Letter to the editor |
Reply to: Comment on ‘Season of birth influences the timing of menopause’
Department of Obstetrics Gynaecology and Paediatric Sciences, Gynaecology Units of Policlinico of 1 Modena, 2 Ferrara and 3 Parma, Italy
4 To whom correspondence should be addressed at: Dipartimento Integrato Materno Infantile, Unità di Ginecologia e Ostetricia, Policlinico di Modena, via del Pozzo 71, 41100, Modena, Italy. E-mail: cagnacci{at}unimore.it
Sir,
The letter of Shukunami and colleagues refers to two papers published almost simultaneously by us on the timing of menopause. The two papers were obtained by the same database. The paper on the seasonal onset of menopause (Cagnacci et al., 2005b
) was written earlier, although published later, and the analysis was performed on 2432 post-menopausal women. The data in this paper indicate that the onset of menopause is not evenly distributed throughout the year, but occurs preferentially in some seasons (in winter and to a lesser degree in summer) compared with others. The data emphasize the important role that environmental factors linked to season play in the regulation of reproductive life including its termination. The paper on the effect of the season of birth on the timing of menopause (Cagnacci et al., 2005a) was written later, although published earlier. Between the two analyses, we were able to retrieve additional information from the paper records of our patients, which were entered into the electronic databases. Accordingly, the analysis was performed in 2822 women. The results indicate that the timing of menopause is influenced by the season in which a woman is born. The data are interesting because they point to the role that prenatal environmental factors exert on postnatal events including a woman’s ovarian exhaustion. Accordingly, the two papers relate to two different and separate issues—the former to season and reproduction, the latter to environment and fetal development. However, we understand the point made by Shukunami and colleagues. It may be that the analysis showing a different timing of menopause on the basis of season of birth is influenced by the seasonal onset of menopause. For example, birth in a season distant from the preferential season for the onset of menopause, may prolong the reproductive period and delay menopause, simply because almost 1 year has to pass before the woman reaches that critical season in which environmental conditions favour the definitive cessation of her menstrual cycles. In order to exclude this possible confounder we re-analysed the data on the season of birth and timing of menopause, taking into consideration also the actual season in which menopause occurred. The additional data included in the database did not modify our previous conclusion (Cagnacci et al., 2005b) that the onset of menopause is more frequent (P < 0.0001) in winter (920/2822, 32.7%) than in spring (583/2822, 20.6%), summer (743/2822, 26.3%; P < 0.001 versus spring and autumn) and autumn (576/2822, 20.4%). In multiple regression analysis this time we tested the influence on the timing of menopause exerted not only by menarche, body mass index, smoking, education, type of job and season of birth, as previously reported (Cagnacci et al., 2005a), but also by season of menopause onset. Timing of menopause remained influenced by season of birth with results comparable to that previously reported (Cagnacci et al., 2005a), and was not influenced by the seasonal onset of menopause. Indeed, considering winter as the season of reference, the influence of the other seasons on the timing of menopause was not significant and expressed by regression coefficients (with 95% interval of confidence) which were 0.270 (–0.187, 0.726) for spring, 0.384 (–0.04, 0.809) for summer and 0.082 (–0.374, 0.539) for autumn. We think that this re-analysis responds to the appropriate criticism of Shukunami and colleagues, and further confirms the genuine effect that the season of birth exerts on the timing of menopause.
References
Cagnacci A, Pansini FS, Bacchi-Modena A, Giulini N, Mollica G, de Aloysio D, Vadora E and Volpe A (2005a) Season of birth influences the timing of menopause. Hum Reprod 20,2190–2193.
Cagnacci A, Pansini FS, Bacchi-Modena A, Giulini N, Mollica G, de Aloysio D, Vadora E and Volpe A, Emilia-Romagna Operative Group for Menopause (GOERM) (2005b) Seasonal onset of menopause. Maturitas 51,393–396.[Medline]
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