A method for monitoring a blood glucose level of an individual comprises the steps of receiving (S1) a first glucose value, which has been measured in a body fluid of the individual other than the individual's blood, the first glucose value representing the blood glucose level of the individual with a first delay； receiving (S6) speech of the individual； analyzing (S7) the individual's speech； and determining (S8) a supplementary glucose value, which represents the blood glucose level of the individual with a shorter delay than the first delay； wherein the determination of the supplementary glucose value is based on the analyzing of the individual's speech. A device and a system for performing the method are also disclosed.
