Scalp hair samples were collected from ~59,000 adult participants during 2A Visit 2. The main aim of hair collection was to use the samples for the assessment of hormone levels, e.g. cortisol (section:physical state).

Cortisol levels are typically assessed in serum, saliva, or urine samples. However, due to the circadian rhythm of cortisol, its pulsatile secretion, and the daily variation due to changing circumstances like acute stress, these samples provide non-representative snapshots of chronic cortisol levels in the human body. For that reason, a novel non-invasive parameter to measure cortisol using scalp hair was developed ¹⁾, providing the unique opportunity to measure long-term cortisol levels that reflect the mean levels of several months (since hair grows with an average of 1 cm per month). Using this technique, it is now possible to study chronic cortisol levels over time in very large cohorts ²⁾.

During 2A visit 2, participants were asked to provide a lock of hair. Nurse practitioners that assisted in the visit cut off a lock of hair close to the scalp using clean scissors. The lock of hair was placed in an envelope, clearly marked and registered, and stored at room temperature.
Participants also filled in a questionnaire about their hair. See the list of quesitons below.

1. Wester et al. (2017) Hair analysis reveals subtle HPA axis suppression associated with use of local corticosteroids: The Lifelines cohort study. Psychoneuroendocrinology 80: 1-6
2. van Manen et al. (2019) Scalp hair cortisol and testosterone levels in patients with sarcoidosis. Plos ONE 14(6): e0215763
3. Savas et al. (2019) Hair glucocorticoids as biomarker for endogenous Cushing's syndrome: validation in two independent cohorts. Neuroendocrinology 109(2):171-178