Despite a national love of the coffee bean, scientists are still collating evidence on whether caffeine harms or helps our health. Only last week, US researchers revealed that expectant mums who drink two cups of coffee a day are twice as likely to miscarry than those who don’t drink any.

Studies of the effect of caffeine on Parkinson’s disease and cognitive decline are fascinating because they suggest that caffeine acts differently in men and women. This raises the possibility that caffeine interacts with sex hormones. Women who suffer from premenstrual syndrome (PMS) are often advised to cut out caffeine, but the medical literature throws up no conclusive evidence of a link between caffeine and PMS.

Before exploring that possible link, let’s look at the Parkinson’s research. Several large studies have shown that male coffee drinkers – but not female – lower their risk of Parkinson’s. In 2003, researchers at the Harvard School of Public Health investigated why the protective effects of caffeine were confined to men. “We hoped to find something that would explain it,” Dr Alberto Ascherio says. “Hormones seemed a possible factor in this case.”

What they also found was that when women either drank coffee or took hormone replacement therapy, their risk of Parkinson’s fell. But when they did both, the risk rose. Dr Karen Ritchie, at the French National Institute of Health and Medical Research (Inserm) Montpellier, notes that at least one previous animal study “suggests there’s an interaction between caffeine and the female sex hormones estrogen and progesterone”. Thankfully for women, the benefits of caffeine do not all lie on the male side. A French study carried out by Ritchie and published recently in Neurology noted that coffee could protect against mental decline in older women, but not in older men. This again has fuelled speculation that caffeine and sex hormones are somehow acting in concert. In the study 7,000 over65s were recruited and given cognitive tests in a four-year period. Women who drank three or more cups of coffee a day were less likely to see their mental acuity fall over that period. That finding was not replicated in men.

Moreover, among female coffee drinkers, the beneficial effects were especially seen in older participants (the over80s). Ritchie speculates that caffeine and estrogen home in on the same receptors in the body. Older women have less estrogen – therefore, more receptors are available for the caffeine to latch on to. One would deduce that caffeine would have a greater effect in this population, which here translates, happily, into reduced mental decline.

The exact link between hormones and caffeine remains a mystery, but rumours of a link between PMS and caffeine persist. Zoe Wheeldon, from the British Coffee Association, says that there is no conclusive evidence to either prove or disprove the theory that PMS symptoms are worsened by coffee, but caffeine can have differing effects on people. “We can give general advice only, which is that four or five cups a day is safe. But people can metabolise caffeine differently. People should do what suits them.” Wheeldon says that a woman embarking on this course, if she is used to a few more cups a day, should replace the fluid in other ways to avoid dehydration.

Nigel Denby, a registered dietician who runs a women’s health clinic at Queen Charlotte’s Hospital, which is affiliated with Hammersmith Hospital, West London, regularly sees women with hormone-related conditions, including severe PMS. He estimates that half of his PMS patients, are adversely affected by caffeine. “I don’t think caffeine itself causes PMS, but in some women the stimulant effect of caffeine may exacerbate symptoms,” Denby says. He has noticed that certain symptoms – insomnia, tearfulness, irritability, mood swings, headaches – appear to be worsened by caffeine. “The problem with giving general advice is that women differ so much in their sensitivity to caffeine. If your intake is two cups of weak filter coffee a day, you might be affected more than someone who drinks double espressos throughout the day.”

For this reason, Denby does not believe that caffeine elimination should be generally advised: “I would not include it as a blanket rule. I might suggest that someone who has four cups a day cuts down to two or three.”

Denby, like Wheeldon, also stresses the importance of replacing the fluid lost when coffee intake falls. It is especially important for PMS sufferers who experience fluid retention. Instead of cutting down fluids, Denby says, it is important to keep drinking to ensure the kidneys are working properly.

His basic advice is that women should do what works for them: “If you come out in a rash after drinking coffee, then you probably are sensitive to caffeine. What I’d say is, there’s no harm in trying to cut down caffeine to see if it improves things.”

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