Zinc, omega-3 fatty acids, and prostate cancer survival

A study in Sweden examined the effects of zinc and the omega-3 fatty acid DHA on mortality in prostate cancer patients. Five-hundred twenty-five men with prostate cancer were followed for twenty years after being diagnosed with prostate cancer.  Baseline dietary habits, stage of cancer at diagnosis, and deaths over the twenty years were recorded and analyzed.1

The authors chose to investigate these two nutrients because zinc and omega-3s share the common action of attenuating the inflammatory response, and chronic systemic inflammation may fuel prostate cancer progression. Importantly, zinc and DHA are both difficult to obtain on a plant-based diet.

Zinc is especially concentrated in the prostate, but zinc levels become depleted in cancerous cells. Addition of zinc to cultured prostate cancer cells leads to cell death, possibly by suppressing the activity of inflammatory molecules. A previous study found that long-term zinc supplementation was associated with reduced risk of advanced prostate cancer.2

The researchers organized the study participants into quartiles according to their intakes of zinc and DHA. In men who were diagnosed with early stage cancers, the highest quartile of zinc intake (15.7 mg zinc daily or more) was associated with a 74% reduction in risk of death from prostate cancer compared to the lowest quartile (12.8 mg zinc daily or less). Absorption of zinc tends to be low on a vegan diet – beans, whole grains, nuts, and seeds have high zinc content, however these foods also contain substances that inhibit the aborption of zinc.3 A 2009 study of vegetarians found a high prevalence of zinc deficiency.4 To correct for bioavailability, the zinc requirement for vegans may be as much as 50% higher than that of omnivores.5

I recommend zinc supplementation with a multivitamin and mineral to ensure sufficient zinc intake in vegans or those who minimize animal foods.

The connection between omega-3 intake and prostate cancer is somewhat complex. For example, flaxseed oil was found to increase prostate cancer risk, whereas whole flaxseed, EPA, and DHA were found to be protective.6,7,8 EPA and DHA are known to have anti-cancer and anti-inflammatory properties.9 In this study, the highest quartile of DHA intake was associated with 30% reduced risk of overall prostate cancer mortality, and a 45% risk reduction in men diagnosed at early stages, supporting the idea that DHA is protective against prostate cancer. Plant foods contain ALA, which can be elongated to DHA, but the major food source of DHA is fish, which often contains pollutants and is not acceptable for vegetarians and vegans. For these reasons, I recommend a laboratory cultivated DHA supplement made from micro-algae, which is also a more environmentally sustainable option than fish or fish oil.



1. Meyer MS, Kasperzyk JL, Andren O, et al. Anti-inflammatory nutrients and prostate cancer survival in the Örebro Prostate Cancer Survivors Cohort. [Abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; 2010. Abstract nr 5747

MedPageToday. AACR: Zinc Linked to Prostate Cancer Survival. http://www.medpagetoday.com/MeetingCoverage/AACR/19685

2. Gonzalez A, Peters U, Lampe JW, White E. Zinc intake from supplements and diet and prostate cancer. Nutr Cancer. 2009;61(2):206-15.

3. Hunt JR. Bioavailability of iron, zinc, and other trace minerals from vegetarian diets. Am J Clin Nutr 2003;78(suppl):633S–9S.

4. de Bortoli MC, Cozzolino SM. Zinc and selenium nutritional status in vegetarians. Biol Trace Elem Res. 2009 Mar;127(3):228-33.

5. Frassinetti S, Bronzetti G, Caltavuturo L, et al. The role of zinc in life: a review. J Environ Pathol Toxicol Oncol. 2006;25(3):597-610.

6. Brouwer IA, Katan MB, Zock PL. Dietary alpha-linolenic acid is associated with reduced risk of fatal coronary heart disease, but increased prostate cancer risk: a meta-analysis. J Nutr 2004 Apr;134(4):919-22

7. Demark-Wahnefried W, Polascik TJ, George SL, et al. Flaxseed supplementation (not dietary fat restriction) reduces prostate cancer proliferation rates in men presurgery. Cancer Epidemiol Biomarkers Prev. 2008 Dec;17(12):3577-87.

8. Leitzmann MF, Stampfer MJ, Michaud DS, et al. Dietary intake of n-3 and n-6 fatty acids and the risk of prostate cancer. Am J Clin Nutr. 2004 Jul;80(1):204-16.

9. Spencer L, Mann C, Metcalfe M, et al. The effect of omega-3 FAs on tumour angiogenesis and their therapeutic potential. Eur J Cancer. 2009 Aug;45(12):2077-86. 

Eggs and poultry with skin double prostate cancer recurrence risk

Approximately 1300 men who had been diagnosed with prostate cancer were followed for two years to document their dietary patterns and recurrence or progression of their disease. In this study, two specific animal foods were found to be risky - the men that ate the most eggs or poultry with skin were twice as likely to have their disease recur or progress.1

This study makes three important points.

  1. Diet does matter, even after a prostate cancer diagnosis.
  2. There is something in chicken, specifically in the crispy outer portion and skin that is powerfully cancer-inducing. Heterocyclic amines, carcinogenic compounds that are formed when meat is cooked at high temperatures, are a probable culprit. A November 2009 study of 175,000 men showed an increase in prostate cancer risk with consumption of barbequed and grilled meat.2
  3. Consumption of eggs and egg whites is not without risk. Eggs are high in animal protein, which has been linked to cancers. Our populations’ idea that more protein is favorable and that egg (whites) are the perfect food does not hold up to scrutiny. Eggs also could affect prostate cancer due to their high choline content – egg consumption increases the amount of choline in the plasma, and high plasma choline increases prostate cancer risk.3 

Four previous studies implementing a plant-based diet and exercise following prostate cancer diagnosis found a decrease in prostate cancer progression rates.4 

Dietary strategy for prostate health 

 

References:

1. Richman EL et al. Intakes of meat, fish, poultry, and eggs and risk of prostate cancer progression. Am J Clin Nutr. 2009 Dec 30. [Epub ahead of print]

2. Sinha R et al. Meat and meat-related compounds and risk of prostate cancer in a large prospective cohort study in the United States. Am J Epidemiol. 2009 Nov 1;170(9):1165-77. Epub 2009 Oct 6.

3. http://www.foodnavigator.com/Science-Nutrition/Meat-not-linked-to-prostate-cancer-recurrence-risk

4. R. W.-L. Ma, K. Chapman. A systematic review of the effect of diet in prostate cancer prevention and treatment. J Hum Nutr Diet, 22, pp. 187–199