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Prostate Cancer: Nutritional Considerations

Prostate cancer risk appears to be increasing worldwide, a trend that may be due in part to the globalization of Western eating habits. Prostate cancer risk has been associated with higher meat3 and dairy intake4 and diets that are high in processed foods and low in fiber (including processed meat, red meat, refined grains and vegetable oils, and soft drinks).5 Conversely, evidence is accumulating that a low–fat, vegetarian diet may help prevent prostate cancer6 and possibly play a role in its treatment.7,8 The following three principal issues have emerged in research on diet and prostate cancer.

Androgenic Effects

High–fat, low–fiber diets are associated with elevated blood testosterone concentrations, presumably either as a result of increased production or decreased excretion.9,10 In turn, higher testosterone concentrations are associated with increased risk of prostate cancer.11 Men who adopt low–fat, high–fiber diets show about a 15% reduction in testosterone concentrations.9,10

Epidemiologic evidence suggests that prostate cancer risk increases with animal fat intake.12 High intakes of certain animal fat–containing foods in particular (red meat and dairy products) confer twice the risk for metastatic prostate cancer as do the lowest intakes.13

The association between animal product intake and prostate cancer risk may also be mediated by insulin–like growth factor I (IGF–I), a peptide with hormonal actions that increases with animal fat and animal protein consumption.14 Also, carcinogenic heterocyclic amines tend to form as meat is cooked at high temperatures, and these are associated with increased risk of prostate cancer.15

Hormonal Effects of Dairy Products

Two large Harvard University cohort studies, among several other epidemiologic studies, have shown significant increases in prostate cancer risk among the highest consumers of dairy products, independent of fat content.16,17 This correlation may be due to the effect of milk consumption on circulating concentrations of IGF–I.18

However, evidence suggests that calcium may play a role, as calcium supplements have also been linked to prostate cancer risk. Compared with men who have the lowest calcium intake, those with highest intakes appear to have as much as double the risk for developing prostate cancer.19,20 The association may be related to calciumís tendency to suppress the activation of vitamin D from its prohormone form. Among vitamin Dís biological actions is maintenance of cellular differentiation within the prostate.21

Protective Effects of Fruits and Vegetables

Lycopene is an antioxidant in the carotenoid family that imparts a bright red color to tomatoes, watermelon, pink grapefruit, and some other foods. Intake of lycopene–containing foods is associated with a lower risk of prostate cancer.22, 23 Lycopene may interfere with IGF–I and other mediators of prostate cancer risk, such as androgen signaling, oxidative stress, and interleukin–6.24 In a study of men with high–grade prostatic intraepithelial neoplasia, lycopene supplementation (4 mg/d) was associated with a reduction in the number who developed occult prostate cancer, compared with a control group on low–lycopene diets.25

Supplementation with lycopene has also revealed evidence of biochemical and clinical improvement in men with existing prostate cancer.26,27 However, caution regarding supplementation is warranted. Evidence indicates that other constituents of tomatoes, rather than lycopene alone, may be responsible for the apparent oncostatic effect28 seen in humans in one small clinical trial.29 Additional studies are needed to determine the degree to which tomato products, lycopene, or both are useful for the prevention and treatment of prostate cancer.

Intake of cruciferous vegetables (eg, broccoli, cabbage, cauliflower, and Brussels sprouts) is also associated with reduced risk for prostate cancer,30,31 perhaps because these foods can induce phase II detoxification enzymes, as well as cell–cycle arrest and apoptosis in prostate cancer cells.32

The antioxidant selenium may also play a helpful role. In epidemiologic studies, men who consume higher levels of selenium, or have higher levels of selenium in their body tissues, are about half as likely to develop prostate cancer, compared with those with the lowest intakes.33 Preliminary data suggest that selenium supplements (200 μg/d) may reduce prostate cancer risk.34

Two additional diet–related factors merit mention:

Obesity. Some, though not all, studies suggest that obesity may increase the risk for development of prostate cancer, especially in younger men.35 Obesity–related diseases (eg, insulin resistance syndrome) appear to double the risk for prostate cancer.36

Alcohol. A large prospective cohort study found that alcohol was a minor factor in prostate cancer risk, except in men who tend to binge. Compared with abstainers, men drinking 105 grams of alcohol (equivalent to 8–9 drinks) or more per week but who drink on only 1 to 2 days each week had a 60% higher risk.37 Although some evidence suggests that liquor consumption increases risk more than beer or wine,38 other evidence indicates that risk increases with any type of alcohol.39

 

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