Document Type



The concern of this study was with a systematic consideration of the effects of subject, season of the year, and the female menstrual cycle on intra- and interindividual variability of body potassium mass, as measured by whole- body 40K counting. Six subjects—two males and four females—were measured frequently during four 30-day testing periods approximating late spring, late summer, late fall, and mid-winter. Statistical analysis showed a tendency of body potassium to increase from summer to fall, and to decrease from fall to winter. Analysis of subject effect on body potassium showed considerable variation which cannot be accounted for by weight or any other single factor. Analysis of the effect of the menstrual cycle on body potassium in females showed that the variation that occurs is specific to individual, and that, generally, there is less variability in phase 1 of the menstrual cycle than in phases 2 and 3.