Night of the living: A new study shows that people undergoing heart surgery have a lower death rate if their operation is done when the moon is starting to wane
For thousands of years, people feared the moon could change us into werewolves or even mermaids.
These days, alternative health gurus sell calendars that show the 'best' lunar phase for losing weight (supposedly a waning moon - one that is getting smaller in the sky) or using face packs (a waxing moon - which is getting larger).
Such ideas may seem scientifically laughable. But might there be something in them?
Last week, U.S. surgeons reported that people undergoing heart surgery have a lower death rate if their operation is done when the moon is starting to wane.
The study at Rhode Island Hospital followed 210 patients who'd undergone surgery between January 1996 and December 2011 to repair life-threatening tears in the lining of the aorta, a rare condition known as aortic dissection.
Dr Frank Sellke, the lead researcher and chief cardiothoracic surgeon, says: 'We found the odds of dying following the procedure were greatly reduced during the waning full moon, and that length of stay was also reduced during the full moon.'
Indeed, people who had the surgery during a full moon stayed in hospital for an average of ten days, compared with 14 for those who underwent it at other times in the lunar cycle, according to a report in the journal Interactive Cardiovascular and Thoracic Surgery.
This kind of lunar influence - also known as the 'Transylvania effect' - has long caused rows among medical experts. Does the moon really affect our bodies, or is such evidence is merely the result of coincidences and statistical quirks?
A report in April's European Journal of Preventive Cardiology seems to support the moon-believers. As with the Rhode Island study, it found that the waning moon just after a full moon may protect people's hearts.
The researchers, from the Central Hospital of Augsburg, Germany, studied the records of 16,000 heart-attack victims, and also found significantly fewer attacks occurred in the three days after a new moon.
Some experts believe this may be caused by the moon's gravitational pull affecting heart functions. When the moon is full, and at new moons (when the sun and moon are aligned), the gravitational pull of the moon and sun are combined, and gravity is thought to be at its strongest. The idea is that this may have the most beneficial effect on human circulation at or just after a full moon.
Evidence for this effect has also been found in India by researchers at Vidyasagar University. They asked 80 students to do exercises every day for a month while having their heart rate, blood pressure and athletic performance monitored.
The 'Transylvania effect': Some experts believe the moon's gravitational pull affects heart functions
The results suggested that at full moons, people's cardiovascular systems were working at their most efficient rates, reported the International Journal of Biometeorology last November.
Some medics also believe that the moon's gravitational pull can affect the flow of fluid in the human body. If this is the case, then it should prompt kidney-stone trouble at times when the moon's pull is strongest - at full moons and new moons.
One study, in the journal Emergency Medicine International, found that hospital admissions for kidney stones didn't vary according to lunar cycles.
However, other research suggests the opposite. In 2011, the Urology Journal published evidence from a study of nearly 1,500 patients that renal colic - pain commonly caused by kidney stones - seemed to increase significantly at the time of the full moon.
Furthermore, a study at the Royal Liverpool University Hospital in 2008 found that emergency urological admissions did seem to be affected by lunar phases.
'Emergency urological admissions were higher on full-moon days,' said lead researcher Hasan Qazi in the journal Current Urology. 'The new moon had a calming effect.'
The pull of gravity may also make a difference to other fluids in our bodies - even our brains - according to Dutch researchers. Their study of more than 5,400 patients in 2011 showed that emergency admissions of psychiatric patients rose during full- moon periods.
The researchers, from Radboud University, Nijmegen, suggest this may be caused by the moon's gravity affecting the flow of fluids in the brain - and in individual brain cells - which in turn may alter people's mood and behaviour.
Controversial findings: Results from this study suggest that at full moons, people's cardiovascular systems were working at their most efficient rates
The effect of the moon on patients' health has also been noted by GPs. In a study published in the doctors' newspaper Pulse, Dr Peter Perkins, a GP in Bournemouth, interviewed 79 general practitioners and found that emergency calls for all conditions increased by 3 per cent at full moon and dropped by 6 per cent during a new moon.
Similar research at Leeds University has found that GP consultation rates rise by 3.6 per cent during a full moon. Many experts remain highly sceptical, however. Numerous studies have found no influence in areas where the moon was thought to have power. For example, the moon may have been worshipped in ancient times as the goddess of fertility and delivery, but there seems to be no link between its phases and the rates of childbirth.
This was the conclusion of a study of 13,000 births by Brazil's University of Sao Paulo, published in the International Journal of Biometereology last July, which investigated whether this phenomenon existed.
Some German scientists seem particularly keen to debunk the idea of lunar influence. Surveys in Germany show that more than one in ten people are convinced that the moon affects their health, and lunar calendars with recommendations for daily life have become increasingly popular there.
Some people have claimed that the lunar phase may produce more beneficial outcomes in other surgery, such as hip replacements, but German statistical research so far has shown there's no link.
But even if we accept that the moon has an effect, this may not be due only to the moon's gravitational pull, argue some scientists. Rather, the effect might be due to the way the moon's proximity distorts the Earth's magnetic field.
However, sceptics say that such effects are tiny compared with our home environment, which is full of magnets.
Perhaps lunar influence could also come down to something simpler than invisible forces. It might be caused by changes in natural levels of light. The full moon's light is up to 16 times greater than at other lunar phases.
Researchers at University College London have discovered that the number of epileptic seizures, which are related to electrical activity in the brain, falls when the moon is at its brightest.
'These findings suggest that epileptic seizures are less likely to occur on brighter nights,' says Dr Sallie Baxendale from the Institute of Neurology, who led the study. She believes the hormone melatonin, secreted only at night and in the dark, might be implicated, although it is not clear how.
So far, all these research efforts leave us with more tantalising questions than answers. And, as Dr Sellke, author of the latest research, has asked, even if we do prove that the moon has a medical influence, what should we do with that knowledge?
While it may help some people with epilepsy to reduce their risk of fits on certain nights, it would cause widespread chaos if hospitals cancelled all surgical operations on nights when the lunar phase appeared statistically unhelpful.
Anyone who suggested such a thing might be dismissed as moonstruck, or justifiably labelled a complete lunatic.
