If you lack selenium, supplements are good for you, if you have enough they could raise your risk of developing diabetes type 2, says a study published Online First in The Lancet. The authors explain that the number of people taking selenium supplements has grown considerably over the last few years
Study author, Margaret Rayman from the University of Surrey, Guilford, UK, said:
"The intake of selenium varies hugely worldwide. Intakes are high in Venezuela, Canada, the USA, and Japan, but lower in Europe. Selenium-containing supplements add to these intakes, especially in the USA where 50% of the population takes dietary supplements."
Selenium is a trace mineral that is essential to good health in small amounts. Higher selenium intake or status (levels in the blood) have been demonstrated to improve male fertility, provide some protection against bladder, lung, colorectal system, and prostate cancers, and have antiviral effects. Low selenium intake or status as been associated with increased risk of poor immune function, cognitive decline, and death.
However, evidence indicates that this mineral has a limited therapeutic range and that high levels of selenium may have detrimental effects, such increasing the risk of type 2 diabetes.
The use of selenium supplements has become extensive over the last decade, primarily due to the theory that it can decrease the risk of developing cancer and other diseases. Based on the results of observational studies, selenium supplements have been marketed for numerous conditions. Although, results from human trials to confirm the effectiveness of these supplements has differed.
These differing results are because the studies were conducted in different populations with different genetic backgrounds and selenium status, according to Rayman.
Rayman states that the differing results can be explained by the fact that selenium supplements, as for many nutrients, only benefits individuals when they lack certain nutrients.
According to Rayman, individuals with low blood selenium levels are most likely to receive the greatest benefit from selenium supplementation. However, to date, the largest trials have been conducted in countries like the USA, were selenium status is good. More trials are required in populations with low selenium status.
In addition, the study indicates that the interaction between genetic background and selenium intake or status could be vital - individuals could be either less genetically receptive to the benefits of selenium-containing proteins (selenoproteins) in the body or to selenium supplements, or more receptive:
"Since polymorphisms is selenoproteins affect both selenium status and disease risk or prognosis, future studies must genotype participants."
"The crucial factor that needs to be emphasized is that people whose blood plasma selenium is already 122 µg/L or higher - a large proportion of the US population (the average level in American men is 134 µg/L) - should not take selenium supplements. However, there are various health benefits, and no extra risk, for people of lower selenium status (plasma level less than 122 µg/L), who could benefit from raising their status to 130-150 µg/L - a level associated with low mortality."