The purpose of this site is to provide an overview of literature research that relates dietary intake to prostate cancer. Follow the links below to find out how diet and prostate cancer are linked, the key nutrients related to the development and progression of prostate cancer, and ways that improvements in nutritional intake may reduce one's risk of developing prostate cancer, or limit its progression.

1. Evidence for Links Between Diet and Prostate Cancer
2. Nutrients of Importance in Prostate Cancer and its Prevention
3. Optimizing Nutritional Intake
4. References
5. Links to other information on the web

Evidence for Links Between Diet and Prostate Cancer
Many studies have shown that a person's risk of developing prostate cancer is linked to where they live. For example, a person in North America is much more likely to develop prostate cancer than a person living in Asia. However, the difference is not due to genetics, because, within two generations, men of Asian descent living in North America have the same prostate cancer risk as someone whose ancestors have lived in North America for a much longer period. While the exact reasons for the difference in prostate cancer risk are not known, it is suspected that dietary differences between the two regions may account for the difference. Current knowledge of prostate cancer risk does not provide definitive cause and effect relationships, but evidence is being rapidly acquired, so that general guidelines and approaches can be provided. Nonetheless, this is an area of ongoing research, and these guidelines may evolve as more information is acquired. Early studies (Willett, 1997; Giovannucci, 1995) showed a strong positive correlation between the incidence of prostate cancer and per capita fat consumption in different countries. In addition, when the diets of more than 50,000 health professionals were analyzed, it was found that the men who ate the most fat were almost twice as likely to develop prostate cancer as men who had low fat diets (Health Professionals study, Giovannucci et al., 1993). Similar studies aimed at looking at the role of specific nutrients have suggested that deficiencies of certain vitamins, such as vitamins D and E, may lead to an increased risk of prostate cancer. These studies and others suggest that there are ways that we can optimize our dietary intake to reduce the risk of prostate cancer, and to influence its progression.

back to the top

Nutrients of Importance in Prostate Cancer and its Prevention
Fat:
As previously noted, early studies suggested a strong link between fat intake and risk of prostate cancer. Although subsequent studies have not all been as conclusive, the results generally show a positive relationship. In particular, saturated fats are most strongly implicated. Although a couple of studies have suggested that excessive intake of animal fats, meats and dairy products may increase the risk of prostate cancer, it is worth noting that these diets are often also high in total fat and saturated fat (Clinton and Giovannucci, 1998). It is therefore difficult to separate these interrelated variables and to associate the risk directly with any one of these food items. Nonetheless it would be prudent to choose low fat or lean varieties of these foods. It is worth noting that in the traditional North American diet, approximately 40% of the calories come from fat. The recommended intake is, in fact, that no more than 30% of total calories come from fat. Clearly, for many people there is an opportunity to modify their diets to reduce the fat intake, and thus lower their risk of prostate cancer and other diseases.

Vitamin D:
Vitamin D, along with calcium and phosphorus, are interacting components within a complex network of nutritional and endocrine pathways. The physiologically active form of vitamin D is 1,25 (OH)2-vitamin D. It is a highly regulated hormone, and its concentration varies depending upon levels of calcium and phosphate in the blood. For example, if the dietary Intake of calcium is low, the blood level of 1,25 (OH)2-vitamin D will increase, and vice versa. Thus, modification of vitamin D intake must be considered in tandem with the intake of calcium and phosphorus. Usually, as long as there is adequate intake of vitamin D in the diet, the blood level of 1,25 (OH)2-vitamin D varies little (Clinton and Giovannucci, 1998).
Vitamin D has a clear role in prostate cancer prevention. Epithelial cells in the prostate contain vitamin D receptors, and 1,25 (OH)2-vitamin D has been shown to inhibit proliferation of established prostate cancer cell lines (Miller et al., 1995). Thus, a deficiency in vitamin D can lead to an increased risk of prostate cancer. The Health Professionals Study (Giovannucci et al., 1993) showed that the prostate cancer risk was normal as long as dietary intake of vitamin D was at or near recommended levels. There is no evidence in the literature to suggest that intakes above the recommended levels would reduce the risk of prostate cancer.

Vitamin E:
The role of vitamin E in prostate cancer has not been widely studied. Low blood levels of vitamin E have been linked to an increased risk of prostate cancer (Eichholzer et al., 1996). However, one case-controlled study showed no relationship between vitamin E and prostate cancer (Rohan et al., 1995), and in another study of 29,000 Finnish smokers, daily consumption of a 50 mg supplement of alpha tocopherol (a form of vitamin E) reduced the incidence of prostate cancer and prostate cancer deaths by 30 to 40% (Heinonen et al., 1998). The question has been raised, however, as to whether these results are applicable for non-smokers as well. The recommended intake of vitamin E is 15 mg/day, an amount that is usually present in the typical North American diet. Supplementation beyond these levels should only be done after consultation with your Doctor or Dietitian, because vitamin E can interact with some prescribed medications. For most people, the safe upper limit for intake is 1000 mg/day (ref: Food and Nutrition Board, U.S. Institute of Medicine, April, 2000). Above 1000 mg/day, vitamin E can have a pro-oxidant effect (i.e. it is no longer a protective antioxidant).

Vitamin A and Beta-Carotene:
So far, there is no clear association between prostate cancer risk and vitamin A intake. Some studies have indicated that a deficiency leads to increased prostate cancer risk, while others have suggested that vitamin A supplementation either provides no protection or may lead to an increased risk of prostate cancer (Kamat and Lamm, 1999). The source of vitamin A may be important. In Asia, vitamin A is largely obtained from vegetables, whereas in North America, the main source of vitamin A is fat. Beta-carotene is a carotenoid that can be metabolized to form vitamin A. Like vitamin A, the link between beta-carotene intake and prostate cancer risk is also unclear: intake of beta-carotene has been associated with increased risk, decreased risk, or no effect on the incidence of prostate cancer. A recent trial showed no benefit from beta-carotene supplementation on the risk of prostate cancer (ATBC study group, 1994).

Calcium:
Calcium intake in excess of 2000 mg/day has led to a three-fold increase in the risk of prostate cancer, due to the fact that increased dietary calcium reduces levels of (protective) 1,25 (OH)2-vitamin D (Health Professionals Study, Giovannucci et al., 1993). Risk was independently increased by calcium from both dairy and non-dairy sources, including supplements. The literature does not, however, suggest any increased risk at normal intake levels. Since adequate calcium is necessary for bone health and the prevention of osteoporosis, intake of 1000 - 1200 mg/day is recommended (ref: Food and Nutrition Board, U.S. Institute of Medicine, Sept. 1999).

Lycopene:
Lycopene is a potent antioxidant, and is the major carotenoid in tomatoes. Unlike other carotenoids (e.g., beta-carotene), lycopene cannot be converted to vitamin A. Several epidemiological and clinical trials have shown that diets rich in tomato products and other lycopene-rich foods can reduce the risk of prostate cancer (Giovannucci et al., 1995a and 1999; Clinton et al., 1996). In addition, processed tomatoes contain much more available lycopene than raw tomatoes. A 36% reduction in risk was observed among men that consumed two or more servings of tomato sauce per week, and in general, it has been suggested that the greater the frequency of consumption of tomato products, the greater the reduction in risk.
It is important to realize that approximately 18 different forms of lycopene have been detected in prostate tissues (Clinton et al., 1996), and furthermore, tomatoes contain many other nutrients that may act together with lycopene. Thus, it has not been conclusively determined that lycopene alone mediates the relationship between prostate cancer risk and the consumption of tomato products. At this time, the best recommendation is to increase one's intake of processed tomatoes (sauces, juice, etc.).

Selenium:
Selenium functions through selenoproteins, several of which are oxidant defense enzymes. A strong association between low selenium levels and increased risk of prostate cancer has been reported (Willett et al., 1983). In another trial, the risk of prostate cancer for men receiving 200 mcg of selenium daily was one-third the risk of men receiving a placebo (Yoshizawa et al., 1998). Nonetheless, further studies are required to confirm these preliminary results.

Soy Products:
The consumption of soy-based products and related isoflavones and phytoestrogens is much greater in Asian countries than in North America, and this has been suggested as a possible reason for the decreased risk of prostate cancer for Asian men (Messina et al., 1994). In vitro, isoflavones have been shown to inhibit the growth of androgen-dependent and androgen-independent prostate cancer cells (Peterson and Barnes., 1993), although the mechanism for these inhibitory actions is not known. Further studies are required to better understand the role of soy, isoflavones, and phytoestrogens in prostate cancer.
Given the preliminary evidence relating soy to prostate cancer, it is worthwhile to consider increasing one's intake of soy products. Although there is no guarantee of a direct benefit, soy products are low in fat, and a reduction in fat intake is much more clearly linked to a reduction in prostate cancer risk.

back to the top

Optimizing Nutritional Intake

Foods are complex nutrient packages, and contain many more compounds than the vitamins and nutrients listed below. Other compounds within the food may enhance the protective effects of, for example, antioxidant nutrients, and the carotenoids and isoflavones currently considered to be beneficial may, in fact, simply point to other (as yet unidentified) compounds that actually provide the protective effect.
There is clear evidence that a diet rich in fresh fruits and vegetables reduces the risk of many diseases, including cancer. The specific reasons and nutrients responsible for this protective effect have not all been identified, and are not completely understood. The protective effect is likely related to complex interactions between constituent phytochemicals that have not all been identified, let alone incorporated into supplements. Thus, consumption of supplements and food extracts may not provide the same benefits as fresh fruits and vegetables. In essence, it is almost always better to improve one's intake through food sources.
The first step towards improving nutrient intake is to understand what you are currently consuming. A diet analysis based on an accurate 5-day food intake or a food frequency questionnaire is an excellent starting point. Based on the results, it can be determined if you need to increase or reduce the intake of certain nutrients within your diet. Based on recent studies, you should pay attention to the following:

i) Reduce fat intake to no more than 30% of total calories, and decrease intake of saturated fat while increasing intake of omega 3 fatty acids

• Many foods are sources of fat for the body. Fruits and vegetables contain very small amounts of fats. Most of the fat in the diet comes from added fat, such as margarine, oil, butter, sauces, salad dressings, and gravies.
• Meats, milk, and milk products can also provide a significant amount of fat. Commercially prepared foods, such as cookies, cakes, and doughnuts are another source of fat.
• To reduce the amount of fat in the diet, choose lean and lower fat foods and reduce the amount of fat added during cooking and at the table. Consumption of lower fat milk products, lean meats and alternates can greatly reduce the total amount of fat in the diet.
• Use lower fat cooking methods, such as baking, microwaving, steaming, or broiling. Use nonstick pans to reduce the need for oil during cooking.
• To increase your intake of omega-3 fats (a "good" polyunsaturated fat), consume salmon, trout, sardines, herring or mackerel, flaxseeds and flax oil, walnuts, pumpkin seeds, dark leafy vegetables, wheat germ, canola oil and soy products.
  

back to the top

click here for a printable version of this page