai.edu/Patients/Programs-and-Services/Urology-Academic-Practice/Patient-Guide/Soy-for-Prostate-Cancer.aspx.

23. Leitzmann MF, et al. Clin Epidemiol. 2012;4:1-11.

24. Tate PL, et al. Nutr Cancer. 2011 Nov;63(8):1361-6.

25.  Giovannucci E, et al. Cancer Epidemiol Biomarkers Prev. 2006 Feb;15(2):203-10.

26. Song Y, et al. J Nutr. 2013 Feb;143(2):189-96.

27. Pettersson A, et al. Cancer Epidemiol Biomarkers Prev. 2012 Mar;21(3):428-36.

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