NIH distorts report showing risk of stroke after chiropractic

Why would an NIH center try to mislead the public about a newly published study that it funded? Last month NIH’s alternative medicine center, NCCIH, highlighted one of its studies with this headline: “Low risk of stroke after chiropractic spinal manipulation in older patients with neck pain, study finds.” 

This sounds reassuring, unless you read the study. It turns out that the risk of stroke was 10% higher in patients who saw a chiropractor compared to those who saw a regular doctor. Yet NIH wants us to believe that the study found no serious risk.

Why ask this question? Because earlier studies showed a small but frightening risk of stroke in younger people (45 and below) after chiropractic, caused by dissection of the vertebral artery. Strokes caused by a tear in this artery are extremely rare, but even a tiny possibility of a fatal stroke after a chiropractic manipulation is alarming. As Forbes writer Larry Husten reported last August, the American Heart Association and the American Stroke Association issued a statement warning that chiropractic neck adjustments might cause strokes. The AHA stated:
  • "Manipulating the neck has been associated with cervical dissection, a type of arterial tear that can lead to stroke.
  • Although a direct cause-and-effect link has not been established between neck manipulation and the risk of stroke, healthcare providers should inform patients of the association before they undergo neck manipulation."
I’ve written about this as well, both at Forbes and in The Atlantic Monthly. The risk is small but the consequences can be extremely serious.

So what's in this new study? The study, led by chiropractor James Whedon at Dartmouth College, was a large-scale survey of Medicare claims involving people aged 66 to 99. Its aim was to answer this question: "what is the probability of stroke following chiropractic spinal manipulation, as compared to a control group of subjects evaluated for neck pain by a primary care physician?" Key findings from the study included these (all from Table 2):

                     Hazard ratio for stroke at 30 days
All patients         1.10 (10% increase)
Patients aged 75-79  1.93 (93% increase)
Patients aged 80-84  2.50 (2.5 times more likely)
Patients over 85     3.59 (over 3.5 times more likely)

This looks bad: for all patients, the risk of stroke was 10% higher if they'd seen a chiropractor versus a regular doctor. In the older patients, the risk of stroke after 30 days was 1.9 to 3.6 times higher than for patients aged 66-69. (All four of these results were reported as statistically significant.) Yet the conclusions of the study–and the NIH press release–make no mention of these findings. The study itself concludes only that 
Among Medicare B beneficiaries aged 66 to 99 years with neck pain, incidence of vertebrobasilar stroke was extremely low. Small differences in risk between patients who saw a chiropractor and those who saw a primary care physician are probably not clinically significant.”
Talk about spin! The study provides no support for the dismissive statement that the increase in risk of stroke after chiropractic is "not clinically significant"; it seems they are trying to downplay their own finding of a statistically significant increase in risk. The NIH’s press release is just as bad: it merely parrots the study's conclusions, opening with the statement that “cervical spine manipulation is unlikely to cause a stroke,” and never mentioning the statistically significant 10% increase in risk or that the study was led by a chiropractor.

Despite the misleading press release, this new study adds to the evidence that chiropractic carries an increased risk of stroke, especially for older patients. As the American Heart Association recommends, patients should be informed of this risk before submitting themselves to a possibly dangerous neck manipulation. And NIH press officers should read the study before issuing a press release.


  1. Your overall point may still be valid (I'm not commenting on that), but I believe you are misinterpreting the estimates of the age coefficients in Table 2 of the paper. Those are the hazard ratio estimates for those age categories compared to the age category 66-69. So, for example, it is saying that the hazard of stroke for people aged 75-59 is 1.93 times that of people aged 66-69, controlling for whether they received chiropractic care, sex, race, and comorbidity score. It is not comparing the effect of chiropractic care on stroke risk between different age groups. I agree that would be interesting to estimate, and they clearly do have the sample size to be able to be able to do it, but it does not seem like they did it (or at least they did not report it).

    1. sorry, I meant *aged 75-79* of course.

  2. Anon: you are correct, the table was very badly formatted and I mis-interpreted it initially, because the entire study was about chiropractic vs regular care and stroke risk. I revised the blog post to reflect this; the increase in risk is only 10%. But there's still an increase, and it's statistically significant (as they report).

    1. Thanks! Also, I appreciate you taking the time to do this kind of reporting!

    2. I can see where the confusion would come from because they say "The risk of stroke in general increases with age, but it is not known how age might affect the risk of stroke after spinal manipulation", the point of which seems to me to be that looking at how the effect of spinal manipulation on stroke risk varies with age is important. But then they never end up doing that for some reason.

      But anyway, given that they don't, I would opine that since it is already well established that stroke risk increases with age, it is not surprising that those results (the estimates for the age coefficients) were not highlighted in the conclusions or in the press release.


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