In a study in China, researchers found a highly significant association between low levels of selenium in the blood and a high incidence of esophageal and gastric cancers. The study, published in the
Journal of the National Cancer Institute, led researchers to estimate that over 25% of esophageal and gastric cancers in China were due to low levels of selenium.
Selenium is an essential trace element that is necessary for the formation and function of at least 13 proteins. Studies performed in animals have shown that increasing the dietary intake of selenium can lead to a reduction in the incidence of some cancers. As a result, in recent years, many studies have been designed to explore the link between selenium levels and the development of cancer in humans. Researchers speculate that selenium may play a role in the repair and prevention of oxidative damage.
In this study, researchers evaluated the relationship between selenium levels and the subsequent development of esophageal and gastric cancers. To do this, they selected subjects from the General Population Trial of Linxian, China, which was a large trial (29,584 subjects) designed to test four different combinations of nutritional supplements over a period of 5.25 years. One year prior to the start of the General Population Trial, all subjects had blood drawn and stored.
For the new study, researchers evaluated the results from the General Population Trial and selected a large group of subjects who had developed cancer as well as a large group of subjects with no cancer. Overall, researchers selected 1079 case subjects (590 with esophageal cancer, 489 with gastric cancer) and 1062 control subjects. They then measured the selenium levels from the blood that was drawn prior to the original study.
The researchers found a highly significant relationship between low levels of selenium and the subsequent development of esophageal and gastric cancers. The average selenium levels were approximately 4% higher in the control subjects than in the subjects with cancer. Individuals in the highest quartile of selenium developed esophageal and gastric cancers at half the rate as individuals in the lowest quartile.
Furthermore, one year after having blood drawn, approximately half of the 2,141 subjects in this study began taking a supplement that included selenium, beta-carotene, and vitamin E as part of the General Population Trial. The subjects who received this particular supplement had significantly lower rates of esophageal and gastric cancers (both incidence and mortality) than those who did not. However, despite the reduced risk resulting from the supplement, the researchers found that the relationship between selenium levels and cancer risk did not change regardless of whether or not subjects received the supplemental selenium. The researchers speculated that while the supplement could reduce risk, this particular dose might not be capable of immediately changing long-term low levels of selenium.
The researchers concluded that selenium might play a role in the prevention of esophageal and gastric cancers. More research is necessary to determine whether the results of this trial have implications for the U.S. population. Typically the selenium levels in the U.S. population are higher than those of the Chinese population in this study. Furthermore, the major risk factors for esophageal and gastric cancers in the U.S. are smoking and alcohol consumption. Some of the other risk factors associated with these cancers, such as obesity, reflux disease, and Barrett’s metaplasia, are virtually absent in the Chinese population. Research will be ongoing to determine the role that selenium plays in the prevention of cancer. Individuals interested in the prevention of esophageal, gastric, and other cancers may wish to ensure that their diets include adequate amounts of selenium. (Journal of the National Cancer Institute, Vol 92, No 21, pp. 1753-1763, 2000).