Seasonal appearance and seasonal disappearance of menstrual function
Maastricht University, Department of Epidemiology, Maastricht, The Netherlands
Email:luc.smits{at}epid.unimaas.nl
Sir,
Garai and co-workers' observation of seasonality in the occurrence of the first missed menstrual bleeding in perimenopausal women (Garai et al., 2004
) indicates that human menstrual function is influenced by seasonally varying environmental factors. As the authors assert, the influence of these seasonal triggers might become stronger from the time that endogenous control of the menstrual cycle starts decaying. In an earlier edition of this journal, we reported evidence pointing to a similar process, though in the reverse direction, at the start of the reproductive span (Smits et al., 1998). In a historical sample of women born at the end of the 19th century, we observed that fecundability (which strongly depends on menstrual function) was higher during late spring and late autumn, and that the strength of the variation depended greatly on age. In women under 20 years of age, fecundability was more than five times as high during these seasons compared with other seasons, while the fecundability of older women (none being older than 39 years) showed a variation of only 40%. Still other authors have described seasonal variation in the timing of menarche, with increased rates during summer and early winter (Brundtland and Liestöl, 1982). Western humans are (virtually) non-seasonal breeders because of, among other things, nutritional abundance, artificial light and artificial heating (Rojanski et al., 1992). At both ends of the female reproductive span, however, the innate propensity of our reproductive system to respond to seasonal cues still shows.
References
Brundtland GH and Liestöl K (1982) Seasonal variations in menarche in Oslo. Ann Hum Biol 9, 35–43.[CrossRef][Web of Science][Medline]
Garai J, Világi S, Répásy I, Koppán M and Bódis J (2004) Short communication: seasonal onset of menopause? Hum Reprod 19, 1666–1667.
Rojanski N, Brzezinski A and Schenker JG (1992) Seasonality in human reproduction: an update. Hum Reprod 7, 735–745.
Smits LJ, Zielhuis GA, Jongbloet PH and Straatman H (1998) Seasonal variation in human fecundability. Hum Reprod 13, 3520–3524.
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