The oral glucose tolerance test (oGTT) was performed twice in patients
under long-term lithium treatment. Blood glucose and plasma insulin were determined. The
oGTT results were evaluated by three criteria (Köbberling-Creutzfeldt, WHO, and Epidemiological
Study Group of the European Diabetes Association) and were compared to two
representative reference studies from normal populations. The frequency of impaired glucose
tolerance in the patients was three times higher than expected on the basis of the
studies on normal populations. The variability of the oGTT curves between the first and
second tests as well as the steepness of the time-course of the ‘insulinogenic index’ suggested
mild disturbances of carbohydrate metabolism (mild diabetes) in some of the patients. It is
considered unlikely that the impairment of glucose tolerance in the patients was a direct
pharmacological effect of lithium salts. The possible role of age, sex, manic-depressive
disease, additional medication, and particularly obesity in the effects of long-term lithium
treatment on glucose tolerance is discussed. The authors suggest that the oGTT should be
carried out periodically in long-term, lithium-treated patients over the age of 40 years in
order to detect abnormalities in their carbohydrate metabolism.