CALCIUM ON THE TONGUE Researchers have found that rodent tongues have receptors, or sensors, that respond to calcium. This image shows one of the calcium-sensing receptors stained in the center of a bright green onion-shaped taste bud. Image: Courtesy Michael Tordoff
Mice, and most likely humans, have the ability to taste calcium—and most do not like it, according to new research presented today at the American Chemical Society's semiannual national meeting, held this week in Philadelphia. Scientists say the findings could explain why, according to the U.S. Department of Agriculture, 80 percent of Americans do not get enough calcium when it is so important for our health.
Michael Tordoff, a biologist at the Monell Chemical Senses Center in Philadelphia, suspected that calcium's unpleasant flavor—imagine the bitter taste of chalk, which is mostly calcium—makes people avoid calcium-rich foods like spinach, brussel sprouts and collard greens. He started by trying to figure out whether the tongue could taste calcium.
Tordoff and his colleagues gave 40 different strains of mice a choice: They could drink water or a calcium-rich liquid. Most preferred water once they tried both.
There was, however, one exception—a mouse strain called PWK actually preferred the calcium-enriched liquid. Those mice, it turned out, had a different version of genes that are responsible for taste receptors on the tongue. (Taste buds, which contain approximately 50 to 100 taste cells, comprise receptors for at least five specific tastes—salty, sour, bitter, sweet and umami, or savory.)
Even more surprising: one of the genes was identical to a portion of the receptor that detects both sweet and savory, or hearty, flavors. "That was a totally unexpected, out-of-left-field finding," Tordoff says. "Nobody in their right mind would have ever thought that the sweet-taste receptor was involved in calcium taste because the taste is so different." Although this sweet and savory receptor subunit is involved in calcium taste, it does not seem to trigger the perception of either flavor.
Tordoff has so far studied these genes only in mice, but he speculates that they also play a role in human's calcium taste perception. He suggests that we do have a calcium "appetite" that kicks in when our intake is dangerously low -– for example during pregnancy or dialysis, which depletes calcium levels. People in those states tend to have a strong craving for chalky, calcium-rich cheeses.
Tordoff's findings could inspire technologies that would make calcium-rich foods more palatable, according to Eugene Delay, a taste biologist at the University of Vermont in Burlington. Indeed, San Diego–based biotechnology company Senomyx is currently developing "bitter blockers" that prevent bitter taste cells from responding, so it's not crazy to think the same could be done to block calcium taste, Tordoff says.
The fact that people can taste calcium may also help scientists better understand—and prevent—diseases like osteoporosis. "It would be interesting to see if individuals that are susceptible to osteoporosis have mutations in these [calcium receptor genes]," says Debi Fadool, a biologist at Florida State University in Tallahassee. "Maybe they're supersensitive to calcium, so they just don't want to consume it."