Results from the Linxian Intervention Trial were published in 1993. (60) The trial determined that gastric cancer incidence (relative risk (RR) 0.84, 95% confidence interval (CI) (0.71-1.00)), cancer mortality (RR 0.87, 95% CI 0.75-1.00), especially stomach cancer mortality (RR 0.79, 95% CI 0.64-0.99) were reduced in the groups receiving 30 β-carotene, vitamin E and selenium compared to the groups receiving other vitamin/mineral combinations.” FDA commented that “these results cannot provide clear evidence of an effect of selenium per se. The relevance of these results to the general population, which does not have the same high incidence of stomach cancer or malnutrition, is uncertain.” In commenting on this intervention trial in its qualified health claim approval letter, FDA did agree that the trial “provided some evidence that a selenium-containing supplement had some effect on lowering cancer mortality.” (1)
In the 2004 SU.VI.MAX Intervention Trial, Hercberg et al. reported that incidence of digestive tract cancers for men was only 111 per 100,000 person years for the selenium and antioxidant supplemented group compared to 160 per 100,000 person years for those receiving the placebo. (55)
Also in 2004, Li et al. studied the combined effect of selenium and garlic extract (allitridum) on cancers of the alimentary system. (98) A double-blind intervention study was performed on the participants aged (35 - 74) years, who had matched at least one of the following criteria: (1) a medical history of stomach disorder, (2) a family history of tumor, or (3) smoking and/or alcohol consumption. A total of 2,526 and 2,507 persons from Qixia County, Shandong Province, China were randomly enrolled into intervention group and control group respectively. Each person of the intervention group orally took 200 mg allitridum every day and 100 mcg selenium every other day for one month of each year during November 1989 to December 1991. At the same time, people in control group were given 2 placebo capsules containing corn oil with the identical appearance to that in the intervention group.
In the first five-year follow-up after intervention (1992-1997), there were 35 and 51 cases of malignant tumors found in the intervention group and control group, respectively. The morbidity rates of all malignant tumors were 186.53/10 and 271.49/10 person-year, respectively. The morbidity rates of all cancers in the intervention group declined by 22% compared to the control group. For gastric cancer there were 10 and 19
cases and the incidences were 53.29/10 and 101.14/10 person-year in the two groups respectively: the rate of the intervention group declined by 47.3% compared with the control group. The researchers concluded, “the present study proves that large doses of allitridum and selenium may effectively prevent gastric cancer, especially in men.”
The above studies are consistent with the credible evidence of a protective effect of selenium in decreasing the risk of stomach cancer. It is not scientifically valid to argue that intervention trials using multiple nutrients including selenium necessarily do not apply to selenium alone and thus can not be included in the total body of scientific evidence. The anti-cancer effect of selenium would be demonstrated in trials of multiple nutrients provided that sufficient selenium was used. The other nutrients may or may not have additional anticancer effects, but the body of scientific evidence suggests it is the selenium that is the major factor in any combination of nutrients. It can not be validly argued that the trial results do not necessarily apply to each nutrient separately and thus, in turn, arbitrarily eliminate the anticancer effect of each separate nutrient individually. The fallacy being that to do so ignores the demonstrated anti-cancer effect. Trials finding anticancer effects that include selenium along with other nutrients must be considered supportive, but not conclusive, of an anticancer effect of selenium.