Rubidium is an alkali metals which appears with lithium, sodium, potassium, cesium and francium down the left-hand side of the periodic table.
It is a soft silvery-white metal, that melts on a really hot day (40 C) and reacts violently with water.
Discovered by the World’s most famous chemist, Robert Bunsen of Bunsen burner fame, it was named for the ruby-red lines at the far-right of the emission spectrum produced when salts containing the element are placed in the flame of a Bunsen burner.
|Flame emission spectrum of rubidium. Image source.|
Sodium and potassium are essential dietary elements. Lithium, which precedes, and rubidium, which follows, sodium and potassium in the alkali metals series of the periodic table are likely also essential elements in the mammalian diet, since a deficiency of either causes stunted growth and abortion in goats. Also suggestive of a biological function in humans, rubidium concentration in blood plasma is under homeostatic regulation at a concentration of about 12 parts per million.
Designation of an element as essential requires, however, demonstration of a specific metabolic function, and the role, if any, of rubidium in human metabolism is unknown. What is known, is that rubidium, like lithium, has psychotropic properties. In particular, rubidium has anti-depressant properties, and has been reported effective in treating lithium-resistant bipolar II depression, a mood disorder unaccompanied by mania.
Rubidium is not useful in the treatment of more typical bipolar, or manic-depressive illness, because at the high pharmacological dose necessary to combat the depressive phase of the illness it intensifies the manic phase.
But like lithium, Rubidium has psychotropic properties in trace amounts far below those that have been used in the clinical treatment of bipolar disorder. In particular, depression in dialysis patients is associated with depletion by around 50% in tissue rubidium concentrations and can be treated by supplementation with trace amounts of rubidium that restore normal tissue concentrations.*
To revert to the question with which we began, “Are you deficient in rubidium?” the probability is that you are not. Rubidium is relatively abundant (100 ppm in the earth’s crust) and widely distributed. But daily dietary intake of rubidium has been observed to vary in America from just over one to almost 5 milligrams per day, which raises the possibility that some diets are deficient in this mineral.
* Caterina Canavese, Ester DeCostanzi, Lino Branciforte, Antonio Caropreso, Antonello Nonnato and Enrico Sabbioni. 2001. Depression in dialysis patients: Rubidium supplementation before other drugs and encouragement? Kidney International 60, 1201–1201.