A team of reproductive researchers affiliated with several institutions in France and the US has found that the timing of monthly ovarian cycles is probably attributable to the circadian rhythm, after studying thousands of ovarian cycles reported by women across Europe and America.
Their paper was published in the journal Science Advances.
The timing mechanism behind the ovarian cycle has mystified scientists for centuries, though one of the strongest theories has been that it is tied to the lunar cycle.
Charles Darwin suggested that the two became linked back when humans lived near the seashore, where the tides heavily impacted daily scheduling.
And three years ago a team led by Würzburg chronobiologist Charlotte Förster found evidence for women’s menstrual cycles temporarily synchronising with the cycles of the moon.
In this new effort, reports MedicalXpress, the research team has found little evidence of a lunar impact – they suggest the mechanism most likely controlling the ovarian cycle is the circadian rhythm.
The circadian rhythm is defined as physical, mental and behavioural changes that organisms, like humans, experience over 24-hour cycles.
One of the most famous behaviours affected by the circadian rhythm is sleep – people tend to feel sleepy at the same time every night.
However, it has also been noted that the circadian rhythm can be impacted by the lunar cycle: people have been found to go to bed later and sleep less, for example, on nights before a full moon.
To learn more about the ovarian cycle-controlling mechanism, the research team obtained medical records for more than 3 000 women living in Europe and North America, which held data relating to 27 000 ovarian cycles. The team tracked the first day of each cycle for all of the women under study, and found little correlation between cycle start time and lunar cycling.
The researchers did find something else, though: many examples of what they describe as phase jumps, where something disturbs the timing of a cycle for a given woman, and the body responds by changing the clock rhythm over several months to bring the cycle back to its original norm.
They compare it to how the circadian rhythm reacts to people experiencing jet lag. This, they suggest, indicates that the circadian rhythm is much more likely the mechanism that controls ovarian cycling.
Study details
Evidence that the woman’s ovarian cycle is driven by an internal circamonthly timing system
René Ecochard, John Stanford, Claude Gronfier et al.
Published in Science Advances on 10 April 2024
Abstract
The ovarian cycle has a well-established circa-monthly rhythm, but the mechanisms involved in its regularity are unknown. Is the rhythmicity driven by an endogenous clock-like timer or by other internal or external processes? Here, using two large epidemiological datasets (26,912 cycles from 2303 European women and 4786 cycles from 721 North American women), analysed with time series and circular statistics, we find evidence that the rhythmic characteristics of the menstrual cycle are more likely to be explained by an endogenous clock-like driving mechanism than by any other internal or external process. We also show that the menstrual cycle is weakly but significantly influenced by the 29.5-day lunar cycle and that the phase alignment between the two cycles differs between the European and the North American populations. Given the need to find efficient treatments of subfertility in women, our results should be confirmed in larger populations, and chronobiological approaches to optimise the ovulatory cycle should be evaluated.
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