Daily patterns of four hormones measured under constant conditions

Melatonin, TSH, and cortisol exhibited clear circadian rhythms during a 36-hour forced wakefulness period.

• Subjects were four healthy men aged 22-24 years.
• Blood samples were taken hourly while food and water were provided bi-hourly.
• Melatonin, thyroid stimulating hormone (TSH), and cortisol showed distinct circadian patterns even without physical exercise.
• Growth hormone (GH) secretion did not appear to be entirely regulated by the circadian rhythm.
• The suppression of GH around body temperature nadir suggests some level of circadian modulation.

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