Is there a relationship between changing body odour and Alzheimer's disease?

Loss of smell is one of the earliest signs of Alzheimer's disease. It occurs before memory decline becomes noticeable, and is consistently described in multiple reviews as an early clinical indicator. There is therefore indeed a link between Alzheimer's disease and changes in the sense of smell, although strictly speaking this concerns the perception of someone else's odour (or the loss of one's own sense of smell) rather than the body odour that others detect on a person.

In Alzheimer's disease specifically, the problem is not a 'broken nose' but changes in the brain. People with dementia struggle mainly with recognising and naming odours, more so than with the basic detection of them. This suggests that higher-level odour processing in the brain is affected, rather than the olfactory nerves themselves.

Whether Alzheimer's disease also changes the body odour that others perceive is being investigated through volatile chemical compounds that the body releases via the skin, breath and faeces. Such compounds could in theory become a non-invasive diagnostic marker. This research is still in its early stages, however: no clinically usable test is yet available.

As a diagnostic tool, odour-discrimination tests are showing initial promising results. In a study of 90 participants, such a test distinguished early Alzheimer's patients from people with normal cognition with 94% accuracy. Loss of smell was also found in other research to be able to predict the transition from mild cognitive complaints to Alzheimer's disease. These are encouraging early figures, but they have not yet been confirmed in large groups. Smell testing is also insufficient to distinguish Alzheimer's disease from other forms of dementia. It works better as a complement to other biomarkers or brain scans than as a stand-alone test.