A group of scientists studied a group of over 1,000 older people who weren't sick or suffering dementia. They gave each person a test to see how well they could identify 12 familiar odors. Those with the lowest scores had a much higher probability of dying over the next year than those who couldn't.
There's more at the link.
My father complained that he was no longer able to smell much, several months before he died. I wonder if this is generally true? If so, it may be a useful indicator . . . but then, wouldn't it also be pretty scary?
"Honey, do you like the smell of my new perfume?"
"Er . . . I'm afraid I can't smell it at all, honey."
"Eek! Oh, no! I'm going to be a widow!"