Not Smelling Death

April 3, 2015

By Medical Discovery News

Not Smelling Death

This may be Debbie Downer question, but can you guess what condition is most indicative of a person’s imminent demise? It turns out that the strongest predictor of impending death is not cancer, stroke, heart attack, diabetes, or emphysema, but a person’s declining sense of smell.

Scientists at the University of Chicago have revealed that the loss of the sense of smell, officially called olfactory dysfunction, is a significant forecaster of death in older Americans. In this study, 3,005 people aged 57-85 were asked to identify five common scents: peppermint, fish, rose, leather, and orange. Five years later, the health of the same people was evaluated.

As this was an older population, some of the subjects died before the study contacted them again. The surprise was that almost 40 percent of those who died had failed the scent test, identifying only one or none correctly. Anosmia is the technical term for complete loss of the ability to smell, while hyponosmia is the significant (but not total) loss of smell. The mortality rate for those with anosmia was four times higher than for those with normal smell. Those who were hyponosmic had an intermediate mortality compared to normal individuals. So being either anosmic or hyponosmic is associated with an increase in a person’s  mortality. And because of the limited length of this study and the relatively small group examined, the effect on mortality is probably underestimated.

Overall, these results are striking. Since these were older individuals, the possibility of other factors influencing these results was examined. The study ruled out confounding factors such as nutrition, mental health, smoking, alcohol abuse, frailty, and neurodegenerative diseases in the results. Those at a higher risk for anosmia or olfactory loss were males, those who were overweight or obese, and those with a lower socioeconomic status.

While the human sense of smell is not as dominant as in other mammals (such as dogs), it is associated with good health and nutrition. The sense of smell is strongly tied to an array of brain functions and is the strongest sense tied to individual memory. Remembered scents can provoke intense memory responses and can stimulate memories from long ago.

The sense of smell is also highly connected to other parts of the central nervous system. Unique among the senses, normal olfactory function relies on cellular regeneration of the specialized sensory cells lining the inside of the nose. If the olfactory system is not working properly, these cells won’t regenerate like they are supposed to do.

Recently, we reported on a study that determined that human noses are capable of distinguishing between at least a trillion different scents. It now appears that the loss of this ability is an omen of death. The exciting part is that a simple scent test taking less than five minutes could become a powerful new way to identify those at high risk of upcoming mortality and lead to interventions that could prolong people’s lives.

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We Are Out-Smelling Ourselves

Jan. 16, 2015

By Medical Discovery News

We Are Out Smelling Ourselves

Dogs are commonly known for their strong sense of smell. Their noses can detect when someone is pregnant, has cancer, even blood glucose levels. But the human nose is pretty amazing too. You may already know that smell is the strongest sense tied to memory – it can provoke intense responses and can seemingly bring back memories from long ago. Recently, a study has determined that our noses are capable of distinguishing between at least a trillion different scents, much more than previously believed.

The common theory was that we could only discern about 10,000 different odors, so this new estimate is a huge jump. Compare that with our ability to discriminate between 2.3 and 7.5 million different colors, which vary in wavelength and intensity, and about 340,000 different tones, which vary in frequency and loudness.

Back in 1927, a study proposed that there were four elementary odor sensations with sufficient resolution for humans to rate each elementary odor sensation on a nine-point scale. Doing the math, they estimated the number of discernable odors to be nine to the fourth power or 6,561, which was later rounded up to 10,000. Since then, that number has been accepted in both popular and scientific literature. But some scientists suspected that this number was too low. After all, we have just three receptors for light yet we can see millions of colors. Since human noses have about 400 different smell receptors that work in concert, the number of smells we can perceive is likely to be much higher the original estimation.

Natural odors are usually mixtures of large numbers of diverse components. The scent of a rose is produced by a mixture of 275 components, only some of which are chiefly responsible for the aroma. Researchers tested human ability to smell using 128 different molecules that are odorants, mixing them in many unique combinations. They then asked how much (or how little) two mixtures had to differ before the human nose could detect two separate smells.

Although they used many familiar smells like orange and spearmint, they intentionally mixed them to produce unfamiliar odors. Since this equals thousand to millions of odors, the study used methods similar to those used by political polls that use a sample to represent the general population. Each person was given three vials at a time, each consisting of 10, 20, or 30 different compounds. Two contained the same mix of odors while the third was different. Each subject was asked to smell about 500 different odorants in all.

Two vials of odorants had to differ by at least 49 percent to be distinguished. That means two vials of odorants could be 51 percent identical and humans could still tell them apart! Overall, scientists estimated that the human nose can distinguish at least 1 trillion scent combinations. Keep in mind, however, that this estimation is based on only 128 different odors. In the real world, many more odors exist in varying combinations so the number of smells discernible by the human nose could actually be much higher.  Of course, there was large variability in the abilities of different people to discern different smells.

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Do We Smell the Same Thing?

Feb. 7, 2014

By Medical Discovery News

Do We Smell the Same Thing?

Have you ever wondered if we all sense the world in the same way? Evidence suggests that the sense of smell is highly individualized, based on genetic differences. This could revolutionize scents and food flavors into custom-designed creations for individuals.

Humans have specialized neuronal cells within the lining the nasal cavities, part of what’s called the olfactory epithelium. The surface of these cells, like much of the nasal cavity, is covered with mucus. Odor molecules dissolve into this layer and are detected when they bind to receptors on the neurons. This sets off a string of biochemical events that produces a signal, which travels along the olfactory nerve to the olfactory bulb of the brain. Then that signal is transferred to different regions of the brain’s cerebrum. Here odors can be distinguished and characterized. These signals are stored in long-term memory, which is linked to emotional memory. That’s why particular smells can evoke memories. This process is quite complex due to the highly evolved sense of smell in humans.

The genes that are involved in olfactory or smell sensations are not well understood. People do perceive odors differently, but researchers have only identified genes for certain odors. For example, human perception of cilantro has been linked to the olfactory receptor OR6A2 and grassy odors have been linked to receptor OR2J3.

New Zealand scientist Dr. Richard Newcomb tested the ability of almost 200 people to smell 10 different chemicals associated with the key odors of things like apples and blue cheese. Then these individuals’ genomes were completely sequenced, and genetic variances that could account for these olfactory differences were determined. For four of the chemicals tested, clusters of genes were identified as being able to detect these odors. Interestingly, these genes were located on different chromosomes. Newcomb’s work almost doubled the number of genes known to be connected with the sense of smell. For beta-ionone, a chemical associated with the smell of violets, a single gene was shown to allow people to sense that fragrant flower’s scent. Overall, the result of this study was that people are capable of experiencing chemical smells in different ways.

This opens the door for scientists to define an individual’s olfactory profile. If it’s understood how an individual perceives smells, a chef could personalize food just for their senses. Imagine walking into a restaurant and handing your server a card with your olfactory profile based on your genes. And violá! A dinner prepared with the seasonings and flavors you find most pleasing. With continued research, our sense of smell may be able to experience this scenario and more. 

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A Whiff of Flavor

By Medical Discovery News

June 30, 2012

Most would agree that the best part of eating is the flavor and taste of food. But what is the difference between flavor and taste? Not everyone can appreciate the difference between them.

The truth is, even for scientists, taste is easier to explain. That’s partly because taste is definitive and limited to five types: sweet, sour, bitter, salty and umami, otherwise known as savory.  People detect these different tastes when molecules from food bind with receptors on the tongue.

Flavor, by contrast, is more complex, and scientists are now learning that flavor’s role in the human brain is powerful. Rather than being sensed by tastebuds, flavor is actually experienced in the brain, and the sense of smell is the key component. A recent book called “Neurogastronomy” by Gordon Shephard, a neurobiology professor at the Yale School of Medicine, focuses on this subject. He explores how the brain’s perception of flavor impacts eating habits such as food preferences and cravings. Flavor presents food in its full dimension, which is why the smell of popcorn makes a person’s mouth water while evoking good memories at the same time. As enjoyable as that may be, the downside of flavor is people make poor food choices, contributing to today’s high obesity rates.

Years of research are helping scientists understand how flavor works. It’s created by the sense of smell. When a person chews and swallows, they’re also breathing. The process of inhaling pulls chemicals released by food into the nasal cavity where they are detected by sensors.  This is called “retrosmell.”  When these signals are transmitted to the brain, a spatial pattern is created. That means the brain creates a smell image, just as a visual image is formed from what is seen.

From there, flavor can further engage the brain by interacting with higher, cognitive regions that control emotion and memory, creating more excitement for or reward from food.  Shepard believes flavor’s role in the brain has an impact on modern social, behavioral and medical issues – particularly on the challenges many people face in making healthy food choices.

If flavor indeed plays such a large role, it goes against a school of thought among evolutionary biologists that the sense of smell has waned. Early research shows as primates evolved into humans, the number of functional olfactory receptor genes declined.  But recent studies, including Shepard’s book, argue people make up for the loss of receptors with retronasal smell, olfactory brain areas, and language. If human smell perception is better than previously thought, it may have been quite important in human evolution.  Its significance continues to play out. After all, who can resist their favorite treats?

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