Sunday, October 13, 2013

Statins Cut Stroke Risk by 40%?

The source of the article, written by a certain Jenny Hope, was a study published online this month in the journal Stroke.  The print version will be coming out in December. The title of the study is Age and Ethnic Disparities in Incidence of Stroke Over Time, and the authors are Yanzhong Wang, PhD; Anthony G. Rudd, FRCP; Charles D.A. Wolfe, MD, FFPH.

The Mail Online's screaming headline would have you believe statins were responsible for a massive 40% decrease in stroke risk.  What's not to like about that?

Quite a bit, as it happens.  The big problem I have with the headline is that the cause of the reported decrease doesn't appear anywhere in the actual study!  The only reference is this little sentence:

Improvements in prevention could come from any number of interventions, which may or may not include statin drug prescriptions.

But there are other aspects that are disturbing.  A 40% improvement in stroke incidence is great, but doesn't apply to blacks, or people aged 15 to 44.  

More people are now getting strokes at a younger age.  The mean age dropped from 71.7 to 69.6, which I expect is due to the higher proportion of younger stroke patients:

The fact that the glowing results were not across the board, is a strong suggestion that statin usage was not the simple causal factor for the decline in stroke incidence that the Mail would like you to believe.  Of course, it is possible that on average, younger people and blacks did not receive the same proportion of preventative health care interventions, including statin prescriptions, that white elderly people were provided with.  

I am curious to know whether black people were, on average, given similar interventions.  Were the drugs they were prescribed less efficacious, were they even offered statins, or were other factors at play?  This is very important to know if you are black and your doctor wants to prescribe a statin to you.

Statins are not the only drugs used to reduce the risk of stroke.  Hypertension is a major factor too, and blood pressure medication also plays a large part.  Why were statins and not blood pressure medication singled out in the headline as the cause underlying the changing trends?

The study authors point out that they are not sure why stroke risk rose among younger people, particularly blacks, though they did recognize that there is a general rise in cardiovascular risk factors:

Lastly, the types of stroke changed, which a shift from hemorrhagic to ischemic strokes.  I am curious why this might be.

What does this mean?  In my opinion, it is a good example of why it is important to refer to the actual studies when newspapers quote dramatic cause and effect results.  The journalists writing the articles have an uncanny facility for jumping to conclusions that are not at all mentioned in the studies they quote.  It can take some detective work to distinguish important statistical outliers from the overall results.

The public is often quick to suggest that studies are biased because of who is funding them;  however, in this case, it is not the study that is flawed or biased, but the media hype surrounding the study.

Edit:  After posting this, I found Zoe Harcombe's take on the same study.  She was also baffled by the attribution of cause in the newspaper headline that wasn't noted anywhere in the actual study.  In Zoe's words, the headline "is a lie. It is simply not true. It is disgraceful ‘journalism.’"

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