Calcium is something of a double-edged sword. Too much of the essential element is as dangerous as too little, either case adversely affecting health in animals from humans to mice to fruit flies.
Sensing calcium at all can be crucial. Though it doesn’t fit into the five established tastes the tongue’s receptors can identify — sweet, sour, salty, bitter and savory (umami) — humans can taste it, and describe it as slightly bitter and sour.
Your body needs it to build and maintain strong bones. Your heart, muscles and nerves also need it to function properly. Some studies suggest that calcium, along with vitamin D, may have benefits beyond bone health: perhaps protecting against cancer, diabetes and high blood pressure.
If you don’t get enough of it you could face health problems related to weak bones:
- Children may not reach their full potential adult height.
- Adults may have low bone mass, which is a risk factor for osteoporosis.
Many Americans don’t get enough of it in their diets. Children and adolescents are at risk, but so are adults age 50 and older.
New research conducted by scientists at UC Santa Barbara and colleagues in Korea has established that calcium taste also exists in fruit flies (Drosophila melanogaster). The team also uncovered a unique class of gustatory receptor neurons (GRNs) necessary for its taste in these model organisms. Surprisingly, given that some calcium is necessary to sustain life, the flies were indifferent to low levels and averse to high levels. The findings appear in the journal Neuron.
“We wanted to understand the underlying mechanisms used to respond to the presence of calcium in food,” said senior author Craig Montell, UCSB’s Duggan Professor of Molecular, Cellular, and Developmental Biology and Neuroscience. “We not only identified the taste neurons but also found three receptor proteins that are important in sensing it. In fact, eliminating any one of them allowed us to do an interesting survival experiment.”
The investigators used petri dishes with one side containing solely sugar (fructose) and the other a mix of sugar and a high level of calcium. Normal flies that rejected the high-calcium side and ate only pure fructose survived. Mutant flies — those in which any one of the three newly found GRNs was removed — were unable to distinguish the two halves of the petri dish. As a result, they consumed enough of the calcium to cause viability problems and, over time, died.
“It turns out that fruit flies don’t have a mechanism for sensing low calcium even though it’s good for them, but they are trying to guard against consuming too much calcium,” Montell explained.
“Surprisingly, we found that calcium avoidance occurred through two mechanisms: activation of a unique class of GRNs, distinct from those that sense bitter compounds and which cause a stop-feeding signal when activated. In addition, calcium inhibits sugar-activated GRNs,” he added. “In humans, high calcium is associated with many diseases and can even be life threatening. Our results suggest that its taste might function primarily as a deterrent in wide range of animals, including humans.”
Story Source: University of California – Santa Barbara.