In a study of adults aged 40 to 90 years who were followed for 10 years, poor smell was linked with an increased risk of dying.

During the study, 411 of 1774 participants (23%) died. After controlling for demographic, health-related, and cognitive confounders, each additional correctly identified odor lowered the risk of mortality by 8%. Individuals who performed at chance level on tests (indicating complete olfactory loss) were at a 19% higher risk of death than individuals with normal smell function.
The results contribute to the growing evidence that olfactory assessments might provide insights on the aging brain.
“Our results were not explained by dementia, which was previously linked to smell loss. Instead, mortality risk was uniquely predicted by smell loss,” said Dr. Jonas Olofsson, senior author of the Journal of the American Geriatrics Society study. “In our future research, we will try to pinpoint the biological processes that can explain this phenomenon.”

Source: Wiley

Full bibliographic information:
Smell Loss Predicts Mortality Risk Regardless of Dementia Conversion. Journal of the American Geriatrics Society.