Circadian rhythms of 6-sulphatoxy melatonin, cortisol and electrolyte excretion at the summer and winter solstices in normal men and women

Abstract

Abstract. Urinary excretion of 6-suphatoxy melatonin, cortisol, potassium and sodium was monitored at four hourly intervals for 24 h in 30 normal subjects at the summer and winter solstices. The 24 h profiles were fitted to sine curves and mean 24-h excretion, time of maximum excretion and amplitude of the curves compared. The excretion of 6-sulphatoxy melatonin was remarkably stable at the two times of the year (24-h excretion 108 ± 6.3 nmol in summer and 105 ± 6.3 nmol in winter, mean ± sem). The time of maximum excretion was significantly delayed in winter by 1 h and 40 min. Urinary cortisol excretion was significantly higher in winter, however, the amplitude was unaltered. The time of maximum excretion of cortisol was significantly delayed by 1 h and 34 min. Potassium and sodium excretion were both unaffected by seasonal influences. These results contrast with results in some animal species in which the duration of the melatonin signal is thought to be the key determinant in subsequent melatonin action. In humans it is likely that the phasing of the melatonin rhythm is of prime importance.

Individual Variations in Serum Melatonin Levels through Time: Implications for Epidemiologic Studies

“…During the winter, melatonin circadian rhythm also displays a phase shift towards the morning hours [63], [64], [66], [67], [86]–[88], with shorter duration of melatonin excretion [79] which could attenuate seasonal differences in melatonin levels if samples are collected in the morning, as they were in our study.…”

A week in the life of full-time office workers: Work day and weekend light exposure in summer and winter

“…In this study, despite some differences in light exposure between seasons, the timing of the DLMO at the end of the working week did not differ between summer and winter. Other studies have reported a delayed melatonin phase in winter compared to summer, but again these were studies of people with presumably more flexible schedules than full-time office workers (Honma et al, 1992; Illnerova et al, 1985; Kennaway and Royles, 1986). The timing of the DLMO significantly correlated with the first exposure to 10 lux, which occurred shortly after waking indoors.…”

Bimodal rhythms of general conceptions and the birth-month phenomenon in schizophrenia, neural tube defects, and laterality: A solstitial hypothesis

“…This hypothesis of diminishing sunlight exposure is supported by studies of blood melatonin, the nighttime hormone whose secretion by the pineal gland should be inversely related to day length. Several studies conducted around the 1980s failed to find an annual rhythm in the blood levels of melatonin among normal, urbanized American or European subjects (Illnerová et al,1985; Kennaway and Royles,1986; Wehr et al,1995). This was explained in the latter study in terms of artificial lighting suppressing the normal response to the natural photoperiod.…”