Ben goldacre, The Guardian, Saturday 6 March 2010
If the media were actuarial about drawing our attention to the causes of avoidable death, your newspapers would be filled with diarrhoea, Aids, and cigarettes every day. In reality we know this is an absurd idea. For those interested in the scale of our fascination with rarity, one piece of research looked at a 3 month period in 2002 and found that 8,571 people had to die from smoking to generate one story on the subject from the BBC, while there were 3 stories for every death from vCJD.
So you’ve probably heard that smoking might prevent Alzheimers. It comes up in the papers, sometimes to say it’s a true finding, sometimes to say it’s been refuted. Maybe you think it’s a mixed bag, that the research is contradictory, that “experts are divided”. Perhaps you smoke, and joke about how it’ll stop you losing your marbles, at least.
This month, Janine Cataldo and colleagues publish a systematic review on the subject, but with a very interesting twist. First they found all the papers ever published on smoking and alzheimers, using an explicit search strategy which they describe properly in the paper – because they’re scientists, not homeopaths – to make sure that they found all of the evidence, rather than just the studies they already knew about, or the ones which flattered their preconceptions.
They found 43 in total, and overall, smoking significantly increases your risk of Alzheimers. But they went further. 11 of the studies were written by people with affiliations to the tobacco industry. This wasn’t always declared, so to double check, the researchers searched on the University of California’s Legacy Tobacco Documents Library, a vast collection of scanned material which has been gathered over decades of legal action.
If you ever want to spend a chilling afternoon living in the head of an industry whose product has been proven to kill a third of their customers, this is the place for you. “The importance of younger adults” uses financial modelling to explain the importance of recruiting teenage smokers to replace the dying older ones before it’s too late, and explains that “repeated government studies have shown less than one third of smokers start after age 18 [and] only 5% of smokers start after age 24.” “Youth cigarette – new concepts” from Marketing Innovations Inc takes these ideas further, into cola and apple flavour cigarettes, because “apples connote goodness and freshness”.
How much did it matter if the researchers had worked for the tobacco companies? A lot: the risks of Alzheimers associated with smoking reported by these papers were on average about a third lower than those conducted by other researchers, and they produced many papers showing cigarettes were actively protective. If you exclude these 11 papers, and look only at the 32 remaining, your chances of getting alzheimers are vastly higher: for the gamblers out there, comparing a smoker against a non-smoker, the odds of getting Alzheimers are higher by 1.72 to 1.
So does that mean we can comfortably ignore all research that comes from people who disgust us? In the 1930s, identifying toxic threats in the environment became an important feature of the Nazi project to build a master race through ‘racial hygiene’. Two researchers, Schairer and Schöniger, were working on biological theories of degenerate behaviour under Professor Karl Astel, a scientist who helped organise the vile “euthanasia” operation that murdered 200,000 mentally and physically disabled people.
In 1943 his two researchers published a well conducted case-control study demonstrating a relationship between smoking and lung cancer almost a decade before any researchers elsewhere. Their paper wasn’t mentioned in the classic Doll and Bradford Hill paper of 1950, and if you check in the Science Citation Index, it was referred to only four times in the 1960s, once in the 1970s, and then not again until 1988, despite providing a valuable early warning on a killer that would cause 100 million early deaths in the 20th century. It’s not obvious what you do with evidence from untrustworthy sources, but it’s always worth appraising its untrustworthiness with the best tools available.