Many animal studies have been conducted to evaluate the effects of super nutritional levels of selenium on experimental carcinogenesis using chemical, viral, and transplantable tumor models. Two thirds of these studies found that high levels of selenium reduced the development of tumors at least moderately (14-35% compared to controls) and, in most cases, significantly (by more than 35%) (Whanger 1998).
The impact of selenium supplementation on basal cell carcinoma was studied on 1312 subjects (18-80 years of age, 75% of whom were men) (Clark et al. 1996). Within 6-9 months, the group receiving 200 mcg a day of selenium realized about a 67% increase in plasma selenium levels. The non-supplemented group, although judged “normal” in regard to plasma selenium levels, experienced twice the rate of cancer as those receiving selenium. Researchers concluded that higher amounts of dietary selenium than the amount recommended by the FDA are needed to prevent cancer.
Although the study failed to show the effectiveness of selenium in altering the course of either basal or squamous cell carcinoma, selenium impacted the incidence of other types of malignancies with amazing success. The overall reduction in cancer incidence was 37% in the selenium-supplemented group; a 50% reduction in cancer mortality was observed over a 10-year period (Clark et al. 1996).
The following are the site-specific reductions in cancer incidence observed in the study: colorectal cancers (58%), lung cancer (46%), and prostate cancer (63%). A selenium deficiency appears to increase the risk of prostate cancer four- to five-fold. It was determined that as the male population ages selenium levels decrease, paralleling an increase in prostate cancer (Brooks et al. 2001).
Data is compelling regarding the usefulness of selenium’s protective effects against cancer:
- Selenium-enriched broccoli is protective against chemically induced mammary and colon cancer in rats (Davis et al. 2002).
Note: While selenium is contributing to the lower incidence of malignancy, the anticancer affects of broccoli should also be factored into the defense. Please read the section What Should the Cancer Patient Eat (appearing in this protocol) for valuable information regarding dietary factors affecting patient outcome. - The relationship between serum levels of selenium and the development of upper digestive tract cancer was examined (Mark et al. 2000). The relative risk of esophageal cancer was 0.56 in individuals in the highest quartile of selenium level compared with those in the lowest quartile. The corresponding relative risk of gastric cardia cancer was 0.47. Based on the data, it was concluded that 26.4% of esophageal and gastric cardia cancers are attributable to low selenium levels.
- Adding selenium to salt resulted in a significant reduction in the incidence of cancer (Whanger 1998).
- A significant increase in apoptosis and a decrease in DNA synthesis in breast cancers cells (MCF-7 and SKBR-3) occurred with selenium supplementation. The selenium benefit was just as impressive in cancers of the lung (RH2), small intestine (HCF8), colon (Caco-2), and liver (HepG2). Prostate cancers (PC-3 and LNCaP) as well as colon cancer (T-84), although initially less affected by supplementation, became responsive when selenium was coadministered with Adriamycin or Taxol (Vadgama et al. 2000). This study suggests that selenium potentiates the anti-cancer effects of chemotherapy. Selenium supplementation in patients undergoing radiation therapy for rectal cancer improved quality of life and reduced the appearance of secondary cancers (Hehr et al. 1997).
- It appears that selenium acts as an immunologic response modifier, normalizing every component of the immune system (Ferencik et al. 2003; Arthur et al. 2003)
An important form of selenium is Se-methylselenocysteine. This is the form of selenium found naturally in plants such as broccoli and garlic. A suggested selenium dosage is 200 mcg a day. The optimal dose for cancer patients is unknown at this time, but suggestions have ranged from 200-400 mcg a day depending upon the selenium content of the soil. Foods considered good sources of selenium include Brazil nuts, grains, onions, tomatoes, broccoli, chicken, eggs, garlic, liver, seafood, and wheat germ. Americans typically consume 60-100 mcg of selenium a day from dietary sources.
