Burning Mouth Syndrome, Supertasters, and the World's Sweetest Strawberry
While at Yale Medical School in the early 1990s, Dr. Linda Bartoshuk sprang to national attention for her discovery that roughly one in four people were born with an unusually large number of structures containing taste buds, allowing them not only to experience the flavor of foods in far more vivid ways but also to experience greater pleasure from food than an average person with far fewer taste buds.
She dubbed them “supertasters,” a major discovery in a research career spanning five decades, dedicated to helping solve mysteries behind the subtlety of how humans experience taste and when that can result in a disorder.
“It’s wonderful,” said Bartoshuk, now a Bushnell Professor of Food Science and Human Nutrition at the University of Florida. “Good science keeps circling back to the great problems.”
But she soon found out that not all was equal among the population of supertasters.
Bartoshuk estimates that the label applies to 35 percent of women and only 15 percent of men in the United States. “For the average person, the strongest sweet you’ve ever tasted does not taste the same to a supertaster,” Bartoshuk said. “For a supertaster — more often women — it’s twice as sweet.”
Supertasters, Taste Loss, and Menopause
However, there can be a real downside to being a supertaster, especially for peri- and postmenopausal women. Studies have shown between 10 and 40 percent of women seeking treatment for menopausal symptoms complain of burning mouth syndrome, or BMS, which is a painful recurring or regular sensation of oral burning with no clear origin.
In 1998, Bartoshuk received one of the first grants from Women’s Health Research at Yale and confirmed her suspicion that burning mouth syndrome in postmenopausal women was caused by an abnormal activation of the oral pain center in the brain linked to supertasters.
Normally, the tastes of foods activate nerves in the tongue that send taste messages to the brain, which in turn relay messages to block oral pain.
Bartoshuk’s lab discovered that patients with BMS are often supertasters who have experienced severe taste losses on the fronts of their tongues that leave them virtually unable to taste bitter, and her WHRY-funded study explained why postmenopausal women are at special risk for BMS. Specifically, although the loss of taste is most likely caused by a viral illness, the viral damage leaves a woman without the normal inhibition of the brain’s oral pain center, and the resulting activity creates abnormally intense effects.
Sex hormones influence the ability of women to taste bitter. For example, tasting bitterness intensifies early in pregnancy as a selective advantage that evolved to help pregnant women better avoid poisons. When sex hormones decrease during menopause, the intensity of bitter tastes are reduced, resulting in less inhibition of the brain’s oral pain center.
“When you put it all together, women who are born supertasters, are postmenopausal, and have experienced damage to their sense of taste are at a high risk for developing burning mouth syndrome,” Bartoshuk said.
“Think of these sensory connections along an evolutionary path aided by natural selection,” she said. “Imagine that millions of years ago, an animal had to fight with its sharp teeth to survive. Teeth are very close to the tongue, and an injury to the tongue might lead an animal not to eat. But if an animal takes a bite of food and pain is reduced, the animal will be rewarded for eating despite the injury. Consequently, it is more likely to survive to pass this trait along to the next generation.”
But when there is enough damage to the taste sensors on the tongue, the messages from the brain to block oral pain no longer arrive. As a result, an individual can feel what is called an oral phantom — a sensation in the absence of any physical stimulus.
Bartoshuk credits much of her lab’s success to working with talented colleagues, students, and postdocs including Dr. Valerie Duffy, now Director of the Graduate Program in Allied Health Sciences at the University of Connecticut.
Importantly, data from her WHRY-funded study provided the critical science that confirmed the clinical observations her colleague, Dr. Miriam Grushka, now an oral pain specialist in Toronto, found in using medications to treat BMS. For example, the drug clonazepam, which promotes the inhibition of brain activity, helped reduce burning mouth pain in about 70 percent of patients. And we now know that it works by “replacing” the inhibition of the oral pain center lost because of damage to taste, Bartoshuk said, opening the door to finding other treatments as well.
The Fruit of the Future
Bartoshuk’s current research has begun to link with her earlier WHRY-funded work on oral phantoms by focusing now on how taste buds are only part of the story when it comes to mouth sensations and the flavors we experience from food.
When we sniff fruit, volatiles are drawn into our noses and stimulate the olfactory receptors at the top of the nasal cavity. When we eat fruit, chewing releases these volatiles, and they travel up behind our palates and into our noses from the rear. This backdoor to smell and the sensations detected by taste buds on tongues combine to form flavor.
Since the 1970s, scientists have known that some volatiles could intensify sweetness, but in more than 30 years of research, only about a dozen of these volatiles had been identified, Bartoshuk said. While aiming to restore taste to supermarket tomatoes bred for color and hardiness, she and her colleagues discovered how to identify the volatiles in fruit that enhance sweetness. They now have more than 80.
“This is a new source of sweetness, and it means we can make fruit better,” she said. “Imagine strawberries you don’t have to add sugar to. We’re going to make strawberries sweet naturally.”
Bartoshuk hopes her work with volatiles will help show new ways to treat oral phantoms. And she expressed gratitude for WHRY’s part in showing her how studying women can pay great dividends.
“It was awfully welcome funding when we got it,” she said, noting the difficulty of generating funding for innovative gender-based research without preliminary data derived from such initial support. “And it has motivated a lot of research since then and led us to making new discoveries that will benefit both women and men.”
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