Loss of Smell Could Be Early Warning Sign for Alzheimer's Disease, Study Reveals
A groundbreaking new study has discovered that the loss of smell may function as an early warning signal for Alzheimer's disease, with the timing of diagnosis potentially allowing at-risk patients to access more effective treatments. The research, conducted by the German Center for Neurodegenerative Diseases (DZNE) and Ludwig-Maximilians-Universität München (LMU), found that Alzheimer's can trigger the brain's immune cells, known as microglia, to erroneously attack healthy nerve fibers critical for the sense of smell. This suggests that individuals with Alzheimer's are likely to experience difficulties with smelling years before receiving a formal diagnosis of the disease.
Connecting Scent and Alzheimer's: A Promising Neurological Insight
The link between scent and Alzheimer's has been hypothesized for many years, but the study's findings offer a promising indication that neurologists might begin routinely testing smell sensitivity in patients. Dr. Dale Bredesen, a neurologist at Apollo Health specializing in Alzheimer's disease, explained to HuffPost, "The question has always been, 'Why is smell loss such an early change in Alzheimer's?' I think this study will help to let neurologists know we should be more sensitively testing smell in people routinely before they ever have any cognitive complaints."
Dr. Bredesen elaborated that one of the earliest areas affected in Alzheimer's disease is the locus coeruleus, a region in the brain stem responsible for supplying the brain with norepinephrine. This neurotransmitter plays a vital role in regulating functions such as smell, sleep, and blood flow. The research team employed a combination of mouse models, human brain tissue from deceased patients, and PET brain scans from living Alzheimer's patients to investigate how and why Alzheimer's is associated with smell impairment.
Mechanism Behind Smell Loss in Alzheimer's Disease
The study revealed that Alzheimer's induces abnormal neuron firing, causing phosphatidylserine—a molecule typically located inside neuron membranes—to migrate to the outside. This displacement essentially deceives microglia into perceiving that the fibers are emitting an "eat-me" signal and require elimination. Consequently, the microglia assault the fibers connecting the locus coeruleus to the olfactory bulb, the neural structure in the forebrain that governs the sense of smell, leading to smell loss as one of the initial symptoms to deteriorate.
"The study brings this all together and shows that the locus coeruleus damage, the loss of sense of smell, is probably related to energy," Dr. Bredesen stated, drawing on his expertise. "So the new insight says, 'Hey neurologists, please, look more carefully and more quantitatively at the sense of smell because this can be another of the early warning signs.'"
Implications for Early Diagnosis and Treatment
For individuals at risk of Alzheimer's, experts now recommend requesting a smell test. Current Alzheimer's treatments, such as amyloid-beta antibodies, have demonstrated optimal efficacy when administered to patients as early as possible. If smell tests can help identify at-risk patients years before memory loss symptoms manifest, neurologists may be able to slow the progression of the disease.
"With all these complex chronic illnesses, things are changing when you can pick them up earlier and do something about it," Dr. Bredesen remarked. He compared this development to the hemoglobin A1C test, introduced 50 years ago, which revolutionized pre-diabetes diagnoses, and biomarkers like P-tau217, which can detect potential Alzheimer's patients over two decades before symptom onset. "This is also essentially what happened with Pap smears many, many years ago," he added, referring to the potential of smell tests. "You went from a disease where you would find it late, and women would die from it." While cervical cancer remains a serious health threat, it is now highly preventable and curable when detected early, with deaths decreasing by over 50% since the 1970s due to Pap smears.
Recommendations for At-Risk Individuals
Dr. Bredesen advises that anyone over the age of 35 with a family history of brain cognitive conditions should consider asking their neurologist for a smell test. Lifestyle factors, including regular exercise, a nutritious diet, and social interactions, continue to play a crucial role in prevention. However, it is essential to recognize that a smell test does not provide a definitive answer for at-risk patients.
"If you start noticing some decrease in your smelling ability, please get to a doctor," Dr. Bredesen emphasized. "Don't assume that it's a benign condition." He stressed that studies like this one are guiding neurologists and doctors in the right direction, but individuals at risk of Alzheimer's should not assume that passing a smell test guarantees they are entirely free of the disease.
