Friend or foe? The current epidemiologic evidence on selenium and human cancer risk

Abstract

Scientific opinion on the relationship between selenium and the risk of cancer has undergone radical change over the years, with selenium first viewed as a possible carcinogen in the 1940s then as a possible cancer preventive agent in the 1960s-2000s. More recently, randomized controlled trials have found no effect on cancer risk but suggest possible low-dose dermatologic and endocrine toxicity, and animal studies indicate both carcinogenic and cancer-preventive effects. A growing body of evidence from human and laboratory studies indicates dramatically different biological effects of the various inorganic and organic chemical forms of selenium, which may explain apparent inconsistencies across studies. These chemical form-specific effects also have important implications for exposure and health risk assessment. Overall, available epidemiologic evidence suggests no cancer preventive effect of increased selenium intake in healthy individuals and possible increased risk of other diseases and disorders.

Figure 1:

Number of publications per year yielded a Medline search using the terms “selenium” and “cancer” (solid line) and “selenium,” “cancer,” and “humans” (dotted line).

Figure 2:

Relative risk (RR) for selected cancers in randomized, placebo-controlled trials (with 200 μg of organic Se when not otherwise specified; see Table 2 for references numbers).

Figure 3:

Relative risk (RR) for selected cancers in a natural experiment investigated in Reggio Emilia, northern Italy, where residents consumed drinking water with high inorganic hexavalent Se content (around 8 μg/l) as only distinctive feature (Vinceti et al., 1995, 1998, and 2000 [119, 121, 130]).