Smell is often the most overlooked of our senses, but its loss may be an early warning sign of neurodegenerative diseases such as Parkinson's and Alzheimer's. Research indicates that a diminished sense of smell can appear years before other symptoms emerge, offering a potential window for earlier diagnosis and treatment.
In Parkinson's disease, up to 90% of patients experience smell loss, often before tremors or stiffness develop. By the time motor symptoms appear, more than half of the dopamine-producing neurons in the brain have already been lost. Identifying smell loss as a biomarker could allow doctors to detect the disease much earlier.
The link between smell and neurodegeneration may lie in the olfactory bulb, a brain region that processes scents and connects to areas controlling memory and emotion. In some Parkinson's patients, the disease may start in the olfactory bulb after exposure to inhaled toxins or viruses. For Alzheimer's, damage may begin in the locus coeruleus, a brain stem region that connects to the olfactory bulb.
However, smell loss is not exclusive to these diseases; it can also result from ageing, stress, or other conditions. This makes it a challenging diagnostic tool on its own. Scientists are still working to understand the exact mechanisms, but the potential for early intervention makes this a promising area of research.
