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Research Newsletter-Spring/Summer 2007


Dietary influences on DNA integrity and prostate cancer prevention

Emily Ho, Ph.D.
Principal Investigator, Linus Pauling Institute;
Assistant Professor of Nutrition and Exercise Sciences, Oregon State University

Prostate cancer is the most common cancer in American men, accounting for 33% of male cancer cases in 2005. Factors influencing prostate cancer risk include age, race, family history, hormone levels, chronic inflammation, and diet. Of these factors, we may be able to influence inflammation, and we can definitely influence our diet. The U.S. has the highest rate of prostate cancer in the world, and Asian countries have the lowest. However, migration studies show that Asian men who have moved to the U.S. have a much higher rate of prostate cancer, suggesting that lifestyle factors, such as diet, play a significant role in development of prostate cancer (and not just genetics).

One significant dietary nutrient that is limited in the U.S. diet and that can affect prostate cancer risk is zinc. Zinc is vital for the functioning of over 300 enzymes and over 1000 proteins in the human body. The prostate contains the highest concentration of zinc of all soft tissues in males. Studies have shown that lower zinc intake is associated with increased rates of prostate cancer. Through our research, we have shown that zinc deficiency leads to greater oxidative stress, increased DNA damage, decreased DNA repair, and, thus, increased cancer risk.

We are also taking a whole-food approach to dietary cancer chemoprevention. Rather than using individual compounds extracted from foods, we are looking at the effect of whole foods, which provide a combination of nutrients and phytochemicals. This combination possibly provides more protection than one or two compounds alone. For example, a recent study with rats showed that whole tomato powder provided greater protection from death due to prostate cancer than just lycopene (the red compound in tomatoes). We are taking this same approach to study the effects of high-soy diets and tea intake. High soy and tea intake may, in part, explain the lower prostate cancer risk in men living in Asian countries where soy and tea are commonly consumed.

Our recent research demonstrates that whole soy extract has more anti-carcinogenic effects on prostate cancer cells than individual soy isoflavones (genistein and diadzein). This was performed on both early- and late-stage cancer cells in the lab, and whole soy extract proved more effective than isoflavones for both cases.

In other studies, we hormonally induced prostate inflammation in rats. Uncontrolled, long-term prostate inflammation can lead to prostate cancer. We then fed the animals whole soy, green tea, or a combination of soy and green tea. Neither tea nor soy alone showed much effect. However, the combination of soy and tea significantly decreased markers of inflammation and increased levels of an anti-inflammatory protein. This may inhibit hormone-induced inflammation that ultimately contributes to prostate cancer.

Last updated May 2007