Dietary Nutritional Factors

Dietary Fat

High calorie intake has often been associated with an increased risk of prostate cancer. However, the interaction between various compounds (total fat, animal fat, saturated or un-saturated fatty acids, cholesterol, triglycerides, omega-3 fatty acids) is very complex (Wuermli

Micronutrients

Carotenoids are a group of complex unsaturated hydrocarbons occurring as pigments in plants such as carrots (alpha-, beta-, gamma-carotene) or tomatoes (lycopene). Some carotenoids, but not lycopene, are precursors of vitamin A and they have been shown to act as antioxidants and inhibitors of IGF-1. Giovannucci (1999) reviewed

Table 1 Data on dietary and nutritional factors according to evidence levels

Level Ia

No data

Level Ib

(Selenium)

Level IIa

Lycopene

Level IIb

Dietary fat, vitamin E, rye, soya, and phytoestrogens

Level III

Saturated fat, vitamin E, beta-carotene

Cochrane Collaboration

Cochrane Collaboration

72 studies concerning intake of tomatoes and tomato-based products and blood lycopene levels in relation to the risk of various cancers. An inverse association was identified in 57 reports and 35 of them were statistically significant. The evidence for a benefit was strongest for tumors of the prostate, lung, and stomach. Conversely, no study indicated that intake of tomatoes or a high serum lycopene level led to an increased risk of cancer of any site.

Vitamins

Numerous studies could demonstrate an inverse correlation between intake of vitamins and incidence of various types of malignant tumors. Of special interest with regard to prostate cancer were vitamins A, C, D, and E.

Vitamin A (retinol) and its precursor (beta-carotene) are found in foods of animal origin (liver, fish oil) or in carrots and green vegetables (spinach, broccoli), respectively. They act as antioxidants by suppressing the carcinogenic potential of free radicals, enhance the immune system, and induce cellular differentiation. Dose-related side effects include hepatotoxicity, central nervous system changes, and mucocutaneous dry-ness and, therefore, hamper their use in clinical trials (Heinonen et al. 1998).

Vitamin C is a water-soluble antioxidant in fruit and vegetables. The majority of case-control and cohort studies failed to demonstrate any correlation between vitamin C intake or plasma concentrations and occurrence of prostate cancer.

Calcitriol (1,25 dihydroxyvitamin D3) is the active form of vitamin D and responsible for cal cium metabolism in kidneys, bone, and gut. A favorable impact of ultraviolet radiation (sun exposure), which is the main source of vitamin D, on the incidence of prostate cancer has been postulated (Hanchette and Schwartz 1992). In primary cultures of prostatic tissues derived from prostate cancer patients, vitamin D3 carried out antiproliferative effects (Peehl et al. 1994). However, the role of vitamin D in prostate cancer promotion and prevention is still controversial.

Vitamin E (alpha-tocopherol) is a fat-soluble potent intracellular antioxidant occurring in lettuce, watercress, and cotton- and hemp-seed oil. In the Finnish alpha-tocopherol beta-carotene (ATBC) trial, 29,133 male smokers aged 5069 years were randomly assigned to receive al-pha-tocopherol (50 mg), beta-carotene (20 mg), both agents, or placebo daily for 5-8 years (Heinonen et al. 1998). However, in this study prostate cancer was only looked at as a secondary end point. A 32% decrease in the incidence and a 41% decrease in mortality from prostate cancer was observed among the subjects receiving al-pha-tocopherol compared with those not receiving it. Notably, among men receiving beta-carotene, prostate cancer incidence was 23% higher and mortality was 15% higher compared with those not receiving it. Despite these data, results from other epidemiologic studies do not support a general protective effect of vitamin E.

Minerals

Conversion of vitamin D to the active form 1,25 dihydroxyvitamin D3 is suppressed by high consumption of dietary calcium (milk, cheese) (see also Sect. 2.3). Furthermore, low serum calcium levels stimulate the secretion of parathyroid hormone which promotes the conversion of vitamin D to calcitriol. From a clinical point of view, calcium has been found in excess levels to be associated with an increased rate of prostate cancer progression.

Selenium, a trace element occurring predominantly as selenomethionine in dietary supplements (bread, cereals, fish, chicken, meat), is a key component of a number of functional sele-noproteins required for normal health. In a double-blind cancer prevention trial, 974 men with a history of basal cell or squamous cell carcinoma were randomized to either receive 200 |ig selenium daily or placebo for a mean of 4.5 years (Clark et al. 1998). Selenium treatment was associated with a 63% reduction in the secondary endpoint of prostate cancer incidence, but the number of cases was rather low. Long-term selenium intake can be determined in toenails. In a nested case-control study within the Health Professionals Follow-Up Study, high levels of selenium in toenails were correlated with a reduced risk for advanced prostate cancer (Yoshizawa et al. 1998). A more recent prospective case-control study did not find a statistically significant difference in toenail selenium levels of patients with newly diagnosed prostate cancer and matched controls (Lipsky et al. 2004). The National Cancer Institute launched a large randomized trial (SELECT study) with four arms to compare selenium (200 |g) plus vitamin E (400 IU) to either agent alone or to placebo. Results will be available presumably after the year 2012 (Table 1).

Phytoestrogens

The major categories of phytoestrogens include isoflavonoids (genistein, daidzein), flavonoids (quercetin), and lignans (enterolactone). The first two groups are found in vegetables such as beans, peas, and especially soy and in fruits; lig-nans also occur in grains, cereals, and linseeds. The putative biological effects of phytoestrogens are listed in Table 2. In geographic areas with low prostate cancer incidence (Asia, southern Europe) diets are rich in phytoestrogens, which has been confirmed by higher serum levels or urinary concentrations of phytoestrogens compared to Western countries (Adlercreutz et al. 1993). The favorable antitumoral effects of various soy-derived products have been demonstrated in experimental studies; however, clinical data are sparse and assessment of dietary phytoestrogen intake is complex. In an analysis of data from 59 countries, prostate cancer mortality was related to food consumption, tobacco use, socioeconomic factors, reproductive factors, and health indicators (Hebert et al. 1998). Mortality rates were inversely associated with estimated intake of cereals, nuts, oilseed and fish, and soy products were found to be significantly protective.

Kicking the Habit

Kicking the Habit

Stop Thinking About How You're Going To Quit Smoking When You Can Instantly Stomp It In Less Than 30 Days With A Proven Set of Techniques. When your

Get My Free Ebook


Post a comment