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Long-term studies on immunoreactive human melatonin.

J Arendt, A Wirz-Justice, J Bradtke

    Annals of Clinical Biochemistry
    |November 1, 1979
    PubMed
    Summary
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    Human melatonin levels show significant variations between individuals at midnight, but not in the morning or afternoon. Seasonal changes also impact melatonin, with higher levels in summer and winter.

    Area of Science:

    • Chronobiology
    • Endocrinology
    • Human Physiology

    Background:

    • Melatonin is a crucial hormone regulating circadian rhythms.
    • Understanding human melatonin secretion patterns is vital for chronobiology research.
    • Previous studies have indicated diurnal and seasonal variations in melatonin.

    Purpose of the Study:

    • To investigate inter-individual and intra-individual variations in immunoreactive melatonin levels in humans.
    • To determine the influence of time of day and season on melatonin concentrations.

    Main Methods:

    • Study involved normal human volunteers (men and women).
    • Melatonin levels were measured at different times of day (0800, 1200, 2400).
    • Seasonal variations were assessed by measuring melatonin at different times of the year.

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    Main Results:

    • Significant inter-individual variability (up to fivefold difference) in mean melatonin levels was observed at 2400, but not at 0800 or 1200.
    • Intra-individual variations showed seasonal effects, with low melatonin in spring/autumn and high levels in summer/winter at 2400 and 0800.

    Conclusions:

    • Human melatonin secretion exhibits substantial inter-individual differences, particularly at midnight.
    • Seasonal fluctuations significantly influence melatonin levels throughout the year, affecting both diurnal and nocturnal concentrations.