As more and more coffee outlets open Ed Power asks what our growing caffeine habit is doing for our health
Tea may be Ireland's most popular drink, but coffee is its favourite fuel. For thousands of us, a dose of caffeine every morning is an essential kick-start to the day. Coffee helps us shake off fatigue and confront the world head on.
With coffee shops opening on every street corner and reports that the US's favourite coffee chain, Starbucks, is on its way to Dublin this appears to be no passing fad. But could Ireland's love affair with the brew have long-term health consequences?
Research on the beneficial and harmful effects of coffee is complex and often contradictory. Some studies indicate that a moderate caffeine habit of four or less cups a day helps combat heart disease; others highlight the substance's (moderately) addictive qualities and warn that, over the course of years, it can lead to high blood pressure.
The reason many of us drink coffee of course is for its stimulative properties. Researchers have found that coffee boosts our short-term recall and temporarily raises IQ. It also changes the metabolism of a person so that their body burns a higher proportion of lipids to carbohydrates, which can help avoid muscle fatigue.
However, consuming too much coffee at once may lead to "caffeine jitters" a nervous condition typically accompanied by headaches, anxiety and irritability.
According to the Mayo Clinic an intake of more than 600mg of caffeine per day - four to seven cups of coffee - risks causing restlessness, abnormal heart rhythms and stomach upset.
Caffeine effects people in different ways. Individuals under stress and those who are not regular coffee drinkers have a higher sensitivity. Other factors contribute to variations in caffeine tolerance as well, including age, smoking habits, drug or hormone use, and other health conditions, such as anxiety disorders.
"Coffee is a stimulant and like most stimulates, drinking too much will make you feel unwell," says nutritionist Sarah Keogh.
Because of caffeine's moderately addictive nature, cutting back severely sometimes results in withdrawal symptoms, which feel similar to a mild hangover.
Coffee has also been linked to insomnia - though there are cases of it helping people sleep more soundly.
A 2003 Danish survey found that heavy consumption of coffee during pregnancy significantly increased the risk of stillbirths (although there was no rise in the likelihood of infant death in the first year).
The "safety threshold" for pregnant women, according to the study, was four to seven cups a day. Those who drank eight or more cups a day were at 220 per cent increased risk compared to non-drinkers. It has been suggested too that coffee may heighten the chances of osteoporosis in post menopausal women although the evidence is not universally regarded as conclusive, says Keogh.
"The argument goes back and forth but it has been shown that women who drank more than three or four cups a day had a lower bone density. Whether this was specifically caused by the coffee is a matter for debate," she says.
The beneficial effects of coffee are less contentious. Caffeine boosts the effectiveness of painkillers - especially migraine medications - and can rid people of asthma.
Some of the benefits are gender specific; for instance caffeine has been shown to reduce suicide for women, and prevent gallstones and gallbladder disease in men. It also decreases the incidence of diabetes in both sexes but lowers the risk by about 30 per cent in women and over 50 per cent in men.
"Like many things in life, coffee can be both good and bad for you," says nutritionist Elaine Boyle. "Ultimately it depends on the individual. If you are constantly feeling strung out and nervy then perhaps you should consider cutting back."