Hair Cortisol and Other Hair Analytes Decline With Storage Over a One-Year Period: A Systematic, Within-Subject Investigation

This study investigated the impact of storage duration on hair cortisol and other analytes over a 12-month period, using samples from 81 participants. Results showed significant decreases in concentrations of hair cortisol (-28.0%), cortisone (-23.7%), progesterone (-43.9%), OEA (-33.8%), and 1/2-AG (-69.9%) after 12 months. Notably, declines were evident after six months for several analytes and even after three months for progesterone. The study concludes that extended storage adversely affects analyte quality, recommending analysis within six months of sampling and emphasizing the importance of transparent reporting of storage methods in research.