Rubidium is present in the earth's crust, in seawater, and in the human body. Our body contains about 350 mg. It has not yet been shown to be essential. Chemically, it is like potassium, and in some animals it can replace potassium in certain functions, though this does not seem to be the case in humans. Rubidium can possibly be a potassium antagonist in regard to absorption and utilization, though this needs further investigation.
Rubidium is absorbed easily from the gut, about 90 percent. It is found generally throughout the body, with the least in the bones and teeth; it is not known to concentrate in any particular tissue. Excess rubidium is eliminated mainly in the urine.
Sources: Food sources of rubidium have not been researched very well as yet. Some fruits and vegetables have been found to contain about 35 ppm. Rubidium may also be found in some water sources.
Functions: There are currently no known essential functions of rubidium. In studies with mice, rubidium has helped decrease tumor growth, possibly by replacing potassium in cell transport mechanisms or by rubidium ions attaching to the cancer cell membranes. Rubidium may have a tranquilizing or hypnotic effect in some animals, possibly including humans.
Uses: There are no clear uses for rubidium as yet. Because of its possible tranquilizing effect, it could help in the treatment of nervous disorders or epilepsy.
Deficiency and toxicity: There is no known deficiency or toxicity for rubidium.
Requirements: There is no RDA for rubidium. The average dietary intake may be about 1.5 mg. daily.