Tuesday, May 26, 2009

Three cups of tea a day 'can cut heart attack risk by 70%'

And pigs might fly. This is just tea industry puffery and one would have to look individually at the raft of findings referred to. As far as I am aware, however, all the human studies are epidemiological and hence incapable of enabling causative inferences. See e.g. here. And one of the studies apparently referred to below was downright dishonest

Drinking three cups of tea a day can ward off heart attacks, a dietician has claimed. The beverage could even have anti-cancer properties, a review of previous research suggests. The link between coronary heart disease and tea has been the subject of a large number of studies.

Dr Carrie Ruxton, a member of the Tea Advisory Panel, analysed some of these, which highlighted the effectiveness of naturally occurring compounds called flavonoids in combating heart attacks. One Finnish study found men who drank more than two cups of tea a day had a 21 per cent reduced chance of stroke. French research showed that women who drank more than three cups a day had a 32 per cent lower risk of blocked arteries.

Dr Ruxton said the research showed at least three cups of tea a day can lower the risk of a heart attack by up to 70 per cent. She said: 'We are not sure of the exact mechanism, but it is thought that tea flavonoids could be involved in controlling inflammation, reducing thrombosis, promoting blood vessel function and helping to limit furring up of the arteries.' The studies found tea may be 'a useful addition to an anti-cancer diet', she added, but further research was needed.

Dr Ruxton said: 'Tea may be a national favourite but it also has health benefits thanks to its high flavonoid content. 'My research shows there is a growing amount of evidence which indicates tea can play a role in helping to combat cardiovascular problems such as heart disease and stroke. 'This area of research is very exciting for the future. We also found solid evidence of tea helping to boost cognitive function and reduce stress, probably related to tea's modest caffeine content. 'Some interesting research on the role of tea flavonoids in helping to combat certain neurological conditions is emerging.' She added: 'Research shows you do not need to drink gallons of tea to get real improvements just three or four cups of tea a day are enough.'

Dr Catherine Hood, another Tea Advisory Panel member, said: 'The scientific community is learning more and more about tea and its health properties. 'Studies show that there are some very powerful ingredients in tea that can play a hugely important role in protecting the body from some serious and potentially fatal conditions. 'A cuppa is a great way to relax or unwind but could also give your health a crucial boost. 'Just a few cups a day have been shown to help and drinking more isn't a problem either as up to eight cups a day have been shown to be fine.'

Tea is the most consumed drink after water with 131,150 tons of tea consumed in the UK in 2006/07. Nearly eight in ten adults drink an average of 2.3 mugs a day.


How to lie with statistics — sometimes without even trying

Some old and simple truths below but they are much forgotten truths too

Some time back, there were news stories reporting on studies of several communities that showed smoking bans to be followed by reductions in heart attacks. There are now reports of a much larger study done at the NBER which finds no such effect. How can one explain the discrepancy?

The simple answer is that in some communities heart attack deaths went up after smoking bans, in some they went down, in some they remained more or less unchanged. Hence a study of a single community could find a substantial reduction even if it was not true on average over all communities.

How did the particular communities reported in the early stories get selected? There are two obvious possibilities.

The first is that the studies were done by people trying to produce evidence of the dangers of second hand smoke. To do so, they studied one community after another until they found one where the evidence fit their theory, then reported only on that one. If that is what happened the people responsible were deliberately dishonest; no research results they publish in the future should be taken seriously.

There is, however, an alternative explanation that gives exactly the same result with no villainy required. Every year lots of studies of different things get done. Only some of them make it to publication, and only a tiny minority of those make it into the newspapers. A study finding no effect from smoking bans is much less likely to be publishable than one that finds an effect. A study finding the opposite of the expected result is more likely to be dismissed as an anomaly due to statistical variation or experimental error than one confirming the expected result. And, among published studies, one that provides evidence for something that lots of people want to believe is more likely to make it into the newspapers than one that doesn't.


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