Scientists have sounded warning bells over high consumption of supplements of selenium, a mineral found in soil and foods, as it can spur increased type-2 diabetes risk.
Selenium is vital for health in tiny amounts. Low selenium levels have been tied to higher death risk, poor immunity function and mental decline.
But a new review study of clinical trials has shown mixed results from selenium supplements. In certain cases, more of selenium seems to have adverse effects, the medical journal The Lancet reports.
This indicated that the supplements only benefit people with too little selenium in their diet, said Margaret Rayman, professor at the University of Surrey, Britain, according to the Daily Mail.
"The intake of selenium varies hugely worldwide. Intakes are high in Venezuela, Canada, the US and Japan but lower in Europe. Selenium-containing supplements add to these intakes, especially in the US where 50 percent of the population takes dietary supplements," she said.
The supplements should not be taken by people whose blood levels of selenium were already 122 micrograms per litre or higher, she argued. The average level in American men was 134 micrograms per litre.