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.

Source: Elson M. Haas M.D. (Excerpted from Staying Healthy with Nutrition: The Complete Guide to Diet and Nutritional Medicine)