Summary
Hormone levels follow daily cycles, with cortisol peaking in the morning and melatonin at night.
In depth
Cortisol peaks near waking, growth hormone during sleep, melatonin at night, testosterone in the morning. Shift work disturbs hormone rhythms. Chronotherapy times medicines to rhythms.
Clock genes regulate hormone secretion. Meal and light timing entrain peripheral clocks. Disruption affects metabolism and fertility.
Example: cortisol peaks at about 8 am.
Hormone secretion follows daily rhythms organised by the suprachiasmatic nucleus and peripheral clocks. Cortisol peaks shortly after waking (the cortisol awakening response) and falls to a minimum around midnight; melatonin rises at night; growth hormone surges in early deep sleep; TSH peaks at night; testosterone is highest in the morning.
Insulin sensitivity and leptin also vary with time. Disrupted rhythms, as in shift work, jet lag, irregular meals or light at night, are linked to metabolic disease, mood disorders and reduced fertility. Timing of hormone replacement can match natural rhythms, and blood samples for tests such as cortisol must be taken at defined times.
Example: hydrocortisone doses are often given larger in the morning.
Key idea: when a hormone is measured matters.
Frequently asked questions
What is Circadian Endocrinology?
Hormone levels follow daily cycles, with cortisol peaking in the morning and melatonin at night.
Which area of biology covers Circadian Endocrinology, and how advanced is it?
Circadian Endocrinology is one of the 54 topics in Reproduction & Endocrinology. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Melatonin, Endocrine Disruptors, Hormones.
Can you give an example of Circadian Endocrinology?
Cortisol awakening response.
What should I learn before Circadian Endocrinology?
Work through the Beginner topics in Reproduction & Endocrinology first, such as Reproduction, Asexual Reproduction, Sexual Reproduction, then return to Circadian Endocrinology. Advanced topics assume the Intermediate vocabulary.
What topics are related to Circadian Endocrinology?
The closest topics to Circadian Endocrinology are Melatonin, Endocrine Disruptors, Hormones, Pregnancy Hormones. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Circadian Endocrinology?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Circadian Endocrinology. To practise the whole of Reproduction & Endocrinology, use the Reproduction & Endocrinology quiz.
How is Circadian Endocrinology different from Melatonin?
Circadian Endocrinology: Hormone levels follow daily cycles, with cortisol peaking in the morning and melatonin at night. Melatonin: A pineal hormone that signals darkness and helps regulate sleep timing. Read both side by side and note what each one explains.
How should I study Circadian Endocrinology step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Melatonin and explain the difference aloud. Finally, take the Reproduction & Endocrinology quiz and come back to this page for any question you miss.