0078 INTER- AND INTRA-INDIVIDUAL RELATIONSHIPS BETWEEN PLASMA AND SALIVARY MELATONIN AND URINARY AMT6S

Abstract Introduction: Plasma melatonin is widely regarded as the gold-standard marker of circadian phase. Salivary melatonin and urinary 6-sulphatoxymelatonin (aMT6s) are also often used as circadian markers when a non-invasive approach is required, particularly in field settings. Few studies to date, however, have examined the inter- and intra-individual temporal relationships between plasma and salivary melatonin and urinary aMT6s. We aimed to quantify the temporal associations between the different melatonin phase markers under controlled laboratory conditions. Methods: Eighteen participants (25.5 ± 6.2 years, 13 males) underwent a 40 hour constant routine. Blood and saliva samples were collected hourly, and urine samples collected every 2 to 4 hours. Melatonin and aMT6s was determined by radioimmunoassay. Plasma and salivary dim light melatonin onset (DLMO; cut off: 5 pg/ml) timing was calculated, and urinary aMT6s profiles were subjected to cosinor analyses to determine aMT6s acrophase (peak) timing. Results: Overall, plasma and salivary DLMO occurred at 21:09 ± 01:17 h and 21:42 ± 01:26 h, respectively. Urinary aMT6s acrophase occurred on average at 03:48 ± 01:00 h. Within individuals, plasma and salivary DLMO were highly correlated (r=0.95, p