Hair analysis is increasingly utilized in psychoneuroendocrine research to assess long-term hormonal activity. A critical practical question when using this method is how long hair samples can be stored without compromising data quality, yet this issue remains insufficiently researched. Here, we report data from a first systematic, well-controlled within-subject investigation into the impact of storage duration (over 12 months) on hair cortisol and other common hair analytes. Participants (N = 81) provided hair samples from the posterior vertex, which were divided into aliquots and analyzed either (i) immediately or after standardized storage (dark, dry, at room temperature) for (ii) 3, (iii) 6 or (iv) 12 months. To prevent confounding by laboratory batch effects, recruitment and initial hair sampling were conducted in four sequential waves (starting at three-month intervals), so that influences of storage duration and analytical cycle were independent of each other. Concentrations of steroid hormones (cortisol, cortisone, progesterone, dehydroepiandrosterone) and endocannabinoids (AEA, 1/2-AG, OEA, SEA, PEA) in the proximal 3 cm hair segment were quantified via LC-MS/MS. Significant decreases in concentrations after 12 months of storage were observed for hair cortisol (-28.0 %) and cortisone (-23.7 %), progesterone (-43.9 %), OEA (-33.8 %) and 1/2-AG (-69.9 %). Importantly, significant declines were already evident after six months for cortisol, cortisone, OEA and 1/2-AG and even after three months for progesterone. Further, longer storage durations were associated with reduced analyte stability, reflected in weaker correlation strengths between initial and delayed analyses. Our findings demonstrate that extended storage duration adversely affects the quality of results for hair cortisol and cortisone as well as for other hair steroid and endocannabinoid analytes. Therefore, storage duration should be considered as a critical methodological factor when planning the study design and interpreting hair data. Analyzing hair samples within six months post sampling is recommended. Further, details on storage methods should be transparently reported in future research.
Huthsteiner et al. (Mon,) studied this question.