HAVE your friends and neighbours become unusually jittery? A mass caffeine overdose could be to blame. Scientists have discovered coffee isn’t as bad for your heart as once thought – and anyone reading this week’s headlines could be forgiven for thinking they had received carte blanche to sink espressos with abandon.

“Perk up, that 25th cup of coffee won’t harm your heart,” exclaimed The Times. “Up to 25 cups of coffee a day safe for heart health,” said The Guardian, which also challenged a journalist to test out the theory by drinking 25 cups in a morning. The experiment left the writer feeling “nauseous”, “shaky” and “grim” – and Dr David Katz, founding director of the Yale-Griffin Prevention Research Centre, condemned what he called “silly and irresponsible reporting”.

The new caffeine study – by Queen Mary University of London (QMUL) – had, after all, only claimed that drinking large quantities of coffee does not, as previously believed, put pressure on the heart by stiffening the arteries. And as Katz pointed out, that doesn’t make it safe, with insomnia, high blood pressure and heart rate all possible effects of “extreme coffee consumption”.

The British Heart Foundation (BHF) – which co-funded the QMUL research – also seemed annoyed by what it called “misleading” reports and released a statement pointing out its study had never suggested “unlimited coffee has no effect on cardiovascular health”.

Having read QMUL’s initial press release, however, it doesn't come as a surprise that the reports were so dramatic, because it stated “drinking coffee, including in people who drink up to 25 cups a day, is not associated with having stiffer arteries”. The explanation for this statistic, which came further down the release, was more nuanced.

The 8,412-person study had been divided into three groups: “Those who drink less than one cup a day, those who drink between one and three cups a day and those who drink more than three,” explained the release. “People who consumed more than 25 cups of coffee a day were excluded, but no increased stiffening of arteries was associated with those who drank up to this high limit when compared with those who drank less than one cup a day.” Even the higher-drinking group averaged only five cups a day.

The aim of the research, BHF medical director Professor Metin Avkiran said later, was to better understand coffee’s impact on the heart and circulatory system. “There are several conflicting studies,” he added, “and it can be difficult to filter what we should believe and what we shouldn’t.”

He’s right about that. The advice on caffeine is that around 400mg (four or five cups a day) is a recommended safe level. Last week’s dramatic headlines may have gladdened the hearts of the nation’s baristas, but they also provoked grumbles over yet another apparent reversal of received scientific wisdom.

“We’ve ‘bean’ had!” chortled the Daily Mail, above a column asking why, oh why, do the “health nannies” get it so wrong? In previous eras, complained columnist Rose Price, butter and eggs have been subjected to “witch-hunts” by the “heart health police” only for advice to be “spectacularly overturned”.

She has a point. Dozens of foods, from eggs, butter and full-fat milk to wine, chocolate and turmeric, have been condemned, rehabilitated and damned again – sometimes repeatedly. Nor is Price alone in being irritated by all these apparent U-turns. Professor Michael Lean, chair of human nutrition at Glasgow University, describes yo-yoing food messages as “a constant bugbear” and “a major obstacle to improving health”.

So why does it happen? Partly, he suggests, it’s because our “obsession” with health and diet means we’re ever ready to blame ailments on our food – and while the boring truth is “there’s no drama attached to nutrition and the improvements that can be made are quite small”, we are hungry for evidence that consuming more of one product or less of another will have radical effects.

And there is no shortage of research scientists happy to oblige. “There are people in certain universities, especially in America, who crave publicity because that’s how they get their research funds,” says Lean, adding that the press is also “very keen to amplify anything that seems contentious”.

More humdrum research confirming what scientists already know is less likely to get reported. As a result, we only see reports that seem to conflict with what we were previously told.

Caffeine seems particularly prone to this, partly, says Lean, because it’s “the most valuable cash crop in America after oil ... And the minute you put something in about coffee, somebody will say the opposite”.

Studies that log eating habits against incidence of disease are notoriously unreliable, he says, quoting an old adage that “just because 90% of people die within an hour of drinking a cup of tea doesn’t mean the tea has killed you”.

Likewise, people who drink more coffee may seem to suffer more from certain complaints. “But people who drink more coffee tend to smoke more – or at least, they did in the past. So that’s a clear confounding factor. There are all sorts of reasons why survey data has to be interpreted with great caution.”

Even scientific journals aren’t always balanced – particularly on the emotive subject of sugar, says Lean. Research by his department showed a study linking sugar with disease is “more likely to get publication in a good journal than one which shows there’s no effect”. “There’s bias that runs right through the [scientific] journals,” he adds.

What, then, can a confused member of the public believe? Lean reminds us that official healthy eating guidelines have generally been produced by generations of scientists assessing “the totality” of research evidence.

Dramatic studies suggesting shortbread will shorten your life or lettuce will let you live forever should be taken with a pinch of salt – a small one though, as scientists can’t agree over how much sodium is too much.

Shaky grounds

In the 1500s, coffee was blamed for causing sexual promiscuity but it was later hailed as a health food said to aid digestion, relieve coughs and prevent everything from gout to miscarriage. In 1674, the Women’s Petition Against Coffee claimed it caused impotence but by the 1700s it was being promoted as a stimulant that helped people work longer. In subsequent centuries the drink was variously accused of causing blindness, stunting growth and hampering academic study.

In the 1970s, high coffee intake (six or more cups a day) was linked to heart attacks and high blood pressure but more recently it’s been claimed caffeine consumption can reduce the risk of everything from melanoma to Alzheimer’s disease. Last year, a review of scientific literature published in the British Medical Journal concluded that drinking three or four cups of black coffee a day provided health benefits but it also linked large quantities consumed during pregnancy to low birth-weight babies and stillbirths.

The latest research, by QMUL, suggests coffee does not, as previously believed, put pressure on the heart by stiffening the arteries. But if you want to toast that news, don't do it with 25 espressos.

Judged spreads

Although butter was long considered healthy, in the late 20th century concern about saturated fats' impact on cholesterol levels led to a switch to margarines marketed as “high in polyunsaturates”.

Butter has since enjoyed a renaissance and as Glasgow University’s Michael Lean explains, the saturated fats in dairy produce differ from those found in meats and don’t have the same effect on cholesterol. Healthy eating guidelines “glossed over” that distinction, and while Lean understands the need to simplify complex nutritional physiology, he says scientists “got it wrong basically by lumping all saturated fats together”.

Margarine itself fell from grace a few years ago over the potential harmful effects of trans-fatty acids and while commercial spreads have since been modified, sales have plummeted. Meanwhile, the butter vs margarine debate continues.

Yolk and mirrors

During the 1950s and 1960s, The Egg Marketing Board’s “go to work on an egg” slogan promoted this compact, natural foodstuff as a healthy breakfast for hard-working people.

Eggs were later vilified for their supposedly high cholesterol content and people were advised to eat no more than two or three a week. Then in 1988, junior health minister Edwina Currie said that “most of the egg production in this country is affected with salmonella” – and sales nose-dived. Consumer confidence has since been restored and the NHS website now says there is no recommended weekly consumption limit, describing eggs as good sources of protein, vitamins and minerals.

The story of E

During the late 20th century, health-conscious consumers were obsessed with “E numbers”, which referred to the classification of the 319 preservatives, flavour enhancers and other food additives approved for use in the EU. The system was meant to regulate additives and remove toxins from foods and many of the substances listed on products were harmless (E300 is vitamin C and E160 is paprika).

Consumers were suspicious, however, and the flavour enhancer monosodium glutamate or MSG (E621) was one of the biggest bogies, blamed for causing headaches, nausea and numbness: symptoms collectively dubbed “Chinese restaurant syndrome” because the seasoning was commonly used in those establishments.

Washington University researchers conducted experiments that produced stunted growth and sterility in mice and monkeys – but subsequent studies, including on humans, failed to repeat the results and today the Food and Drug Administration says the substance is “generally recognised as safe”.