Endogenous Circadian Regulation of Female Reproductive Hormones.
Level 4 - case-series / case-control
Within-subject laboratory physiological study without a separate control group
PubMed 31415086 · doi:10.1210/jc.2019-00803
What was done
Seventeen healthy premenopausal women (mean age 22.8 ± 2.6 years; 9 follicular phase, 8 luteal phase) were monitored across approximately 90 consecutive hours in an intensive physiological monitoring unit. The protocol consisted of 2 baseline days under a standard sleep-wake schedule followed by approximately 50 hours of extended wakefulness under constant routine conditions to eliminate external time cues. Plasma estradiol, progesterone, LH, FSH, SHBG, melatonin, and core body temperature were measured from serial blood samples.
What was found
All measured hormones (estradiol, progesterone, LH, FSH, SHBG) showed significant 24-hour rhythms under both standard sleep-wake and constant routine conditions during the follicular phase (P < 0.05). In the luteal phase, only FSH and SHBG maintained statistically significant 24-hour rhythmicity. Rhythm acrophases and amplitudes were similar between standard sleep-wake and constant routine conditions, with peak times occurring in the morning for progesterone, in the afternoon for FSH, LH, and SHBG, and during the night for estradiol.
Why it matters
This study demonstrates that 24-hour rhythms in circulating female reproductive hormones are driven by endogenous circadian regulation rather than external behaviors or sleep-wake cycles, clarifying how circadian disruption may directly influence reproductive biology.
Limits
The sample size was small (17 total; 9 follicular, 8 luteal) and restricted to healthy young premenopausal women in a short-term laboratory setting. Exact numerical baseline values, rhythm amplitudes, and confidence intervals were not reported in the abstract.
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