Effect of oral contraceptives on body water and electrolytes.

The effects of sequential oral contraceptives on intracellular and extracellular body water exchangeable body potassium sodium and chloride and serum electrolyte values in 14 patients and 5 control subjects were studied. Measurements were made at midcycle and end-cycle by radioisotopic dilution and radioactivity-counting techniques. Body composition parameters for midcycle and end-cycle showed no change though there was a significant increase in body sodium between the patients and controls (p less than .01) which was not reflected in serum values. Serum electrolyte values did not change significantly in either group. Body water and intracellular water increased and exchangeable chloride decreased in control subjects at midcycle. The results indicate that the increased body sodium which is most likely induced by estrogen has a stabilizing effect on body water since body water fluctuations were less in the contraceptive group than in the controls. Since the increased sodium levels may be implicated in certain oral contraceptive side effects it is recommended that the prescription of oral contraceptives to patients with cardiac or renal disorders or with hypertension be cautiously undertaken.