ABSTRACT
Background: It has been hypothesized that the yearly menarche rhythm could be caused by the seasonal variation of photoperiod and temperature or by the annual distribution of the scholar vacation and study periods. Aim: To test the hypothesis that the distribution of study vacation periods is a condition that modifies the annual menarche rhythm. Subjects and methods: Two thousand ninety four school girls from Chile, 2.356 girls from Madras, India, 3.454 girls from Medellin, Colombia and 2.627 girls from Debrecen, Hungary, were studied. They were asked about the month of their menarche. Vacation months were considered those with more than 6 days of leave from school. Results: The seasonal hypothesis was refuted because there were contradictions with the expected antithetical behavior in both hemispheres, there was a significant heterogeneity of the yearly menarche among girls from the same region, the expected cline of the menarche frequency variance from equator to poles was not observed, finding an antithetical cline instead and there was a significant heterogeneity among months of the same season. On the other hand, months with vacation periods coincided significantly with peaks of menarche, while study months had lower proportion of menarche (total binomial probability <10-6). Girls whose month of menarche was the same as their month of birth, did not agree completely with the vacation-study hypothesis as the rest of the sample. Conclusions: Vacation periods influenced menarche rhythm. However, these periods coincide with most cultural events and this strong association needs further study to be considered causal. It is not possible to assume school stress as the main explanatory variable. Ontogenetic factors such as birth imprinting also can influence the menarche rhythm, as shown in girls whose month of menarche coincided with their month of birth
Subject(s)
Humans , Female , Adolescent , Menarche/physiology , Child Development , Causality , Photoperiod , HolidaysABSTRACT
Hypotheses on seasonal, phylogenetic and ontogenic factors or imprinting that may produce menarcheal rhythm were tested in a sample of school girls from Medellín, Colombia. The questionnaire included a net of important religious or national feasts and periods of vacation or study to prevent memory biases. Europeanb, Asian and Chilean samples showed peaks of menarche in december and january, but a few samples showed a second in june, july and august. The winter short photoperiod and low temperature were assumed to be the cause of the winter peak in most european samples. However, this seasonal hypothesis was refuted when a chilean sample also showed a peak in december, january and february (summer). In the present study performed in a sample from a tropical country we found 2 peaks of menarche, one in july and the other in november, december and january; thus, the seasonal hypothesis can be hardly supported. Moreover, this sample showed a high coincidence between the month of menarche and the month of birth, and a different pattern of menarche when menarches are distributed according to their coincidence with the gestational development. Both facts affirm the ontogenetic hypothesis, because they were also found in several samples. Since this population is different from those already studied and its monthly distribution of menarches and births is also different from those ones, the hypothetical phylogenetic factors find additional support. The possible influence of school stress and other environmental factors in the menarcheal rhythm are discussed