Is there a relationship between changing body odour and Alzheimer's disease?
The available studies say nothing about whether Alzheimer's disease changes a person's own body odour. What is well documented is that people with Alzheimer's disease lose their sense of smell early in the disease process, and that persistent smell loss is a reason to discuss this with your doctor.
Body odour does not change as a primary symptom of Alzheimer's disease, according to the available studies. What is well documented, however, is the reverse: people with Alzheimer's disease themselves smell worse. Loss of smell occurs early in the disease process and affects the recognition, discrimination, and perception of odours.
On smell-identification tests, people with Alzheimer's disease score lower than healthy peers of the same age. They are not alone in this: in Lewy body dementia the smell impairment is even more pronounced, which makes smell loss a more nuanced diagnostic signal. Similar pathways of smell loss have also been described in Parkinson's disease, where the loss of certain nerve cells in the brain plays a role. Whether the same mechanism also explains Alzheimer's disease has not yet been proven, but is being investigated.
A small study showed an interesting reverse effect: odours can actually activate autobiographical memories in Alzheimer's patients that are normally difficult to access. The memories were more specific and came to mind more quickly. This effect was not found in healthy individuals. The study was small, so this is not yet a proven therapy, but it is striking enough to warrant further investigation.
Smell loss is not exclusively a harbinger of dementia. A large-scale study of more than 2,000 older adults found that people with poorer smell scores also had a higher risk of depressive symptoms later in life. The association ran partly through cognitive decline, not through inflammation. Smell loss can therefore be a signal for several things at once.
The question of whether Alzheimer's disease changes a patient's body odour cannot be answered by the available studies. What they do show is that the ability to smell is one of the earliest and most consistent signs of the disease process: if you or someone around you notices that smells are no longer being recognised, that is a reason to discuss this with a doctor.
All claims are based on observational studies, one case report, and one mouse study. There are no RCTs or meta-analyses examining the relationship between body odour as an emitted substance and Alzheimer's disease. The claim about body odour changing (in the sense of how a person smells to others) is not addressed in the source texts.