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Comment & Response
June 2016

Does Metformin Really Increase Height, or Is There Some Problem With the Controls?—Reply

Author Affiliations
  • 1Faculty of Physical Education and Recreation, Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
  • 2Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada
JAMA Pediatr. 2016;170(6):621. doi:10.1001/jamapediatrics.2015.4965

In Reply We thank Poulton for the thoughtful letter that stated that the greater increase in height observed in studies from our meta-analysis1 with the highest cumulative metformin dose was owing to “a combination of inaccurate and abnormally slow growth rates in the control individuals.”

We agree that artifacts could arise from a higher attrition level in the study by Kendall et al,2 and understand why it is tempting for Dr Poulton to suggest that we should reanalyze without this study. However, we disagree that we should exclude an individual study owing to its attrition level without applying this criterion to all studies (eg, the study by Mauras et al3 had the highest control group attrition rate but a −0.2-cm change in height in the metformin vs the control group). While the changes in height in the control group from Kendall et al2 (ie, 1 cm in 6 months; mean baseline age of 13.6 years) may seem “suspiciously slow,” it is not dissimilar from other studies we reviewed that were comparable in terms of duration and participants’ baseline age. This “slower growth than normal in the controls” may therefore be explained by findings that suggest children with obesity have an earlier peak height velocity and onset of puberty, but lower peak height velocity.4 For these reasons, we believe it would be inappropriate for us to single out and exclude the data from Kendall et al.2

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