Cruciferous Vegetables

Cruciferous vegetables (broccoli, cauliflower, cabbage, Brussels sprouts) contain sulforophane, which has anti-cancer properties. A case-control study in China found that intake of cruciferous vegetables, measured by urinary secretion of isothiocyanates, was inversely related to the risk of breast cancer; the quartile with the highest intake only had 50% of the risk of the lowest intake group [89]. In the Nurses' Health Study a high intake of cruciferous vegetables (5 or more servings/week vs less than two servings/week) was associated with a 33% lower risk of non-Hodgkin's lymphoma [90]. In the Health Professionals Follow-up Study bladder cancer was only weakly associated with low intake of fruits and vegetables, but high intake (5 or more servings/week vs 1 or less servings/wk) of cruciferous vegetables was associated with a statistically significant 51% decrease in bladder cancer [91]. Also, prostate cancer risk was found to be reduced by cruciferous vegetable consumption in a population-based case-control study carried out in western Washington state. Three or more servings per week, compared to less than one serving of cruciferous vegetables per week resulted in a statistically significant 41% decrease in prostate cancer risk [92]. Similar protective effects of cruciferous vegetables were seen in a multi-ethnic case-control study [93]. A prospective study in Shanghai, China found that men with detectable amounts of isothiocyanates in their urine (metabolic products that come from cruciferous vegetables) had a 35% decreased risk of lung cancer. Among men that had one or two genetic polymorphisms that caused them to eliminate these isothiocyanates slower there was a 64% or 72% decreased risk of lung cancer, respectively [94].

Broccoli sprouts have a very high concentration of sulforophane since this compound originates in the seed and is not made in the plant as it grows [95,96]. One sprout contains all of the sulforophane that is present in a full-grown broccoli plant. So, if sulforophane is especially cancer-protective, it would seem reasonable to include some broccoli sprouts in an anti-cancer diet.

Selenium

Selenium is a mineral with anti-cancer properties. Many studies in the last several years have shown that selenium is a potent protective nutrient for some forms of cancer. The Arizona Cancer Center posted a selenium fact sheet listing the major functions of selenium in the body [97]. These functions are as follows:

1. Selenium is present in the active site of many enzymes, including thioredoxin reductase, which catalyze oxidation-reduction reactions. These reactions may encourage cancerous cells to under apoptosis.

2. Selenium is a component of the antioxidant enzyme glutathione peroxidase.

3. Selenium improved the immune systems' ability to respond to infections.

4. Selenium causes the formation of natural killer cells.

5. P450 enzymes in the liver may be induced by selenium, leading to detoxification of some carcinogenic molecules.

6. Selenium inhibits prostaglandins that cause inflammation.

7. Selenium enhances male fertility by increased sperm motility.

8. Selenium can decrease the rate of tumor growth.

A serendipitous randomized, double-blind, controlled trial of a 200 μg/day selenium supplement in the southeastern region of the USA (where soil selenium levels are low) found that the primary endpoints of skin cancer were not improved by the selenium supplement, but that other cancer incidence rates were decreased by selenium [98,99]. There was a significant reduction in total cancer incidence (105 vs 137 cases, P = 0.03), prostate cancer (22 vs 42 cases, P = 0.005), a marginally significant reduction in colorectal cancer incidence (9 vs 19 cases, P = 0.057), and a reduction in cancer mortality, all cancer sites (40 vs 66 deaths, P = 0.008) (selenium versus control group cases reported, respectively) [98]. The selenium supplement was most effective in ex-smokers and for those who began the study with the lowest levels of serum selenium. Several prospective studies have also examined the role of selenium in cancer prevention, particularly for prostate cancer, summarized in Table 2.

Overall, it appears that poor selenium levels, especially for men, are a cancer risk. If a person has low selenium levels and other antioxidant defenses are also low the cancer risk is increased even further. Women do not appear to be as sensitive to selenium, as breast cancer has not been found to be influenced by selenium status in several studies [100-104], although both men and women were found to be protected by higher levels of selenium from colon cancer [100] and lung cancer [105,106]. Good vegetarian sources of selenium are whole grains and legumes grown in selenium-rich soil in the western United States, brazil nuts (by far the most dense source of selenium), nutritional yeast, brewers yeast, and sunflower seeds.

Chlorophyll

All green plants also contain chlorophyll, the light-collecting molecule. Chlorophyll and its derivatives are very effective at binding polycyclic aromatic hydrocarbons (carcinogens largely from incomplete combustion of fuels), heterocyclic amines (generated when grilling foods), aflatoxin (a toxin from molds in foods which causes liver cancer), and other hydrophobic molecules. The chlorophyll-carcinogen complex is much harder for the body to absorb, so most of it is swept out with the feces. The chemoprotective effect of chlorophyll and its derivatives has been tested in laboratory cell cultures and animals [107,108]. There is so much compelling evidence for anti-carcinogenic effects of chlorophyll that a prospective randomized controlled trial is being conducted in Qidong, China to see if chlorophyllin can reduce the amount of liver cancer cases, which arise from aflatoxin exposure in their foods (corn, peanuts, soy sauce, and fermented soy beans). A 55% reduction in aflatoxin-DNA adducts were found in the group that took 100 mg of chlorophyllin three times a day [109]. It was supposed that the chlorophyllin bound up aflatoxins, but there were chlorophyllin derivatives also detected in the sera (which had a green tint to it) of the volunteers who took the supplement, indicating a possible role in the body besides binding carcinogens in the gut [110].