People who find Brussels sprouts unbearably bitter may also find a health upside to their keen sense of taste. The ability to taste such bitterness may be linked with an increased capacity to fight bacterial respiratory infections.
Bitter taste receptors were traditionally thought to be located only on the tongue; however, new research shows these receptors are also found in the linings of the nasal and sinus cavities. Additionally, the study showed these receptors are involved in activating the immune system's protection against common bacterial infections.
The receptors work as "an early detection system," which warns the immune system about bacterial invaders and activates the body's defenses, said study author Dr. Noam Cohen, director of rhinology research at the University of Pennsylvania.
But not everyone benefits from these receptors: nearly a third of people in Europe and the U.S. do not have the specific version of the bitter taste-receptor gene, called TAS2R38, that activates an immune response.
The results could lead to new ways to treat the nearly 1 in 10 people in the U.S. who have chronic rinosinusitis, a condition of constantly inflamed and swollen sinuses, the researchers said.
The findings appeared Oct. 8 in the Journal of Clinical Investigation.
A bittersweet finding
In their study, researchers grew cells in lab dishes, forming structures that resembled the multilayered lining of the nose and sinus, to test out how bitter receptors affect the initial stages of the infection process. Results showed that chemicals produced by common bacteria called Pseudomonas aeruginosa activated the TAS2R38 bitter receptor, and caused the hair-like cilia that line the sinuses to start sweeping away microbial intruders. The activation also resulted in the release into the sinuses of nitric oxide, which kills bacteria.
The researchers noted that they looked at just one of 25 bitter receptors. It remains unclear if the other receptors affect the immune system, or how many bacteria may tip off the warning system.
In the past, researchers have used the chemical phenylthiocarbamide (PTC) to identify people with functional bitter receptors. Those who can taste PTC are classified as supertasters, having functioning bitter receptors, while those who can't taste the chemical are non-tasters, lacking these receptors.
People who would say that Brussels sprouts taste bitter are likely to be supertasters, having responsive bitter receptors, the researchers said.
The new findings also suggest that supertasters may have a higher risk of chronic sinusitis, and that non-tasters have more upper respiratory infections. Upon testing nasal tissue samples from patients who had undergone surgery related to sinus problems, the researchers found that none of the 11 supertasters had Pseudomonas bacteria in their tissues, whereas seven out of 20 non-tasters had infections.
"If you are a supertaster, it’s going to be very rare that you're going to get… sinusitis," Cohen said. However, the bitter-tasting ability doesn’t protect against all infections, he added.
Could a taste test tell how often people get sick?
This research could lead to a nearly cost-free test that could distinguish supertasters from the more susceptible non-tasters, said Thomas Finger, co-director of the Rocky Mountain Taste & Smell Center, who was uninvolved in the research.
The new findings also suggest that certain bitter compounds could be used to activate the immune system. For example, a bitter nasal spray could be used to ward off an infection in the early stages, Finger said. However, such potential therapies are a long way off, he said.
Next, the researchers will look at whether genetics plays a role in people's responses to sinusitis treatments, Cohen said.