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Does Your Memory Pass the Smell Test?

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For many of us, the ability to smell the world around us is something we take for granted. If there’s something cooking in the oven, we delight in the delicious odors wafting from the kitchen. On a spring day, flowering plants release a pleasing odiferous palate we savor every time we inhale. But the act of detecting odors is anything but a simple process that’s guaranteed to function correctly for everyone. It represents the brain’s complicated interpretation of intricate sensory information detected by nerve tissue in our nostrils. And if something goes wrong with that process it can be a sign of serious health issues – in the brain and elsewhere in the body. Here’s what you need to know… When your ability to smell things slips it can signal health problems ahead. According to researchers at the University of Rochester Medical Center in New York, when your olfactory nerves interpret the smells picked up by your nose, the neurological information gets transferred into your brain through an interwoven network of nerve connections that include what are called centrifugal fibers. They have found that these fibers act as a switch that toggles between two different patterns to help the brain understand what odors your nose is picking up. The first basic process is like a quick snapshot that helps you gain an initial understanding of the smell. Then the second set of connections helps the brain track how the smell changes over time.1 Now, for reasons that have not been fully explained, a collection of studies shows that when things go wrong with this neurological process – causing a poor sense of smell – it can mean an increased chance of death.

Loss of Smell Linked to Increased Risk of Death 

A 13-year investigation at Michigan State University that involved more than 2,000 people aged 71 to 82 found that the folks who had trouble detecting odors had a 50 percent greater chance of dying within ten years.2 Michigan State researcher Honglei Chen, MD, PhD, warns that, "Poor sense of smell becomes more common as people age, and there's a link to a higher risk for death.” Dr. Chen notes that a weak sense of smell can be an early indicator of Parkinson’s disease and Alzheimer’s disease, as well as other forms of dementia. But in his study, those conditions only accounted for 28 percent of the increased risk. And he can’t explain what other factors are involved. "We don't have a reason for more than 70 percent of the increased risk," says Dr. Chen. "It tells us that in older adults, impaired sense of smell has broader implications of health beyond what we have already known. Incorporating a sense of smell screening in routine doctor visits might be a good idea at some point."

Losing Your Smell to COVID 

You’ve heard – or perhaps experienced first-hand – that a COVID-19 infection can steal your sense of smell, at least temporarily. Exactly why this happens has not been definitively explained, but research at Johns Hopkins indicates that inflammation linked to the disease is the cause. The loss of smell doesn’t come directly from infection of the nose or brain by the virus.3 “Our findings suggest that SARS-CoV-2 infection of the olfactory epithelium leads to inflammation, which in turn, damages the neurons, reduces the numbers of axons available to send signals to the brain and results in the olfactory bulb becoming dysfunctional,” says Hopkins researcher Cheng-Ying Ho, MD, PhD.

Restoring Sense of Smell 

Meanwhile, research is underway to find ways to restore a sense of smell in folks who have lost it. Researchers at Tufts have developed a way to grow and maintain olfactory stem cells which might be used to restore odor-sensing tissues in the nose for people who have lost those types of cells. At the same time, collaborations between researchers at the Harvard Medical School and Virginia Commonwealth School of Medicine are ongoing to create brain implants to help people with brain injuries detect odors. None of that research, unfortunately, seems close to yielding tangible results. So, if you have a dependable sense of smell then you should treasure it and pay attention to any changes to your sniffer. But if it starts to slip, beware. You may want to get a thorough medical checkup to see if a serious medical condition is threatening your health.

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