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