Health risk assessment of environmental selenium: Emerging evidence and challenges (Review)

Abstract

New data have been accumulated in the scientific literature in recent years which allow a more adequate risk assessment of selenium with reference to human health. This new evidence comes from environmental studies, carried out in populations characterized by abnormally high or low selenium intakes, and from high-quality and large randomized controlled trials with selenium recently carried out in the US and in other countries. These trials have consistently shown no beneficial effect on cancer and cardiovascular risk, and have yielded indications of unexpected toxic effects of selenium exposure. Overall, these studies indicate that the minimal amount of environmental selenium which is source of risk to human health is much lower than anticipated on the basis of older studies, since toxic effects were shown at levels of intake as low as around 260 µg/day for organic selenium and around 16 µg/day for inorganic selenium. Conversely, populations with average selenium intake of less than 13-19 µg/day appear to be at risk of a severe cardiomyopathy, Keshan disease. Overall, there is the need to reconsider the selenium standards for dietary intake, drinking water, outdoor and indoor air levels, taking into account the recently discovered adverse health effects of low-dose selenium overexposure, and carefully assessing the significance of selenium-induced proteomic changes.

Figure 1.

Number of hits (on the horizontal axis) generated by PubMed search on January 4, 2017 with the MeSH terms ‘selenium’ and ‘humans’ and (‘epidemiology’ or ‘epidemiologic methods’) linked to specific diseases (dark plus light gray areas). Those additionally linked with the additional MeSH terms ‘environment’ or ‘risk’ or ‘assessment and government regulation’ are in light gray (percentage on the total hits on the vertical axis).

Figure 2.

Comparison between environmental and dietary upper and lower standards for selenium (left) and the thresholds of adverse health effects of selenium (right) using an uncertain factor of 3 (dark grey) and of 10 (light gray). Data refer to daily overall selenium dietary intake.