A theoretical calculation of the charge density in metallic K is used to estimate pressure induced changes in the electron-capture decay constant &lgr;e, of 40K. It is predicted that &lgr;e goes through a maximum at approximately 3.5-fold compression and approaches its one atmosphere value at pressures corresponding to those in the outer-core of the earth. The maximum predicted change of about 4¿104 years in the halflife is negligible when compared to the current experimental uncertainties, which are of the order of 107 years.