Adaptation of the circadian rhythm of 6-sulphatoxymelatonin to a shift schedule of seven nights followed by seven days in offshore oil installation workers

This study evaluated circadian adaptation in a 'swing shift' schedule (seven nights, 18:00-06:00 h; then 7 days, 06:0018:00 h) on North Sea oil installations. Eleven healthy men provided sequential urine collections for the study period offshore. The urinary melatonin metabolite 6-sulphatoxymelatonin (aMT6s) was used as an index of circadian phase. A significant difference (P = 0.0004) was found between the mean aMT6s acrophase (calculated peak time) at the start (+/-SD: 05:34 +/- 2.42 h) and end ( +/-SD: 10.95 +/- 3.34 h) of the night shift week, but not between the start ( +/-SD: 11:04 +/- 4.03 h) and end ( +/-SD: 12:59 +/- 8.83 h) of the day shift week. As a group, the subjects adapted to the night shift but very large individual variations were seen during the day shift. These individual differences clearly require further study. 0 2002 Published by Elsevier Science Ireland Ltd.