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Smoking cigarettes and drinking alcohol can wreak havoc on the organs, but what do these two vices do to the senses?
Considering what's known, overdoing it presumably damages a person's sense of smell and taste. It’s a warning most health websites echo and many studies continue to back up. However, the work of Richard Doty, PhD, the director of the Penn Smell and Taste Center, along with colleagues at Harvard University, suggests it may be more nuanced.
In a recent study in BMJ of over 3,500 men and women, Doty, Harvard’s Gang Liu and their colleagues found that many heavy drinkers had impaired taste but not smell, while most light to moderate drinkers were left unscathed and even fared better on smell tests than people who didn’t drink.
Though past studies by Doty and others blame smoking for disrupting the senses, this time, that wasn’t the case. “Interestingly,” he said, “there is some evidence that the bad habit of smoking may ultimately protect, to some degree, people’s sense of smell.”
Those are just a few unexpected observations from this large and most current representative study of taste and smell issues in Americans. It’s based on data from the National Health and Nutrition Examination Survey, a periodic assessment of the nation’s health conducted by the National Institutes of Health (NIH).
To gauge smelling abilities, the NIH relied on the widely used Pocket Smell Test, which has people sniff chocolate, strawberry, smoke, leather, soap, grape, onion and natural gas. Failing to identify six out of those eight odors indicated a problem. Taste impairment was defined as failing to correctly identify a bitter taste (quinine) or salt.
Altogether, the BMJ authors estimated that 43 million Americans over the age of 40 suffer from smell and/or taste problems, and that they are linked to a slew of factors, including ethnicity, age, cardiovascular disease and history of cancer and asthma. Check out the full study to read more about these influences.
Among the bigger drivers behind taste problems was heavy amounts of alcohol.
Consuming more than four drinks of alcohol a day was associated with a significantly higher prevalence of taste impairment compared to people who didn’t drink. Anything less than that didn’t raise any red flags.
Alcohol seems more forgiving on the nose. All drinkers were less likely to have a smell impairment, the data showed. In fact, light to moderate drinkers were significantly less likely to have a smell problem compared to people who didn’t drink, which suggests that casual drinking may even protect the sense of smell, Doty said.
When people drink, the alcohol activates the receptors in their nose or on their taste buds, triggering nerve fibers connected to the brain to generate an experience: “Ah, that’s fruity,” or “Hmm, that’s hoppy.”
It is possible the amount of alcohol consumed has a distinct effect on the nerve endings that mediate smell and taste, or what the authors call people’s “chemosensory perception.” It may explain why taste was impaired in heavy drinkers and light drinkers were less likely to have smell issues.
“We think any damage is occurring in these nerve fibers and receptors or cells associated with the senses,” Doty said. “Although, we now know that alcoholism and poor diet that leads to thiamine deficiency (vitamin B1) can also damage central brain regions important for both smell and memory.”
The smoking data was the most surprising, Doty said.
It has long been reported that the habit can affect both smell and taste. His own study in 1990 in JAMA found that higher levels of smoking affected smell, and a 2014 study published in the journal Chemosensory Perception found that smoking can dull taste buds.
The results in the BMJ study, however, suggest that smoking does not always adversely impact the ability to smell, and that other factors, such as amount of smoking, sex, age, and genetic predispositions, may be involved.
This isn’t the first time findings like this have surfaced. The paper pointed to another cross-sectional study from researchers in Spain who reported in 2012 in BMJ “that smoking and exposure to noxious substances were even mild protective factors for smell recognition.” Another study from Doty, published in Movement Disorders in 2015, found that current smokers with Parkinson’s disease outperformed those with Parkinson’s who never smoked on a smell identification test with 40 different odors.
Other studies have found that smoking may decrease the risk of Parkinson’s in the general population, suggesting the possibility that nicotine may have some neuroprotective qualities.
“Damage to the nicotinic neurotransmitter system is one of the better correlates to a wide range of disorders,” said Doty, who has treated over 6,000 patients since the early 1980s, when the Smell and Taste Center opened at Penn. “Nicotine stimulates that system. Conceptually, if that system gets stimulated more, it may protect against damage that ultimately may be causing sensory problems and even some neurological diseases.”
Doty isn’t advocating for smoking, but the work does support further research to better understand the BMJ data as well as to find new, non-addictive ways to potentially treat patients with nicotine or some similar compound, he said.
Set to publish online in Lancet Neurology later this month, Doty’s newest study further explores the relationship between smell dysfunction and neurological diseases. Past studies of his, as well as others in the field, have indicated smell issues could be a harbinger of future disease.
“It’s possible that rather than disease-specific pathology, plaques for instance, it’s the damage to forebrain neurotransmitters that will better explain the degrees of smell and serve as a marker for these difference diseases,” he said.