Protective Vitamins

Vitamin B-12

Vitamin B-12 has not been proven to be an anti-cancer agent, but there is some evidence indicating that it could be beneficial. The form of administered vitamin B-12 may be important.

Some experimental cancer studies have been carried out with various forms of vitamin B-12. Methylcobalamin inhibited tumor growth of SC-3 injected into mice [111], and caused SC-3 mouse mammary tumor cells to undergo apoptosis, even when stimulated to grow by the presence of growth-inducing androgen [112]. Methylcobalamin, but not cyanocobalamin, increased the survival time of mice bearing implanted leukemia tumor cells [113]. 5'-deoxyadenosylcobalamin and methylcobalamin, but not cyanocobalamin, were shown to be effective cytotoxic agents [114]. Methylcobalamin also was able to increase survival time and reduce tumor growth in laboratory mice [115].

Laboratory mechanistic evidence for the effects of vitamin B12 were seen in a laboratory study with vitamin B-12 deficient rats. Choi et al [116] found that the colonic DNA of the B-12 deficient rats had a 35% decrease in genomic methylation and a 105% increase in uracil incorporation, both changes that could increase risk of carcinogenesis. In two prospective studies (one in Washington Country, Maryland and the Nurses' Health Study) a relation between lower vitamin B12 status (but not deficiency) and statistically significant higher risk of breast cancer was found [117,118]. So, there is evidence from laboratory studies, prospective cohort studies, and mechanistic studies showing that vitamin B-12 is an important nutrient for genetic stability, DNA repair, carcinogenesis, and cancer therapy.

Folic Acid

Folic acid is the dark green leafy vegetable vitamin. It has an integral role in DNA methylation and DNA synthesis. Folic acid works in conjunction with vitamin B-6 and vitamin B-12 in the single carbon methyl cycle. If insufficient folic acid is not available uracil is substituted for thymidine in DNA, which leads to DNA strand breakage. About 10% of the US population (and higher percentages among the poor) has low enough intakes of folic acid to make this a common problem [119]. As shown in Tables 3 and 4, many studies have found a significant reduction in colon, rectal, and breast cancer with higher intakes of folic acid and their related nutrients (vitamin B-6 and B-12). Alcohol is an antagonist of folate, so that drinking alcoholic beverages greatly magnifies the cancer risk of a low-folate diet. Genetic polymorphisms (common single DNA base mutations resulting in a different amino acid encoded into a protein) in the methylenetetrahydrofolate reductase and the methionine synthase genes which increase the relative amount of folate available for DNA synthesis and repair also reduces the risk of colon cancer [120-123]. Cravo et al [124] used 5 mg of folic acid a day (a supraphysiological dose) in a prospective, controlled, cross-over study of 20 patients with colonic adenoma polyps. They found that the folic acid could reverse DNA hypomethylation in 7 of 12 patients who had only one polyp.

Folate may be more important for rapidly dividing tissue, like the colonic mucosa. Therefore, the cancer risk associated with low folate intake is probably higher for colon cancer than for breast cancer. Most of the breast cancer studies only found a protective effect of folate among women who consumed alcohol (see Table 4). However, among women residents of Shanghai who consumed no alcohol, no vitamin supplements and ate unprocessed, unfortified foods there was a 29% decreased risk of breast cancer among those with the highest intake of folate [125]. So, there may be a true protective effect that is masked in the western populations by so many other risk factors. Two studies showed that the risk of cancer due to family history can be modified by high folate intake, so a prudent anti-cancer diet would be high in dark green leafy vegetables. The mean intake of folic acid on the Hallelujah Diet was 594 μg/day for men and 487 μg/day for women [88].

Vitamin D

Vitamin D is produced primarily from the exposure of the skin to sunshine. Even casual exposure of the face, hands, and arms in the summer generates a large amount of vitamin D. In fact, simulated sunshine, equivalent to standing on a sunny beach until a slight pinkness of the skin was detected, was equivalent to a 20,000 IU oral dose of vitamin D2 [126]. (Note that the RDA is 400 IU for most adults.) It has been estimated that 1,000 IU per day is the minimal amount needed to maintain adequate levels of vitamin D in the absence of sunshine [126], and that up to 4,000 IU per day can be safely used with additional benefit [127].

The concentration of the active hormonal form of vitamin D is tightly regulated in the blood by the kidneys. This active hormonal form of vitamin D has the potent anti-cancer properties. It has been discovered that various types of normal and cancerous tissues, including prostate cells [128], colon tissue [129], breast, ovarian and cervical tissue [130], pancreatic tissue [131] and a lung cancer cell line [132] all have the ability to convert the major circulating form of vitamin D, 25(OH)D, into the active hormonal form, 1,25(OH)2D. So, there is a local mechanism in many tissues of the body for converting the form of vitamin D in the body that is elevated by sunshine exposure into a hormone that has anticancer activity.

Indeed, 25(OH)D has been shown to inhibit growth of colonic epithelial cells [133], primary prostatic epithelial cells [134], and pancreatic cells [131]. So, the laboratory work is confirming what had been seen some time ago in ecological studies of populations and sunshine exposure.

The mortality rates for colon, breast, and ovary cancer in the USA show a marked north-south gradient [135]. In ecological studies of populations and sunlight exposure (no individual data) sunlight has been found to have a protective effect for prostate cancer [136], ovarian cancer [137], and breast cancer [138]. Recently Grant found that sunlight was also protective for bladder, endometrial, renal cancer, multiple myeloma, and Non-Hodgkins lymphoma in Europe [139] and bladder, esophageal, kidney, lung, pancreatic, rectal, stomach, and corpus uteri cancer in the USA [140]. Several prospective studies of vitamin D and cancer have also shown a protective effect of vitamin D (see Table 5). It could be that sunshine and vitamin D are protective factors for cancers of many organs that can convert 25(OH)D into 1,25(OH)D2.