Aging is epidemiologically linked to an increased incidence of hypertension, impaired glucose tolerance and overt non-insulin dependent diabetes mellitus type II (NIDDM). The cellular basis underlying this clinical and epidemiological linkage, cytosolic free calcium (Ca(2+)(i)) and cytosolic free magnesium (Mg(2+)(i)) levels were investigated in elderly subjects and in subjects with essential hypertension (EH) and metabolic diseases. It has been observed that normal aging, as well as hypertension and NIDDM, is characterized by elevated Ca(2+)(i) and suppressed Mg(2+)(i) levels. Furthermore, the divalent ionic defect displayed in EH and NIDDM resembled the normal aging process, i.e., ionic levels in both young and elderly subjects with EH or NIDDM were indistinguishable from those in healthy elderly subjects. The ionic levels predict quantitatively also the extent of elevated blood pressure, and hyperinsulinemic response to oral glucose challenge. Altogether, we suggest that the missing link, responsible for the frequent and increasing clinical coexistence of hypertension, insulin resistance, impaired glucose tolerance, and NIDDM with age, may be ionic in nature, and intrinsic to the normal aging process in Western man.