A prolonged stay in microgravity has various negative effects on the human body; one of these problems is a noticeable demineralization of bone tissues. Such effects are quite similar to those experienced by subjects on earth affected by osteoporosis; therefore it seems quite straightforward to adopt a similar pharmacological therapy during the stay in the space. In this paper a first step in the identification of a monitoring procedure for the bone demineralization in microgravity, as well as some guidelines for the choice of adequate therapies are given. Such a procedure is based on a mathematical model of the interaction of the most relevant blood and urine indicators of bone demineralization. Specifically, some bone metabolites have been identified, which are relevant to the phenomena and are feasible to be evaluated in the space. Moreover, a model to foresee the evolution of these parameters in the space, depending on the therapy chosen, is provided. The model is derived from the experience of doctors and experts, hence it is based mainly on linguistic information; such an information is codified by means of fuzzy numbers, in order to take into account their uncertainty.