The Moon has always been tied to the rhythms of Earth. It pulls the tides back and forth, and for thousands of years, people have wondered if it also tugs at our bodies.
Do its phases – the waxing glow of a full moon or the dark quiet of a new moon – leave their mark on human life? For centuries, the question sat in the space between myth and science.
Now, researchers have brought new evidence to the table. The study suggests that the human body, particularly the menstrual cycle, may once have been more closely in step with the Moon’s rhythm.
But today, the glow of LED lights and constant screen time may be disrupting that connection.
A weakening connection to the Moon
The team analyzed menstrual records spanning more than 50 years. They found that before 2010, women’s cycles often lined up with the full or new moon.
After 2010, that connection weakened, except for January, when the Moon’s gravitational pull is strongest because of its position with Earth and the sun.
“We show that synchronization with the Moon has decreased significantly since the introduction of LEDs and the increasing use of smartphones and screens of all kinds,” noted Charlotte Förster, a chronobiologist who led the study at Julius-Maximilians-Universität Würzburg.
The scientists believe humans may carry a kind of “moon clock,” similar to those found in marine animals. Many sea creatures time their reproductive cycles with specific moon phases to improve survival.
Humans, too, have menstrual cycles averaging 29.5 days, nearly the same as the lunar cycle. That similarity has long fueled speculation about a natural link.
Moon phases tug at human biology
While the idea of a moon-driven rhythm in humans remains debated, other studies point in the same direction. Basel researcher Christian Cajochen and Washington biologist Horacio de la Iglesia have shown that people tend to sleep less around the full and new moon, no matter if they live in rural areas or bright cities.
“Interestingly, this also applies to city dwellers, where nighttime city lighting is much brighter than the light of the full moon,” said Förster.
Psychiatrist Thomas Wehr discovered that people with bipolar disorder often shift between mania and depression around the full and new moon. These findings suggest the Moon’s cycles may quietly ripple through our biology, even in modern life filled with artificial light.
Artificial light and the Moon connection
According to the Würzburg team, artificial light doesn’t just outshine the Moon – it changes the body’s timing. “However, our study shows that increased exposure to artificial light severely impairs the synchrony between the menstrual cycle and the lunar cycle,” said Förster.
The effect is not only about masking moonlight. Artificial light can shorten menstrual cycles, making it less likely they’ll stay aligned with the moon.
Why does modern light have such a strong effect, when gas lamps and old bulbs have been around for centuries?
“LEDs have much higher energy than gas lanterns and light bulbs. In addition, they have a high proportion of blue light, to which our photoreceptors in the eye are particularly sensitive,” explained Förster.
Blue light – the same kind pouring from phone and computer screens – has an especially powerful influence on our biology.
More questions than answers
Despite the findings, the scientists are cautious. “Our findings show a correlation between these two phenomena. We were unable to establish a causal link,” said Förster.
In other words, the study shows a strong connection, but it can’t prove cause and effect. Still, the work hints at wider implications.
“Since period length appears to be a possible age-dependent marker for female fertility, our findings could be relevant not only for human physiology and behavior, but also for fertility and contraception,” said Förster.
The study is not a medical guide, but it highlights how human biology is still tuned to natural cycles, even as technology interrupts them. The Moon’s quiet rhythm may still be ticking inside us, though smartphones and bright screens make it harder to hear.
The full study was published in the journal Science Advances.
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