"Melatonin, menstruation, and the moon"

Townsend Letter for Doctors and Patients, Feb-March, 2005 by Sari Cohen

Introduction

The relationship between the moon's cycles and menses is so fundamental that the two phenomena are related linguistically. The terms 'moon' and 'menstruation' share the same Latin or Greek root, m-, meaning 'to measure.' Various world religions and cultures have acknowledged the bond between women and the moon. Traditional Chinese Medicine links the moon with the feminine, or yin principle. Jewish tradition dictates that women should celebrate Rosh Chodesh, the new moon. Many cultures have assigned the moon a goddess, from Babylonian Ishtar to Greek Artemis. This connection endures today with religious, spiritual, and even health practices. Herbalist Rosemary Gladstar writes that "all the fluid energy of the earth responds to the moon cycles" and advises her amenorrheic patients to pay attention to the lunar cycle as an adjunct to herbal therapy to regulate menstruation. (1) Although it is clear that the menstrual cycle lasts more or less as long as the lunar cycle, the reason why such a relationship should exist is not so obvious.

The pineal gland may provide one possible connection between the lunar and menstrual cycles. The pineal gland and its main secretory hormone, melatonin, are shrouded in mystery. The exact role of this gland has eluded scientists to this day. The ancient Greeks and later Rene Descartes, the 17th cantury French philosopher and mathematician, described the pineal as "the seat of the soul." The "third eye" of Eastern religions is associated with the pineal gland. Greenspan and Gardner, in their textbook Basic and Clinical Endocrinology write that "the physiologic roles of the pineal remain to be elucidated, but they involve regulation of gonadal function and development and chronobiologic rhythms." (2)

The pineal gland secretes melatonin and also contains TRH, somatostatin, GnRH, and norepinephrine. Melatonin, also called N-Acetyl-5-methoxy-tryptamine, is a derivative of tryptophan. The pineal releases melatonin into cerebrospinal fluid and into general circulation. Melatonin secretion increases in response to darkness and hypoglycemia. This primarily nocturnal hormone is well known for its sleep-inducing abilities and its role in the circadian rhythm. Murray and Pizzorno report that it also possesses antioxidant effects. (3) Other important functions include anti-tumor and anti-aging activity.

Less understood is melatonin's role in reproductive function, namely its actions on the menstrual cycle. This paper will explore the intricate relationship between melatonin, the female sex hormones, prolactin, and the lunar cycle. We know that the menstrual cycle and lunar cycle coincide and that the pineal gland is sensitive to light exposure and is related to gonadal function. Are these processes linked in some way? In a preliminary search of scientific literature for research and articles on the pineal gland, melatonin, menstruation, and lunar cycles, a number of intriguing facts surface. Analysis of this data leads me to propose that the moon influences the menstrual cycle through (possibly vestigial) interactions between lunar light exposure and melatonin release. These propositions are not explicitly proven in studies due to the lack of research in this area. The aim of this paper is simply to point out the potential implications of various research studies, combining physiology, folk wisdom, and common sense to explain and explore the moon's effects on the menstrual cycle.

Melatonin and Menses

There is a direct correlation between melatonin and the menstrual cycle. Three studies report that melatonin reaches its zenith during menstruation and its nadir during ovulation. (4) Research by Cagnacci et al. found that melatonin enhances LH in the luteal phase and acts with progesterone to attenuate the core body temperature. (5) In their paper "Melatonin and its role in human reproduction," Wojtowicz and Jakiel state that melatonin is likely essential in both folliculogenesis and spermatogenesis. (6) Melatonin may affect the female hormones and thereby help regulate the menstrual cycle via its relationship with prolactin. The nightly melatonin surge is followed by a surge in prolactin. (7) Prolactin is one of six hormones secreted by the anterior pituitary. Prolactin stimulates lactation in postpartum women and breast development in pregnant women, but otherwise its role in physiologic gonadal function is unclear. The pathological state of hyperprolactinemia is associated with suppressed gonadal function: anovulation, a menorrhea, and infertility. Prolactin appears to decrease the pulsatile secretion of FSH and LH without affecting these hormones' basal levels. Prolactin also suppresses the midcycle surge of LH. (8) This suppression would effectively inhibit ovulation. In one Japanese study by Miyauchi et al., women in the follicular phase of their cycles were exposed to light during various hours of the night and their serum levels of melatonin, prolactin, FSH, and LH were then measured. Melatonin and prolactin were decreased while FSH levels increased. (9) These levels mirror the findings mentioned previously, that melatonin is higher in the follicular phase and decreased in the luteal phase of the menstrual cycle. The role of melatonin in the menstrual cycle may therefore be an indirect one: melatonin is linked with prolactin release, which then acts on female sex hormones.