New studies shows why that time of the month makes women more tempted to stray due to their level of hormones while on their periods .
woman’s hormones may be a source of cheap jokes, but the fact is hormones do have a very powerful effect on how a woman behaves throughout the month.
Just this week a study found that women eat almost 500 calories extra a day in the run up to their periods.
It’s thought this is due to a change in hormone levels which has the effect of making sweet foods and carbohydrates more appealing.
As levels fluctuate at different stages of the cycle, mental tasks can become more or less challenging, for instance.
Scientists recently revealed that women become smarter just before their period, due to part of the brain growing.
‘Many women are more rational and controlled after ovulation,’ says Karen Pine, a professor of psychology at the University of Hertfordshire.
‘But they then experience a rise in impulsive behaviour, anxiety and irritability during the next phase, when they are pre-menstrual.’
Here, leading experts reveal the latest thinking about how different times in a woman’s cycle can affect her body and behaviour…
Day one of a woman’s period is the first day of the cycle.
This is the start of the follicular phase, during which time follicles form on the ovary, one of which will mature into an egg, and lasts for about ten to 14 days until ovulation (when an egg is released, ready for conception).
During the follicular phase, the hormone oestradiol (a type of oestrogen) begins to rise, explains Dr Neave.
Oestrogen is important for preparing the egg for ovulation.
But it’s also linked to positive moods, motivation, memory, reduced anxiety and may also help contain stress levels, helping to keep moods stable.
Rising levels of oestrogen also help to increase libido, which peaks around ovulation.
As a result, this first part of the cycle is the time of the month when most women are at their happiest, adds Dr Virginia Beckett, a spokesperson for the Royal College of Obstetricians and Gynaecologists, who is based in Bradford.
Several studies have shown that women feel more attractive as they approach ovulation — perhaps because it’s nature’s way of encouraging women to have sex during their most fertile time.
Meanwhile their voices rise in pitch (to make them sound more feminine, research suggests), their body odour becomes more sexually attractive (to attract a mate) and they may wear less clothing.
‘Body temperature goes up slightly — because metabolic rate increases slightly — so women may not need to wear as many clothes,’ explains Dr Beckett.
In fact, many ovulation tests use body temperature as a gauge of where a woman is in her cycle.
In an infamous study from 2007, professional exotic dancers were asked to keep a record of their nightly tip earnings for two months.
The women also reported when their periods began and ended, so researchers could calculate when they were most fertile.
Dancers received about £42 per hour when they were near ovulation, but only £33 at less fertile times of the month and £23 while menstruating.
After the follicular phase comes ovulation — the single moment when the egg is released from the ovary.
After this, it only lives for 24 hours — however, sperm can live up to for three days, so if there’s sperm around and an egg floats by, it’s still possible to conceive even if the woman hasn’t had sex on the day of ovulation.
Women are at peak fertility around ovulation, and this is the time they are more likely to adapt their dress style to impress men, says Professor Pine. ‘It’s known as the ornamentation effect.’
This is because females are biologically programmed at this time to prove they are ‘more desirable than the rest of the pack’.
Indeed, a study published in the Journal of Consumer Psychology in 2010 found women are more likely during ovulation to buy clothes, make-up, and other items to boost their attractiveness.
‘Buying a status item is a clear indicator we are at our peak of fertility,’ says Professor Pine, explaining why women are more likely to splash out on something like an expensive bag or pair of shoes at this time.
Women are also twice as likely to engage in extra-marital behaviour around the time of ovulation, adds Professor Pine.
Scientists at the University of Aberdeen and the University of St Andrews found that when progesterone levels are raised during the second half of the menstrual cycle (when the body is preparing for pregnancy) women become more committed to their romantic partners.
But when progesterone is low — in the first part of the cycle before ovulation — women are drawn to masculinity and more likely to have an affair.
Not only that, women may also have better brain function when they are at their most fertile.
Last month, researchers from the Max Planck Institute for Human Cognitive and Brain Sciences in Germany revealed that the hippocampus — the brain area where memories are first formed and which has a key role in emotions — ‘grows’ as oestrogen levels rise.
But as oestrogen levels drop following ovulation as her body prepares for menstruation, this area of a woman’s brain shrinks, MRI scans revealed.
The growth in size and later shrinkage happen ‘with astonishing regularity’ the researchers wrote in the journal Nature Scientific Reports, but more research is needed to establish why.
The stage of a women’s menstrual cycle can even affect how likely a woman is to become addicted to prescription medication such as opioid painkillers.
Scientists at Davidson College, North Carolina found that levels of addictive cravings fluctuated throughout a woman’s cycle.
After ovulation, a woman enters the second stage of her cycle, called the luteal phase.
This lasts, on average, between 11 and 13 days, until her period starts, and is widely considered a more emotionally difficult time.
The main reason is the empty follicle that once contained the egg triggers the release of another hormone, progesterone, says Dr Neave.
This helps to thicken the lining of the uterus and prepare it in case an embryo is implanted.
But this burst of progesterone is associated with negative mood, which is why, coupled with a decline in oestrogen, so many women feel low in the second part of their cycle, particularly by the end of it when pre-menstrual tension often strikes.
When progesterone is high, in the second half of the cycle, the two sides of the brain become ‘decoupled’, says Dr Neave.
This results in confusion, mood swings, problems finding words and a lack of sharpness.
‘Women also seem to be affected by a lack of oestrogen at this stage, too,’ he says.
‘Part of the brain involved with higher cognitive ability, the prefrontal cortex, responsible for organisation, planning and memory processing, suffers.’
As a result, a woman may walk into a room and forget what she went there for, he adds.
Research by Professor Pine found that women are significantly less controlled and more impulsive with money in the ten days before their periods begin.
‘The later women were in their menstrual cycle, the more likely they were to have overspent,’ she says.
This could be because a shopping spree helps deal with the intense emotions of pre-menstrual tension.
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