Fertility researchers in Hungary have revealed that the onset of menopause may not only be dictated by the fact that a woman's lifetime supply of eggs is running low, but also by changes in the seasons. The research was published in the journal Human Reproduction.
Analysis of questionnaires from patients at the menopause clinic at Baranya County Teaching Hospital in Pécs, revealed that the spring and autumn equinoxes played a conspicuous role in the timing of the menopause.
"We found that there was a high peak after the spring equinox and another, lower one, after the autumn equinox," said research leader Dr János Garai.
Of the 102 women whose questionnaires were analysed, 72 remembered the exact month that their menstrual periods stopped, while 30 could recall only the season.
Dr Garai said, "Seasonal variations of reproductive functions in wild animals are well known, and similar but not so definite seasonal trends have been described for humans. The menopause is a complex set of symptoms that we know is determined partly by external and partly by internal influences, but there are only scarce data about the exact nature of environmental and/or lifestyle determinants.
So we wanted to find out more in the hope that this might help in the future in implementing innovative approaches to treating problems in the menopause. The seasonality we found seems to support the influence of environmental factors on female human reproductive functions even when they are declining. The pattern of the peaks following the equinoxes appears to be similar to the bimodal distribution of conceptions in Eastern Europe."
The questionnaires recorded responses to a wide range of lifestyle and environmental factors and Dr Garai said that it was the sequence of seasons that seemed most obviously to affect the process leading to the menopause.
The authors of the report say that the triggering factors and the mediators involved need further research. However, melatonin, a hormone secreted by the pituitary gland, which is generally accepted to play a role in the circadian rhythm (the 24 hour time clock that governs different physiological processes), could be involved. Melatonin binding is found in the ovaries and it also influences ovarian steroid hormone production. Other research has shown that the harmony of these links becomes disrupted in parallel with a fall in melatonin levels in early peri-menopause.
"The cessation of ovarian function is a process from regular towards irregular control," said Dr Garai. "What we already know, coupled with our new findings, mean it is plausible that this process is not just due to the ovaries no longer being able to produce developing egg follicles that provide an adequate hormone supply. Rather, it can be perceived as the ovaries - governed by several internal and external factors affected by climatic conditions such as length of day, temperature and humidity - losing their ability for cyclic renewal.
"Because of the imbalance of these factors in pre-menopause, the process eventually culminates in a point where it stumbles into irrecoverable ovarian failure. Length of day is likely to be only one of several factors operating and melatonin might not be the only agent involved so we need to research this further."
Dr Garai said that seasonality of one aspect (the first missed bleed) of the complex chain of events might indicate that other events could also be affected by the seasons. For example, hot flushes occur more frequently in summer (for obvious reasons). But, not all women have hot flushes. "No one has ever looked into whether the time of first missed bleeding shows any correlation with the severity or the frequency of hot flushes, or with the proportion of women who have them. Gaining more in depth knowledge might eventually lead to more efficient ways of dealing with menopausal problems."