Circadian Hormone Rhythms
Fundamentals of Endocrinology and Hormones
Circadian Hormone Rhythms
Circadian hormone rhythms are approximately 24-hour patterns generated and coordinated by biological clocks. They interact with sleep, activity and meals, while environmental light helps synchronize the central clock with the external day.
Timing is hormone-specific
Cortisol usually rises toward the biological morning, whereas melatonin increases during the biological night in dim light. Growth hormone release is strongly influenced by sleep and should not be treated as a simple clock-time waveform.
Internal time and clock time
Shift work, travel and irregular schedules can separate biological phase from local time. Two people sampled at the same clock hour may therefore be at different points in their endocrine rhythm.
Practical comparison
When monitoring an athlete, record sleep timing, recent travel and sampling conditions. Repeated tests are more interpretable when relevant conditions are comparable. A change caused by sampling at another biological phase should not be mistaken for a training adaptation or a gland disorder.
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