Solanidine is a sensitive and specific dietary biomarker for CYP2D6 activity.

"Declarations Ethics approval and consent to participateAll study participants gave written informed consent. The study protocols were approved by the Coordinating ethics committee of the Hospital District of Helsinki and Uusimaa. Consent for publicationNot applicable. Competing interestsThe authors declare that they have no competing interests. Competing interests The authors declare that they have no competing interests."

"Funding Open Access funding provided by University of Helsinki (including Helsinki University Central Hospital). This study was supported by grants from European Research Council (Grant Agreement 282106), the Sigrid Jusélius Foundation and State funding for university-level health research (Helsinki, Finland). Johanna I. Kiiski was supported by the Sakari Alhopuro Foundation."