In a 2014 article in PLOS ONE, more than 3,000 adults aged 57 to 85 were measured for their olfactory function (their sense of smell). They were asked to correctly identify the scents of rose, leather, orange, fish, and peppermint. Those who could identify one or none of the smells were considered to be anosmic, which means their sense of smell had lost its normal function. If they could identify all the scents, they were considered normosmic. The researchers followed up with the participants five years later to check on their health status or whether they had died.
Among the normosmic people, just 10% died after five years compared to the 39% of anosmics who died. Those who had lost their sense of smell were five times more likely to die within the five-year time frame than those with normal olfactory function. After controlling for overall health, level of frailty, and demographics, those who had lost their sense of smell had three times the risk of death than those with a normal sense of smell. This mortality risk was higher than heart disease, diabetes, and stroke.