This is not the first time researchers have identified this as an early warning sign.

But loss of smell could also be an early warning sign that you're at risk for Alzheimer's disease.

A recent study published in the Journal of Alzheimer's Disease provides additional evidence that loss of smell is a warning sign for mild cognitive impairment (MCI) related to Alzheimer's disease.

Also known as anosmia, loss of smell has been identified as an early indicator of Alzheimer's in previous studies.

Data published in Biosensors in 2018 found that sense of smell worsened as patients progressed from MCI to Alzheimer's disease.

As a result, researchers suggested designating "olfactory dysfunction"—that is, disruptions to your sense of smell—as a way to identify those at risk for Alzheimer's disease even before MCI symptoms appear (also known as the preclinical stage).

This may explain why the loss of smell is an early warning sign for MCI and eventually Alzheimer's disease, as it was "closely tied" to the level and progression of neuropathological damage.

Of these patients, 11 cases were associated with Alzheimer's disease, three with vascular dementia, and one with frontotemporal dementia.

When looking at these patients' PET scans, those with lower olfactory scores had higher levels of Alzheimer's pathology in their brains, and those whose sense of smell declined over time also had higher amyloid and tau levels in some regions related to smell and memory function.