A survey at the University of Chicago of 3,000 adults between the ages of 57-85 found that 39% with the poorest sense of smell were dead within five years; contrasted with only 10% who identified odours correctly. While the loss of smell sense obviously does not cause death directly, it may be an early indicator of mortality risk.
Mundasad, S. (2014). Sense of smell ‘may predict lifespan’. London: BBC Health News, October 1st 2014.
This relates to:
Jayant, M. Pinto, KE. [and] Wroblewski, DW. [et al]. (2014). Olfactory dysfunction predicts 5-year mortality in older adults. PLoS ONE. October 1st 2014; 9 (10): e107541.
The following NHS Choices Behind the Headlines critical appraisal supplies more information about this research and some considered perspective:
Does losing your sense of smell predict death risk? London: NHS Choices Behind the Headlines, October 2nd 2014.