Effects of vitamin D supplementation on bone density in healthy children: systematic review and meta-analysis

BMJ 2011; 342 doi: http://dx.doi.org/10.1136/bmj.c7254 (Published 25 January 2011)
Cite this as: BMJ 2011;342:c7254

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We do not ignore the results of statistical analysis - in fact we very clearly state in the article whether or not results were statistically significant at the 5% level. We agree with the view, also held by others, that the interpretation of results of data analysis does not solely rely on the classification of results into statistically significant or not according to the arbitrarily chosen but widely accepted p-value of 0.05 (1). We used the word trend where p-values were between 0.05 and 0.10. We highlighted results which, while not statistically significant, suggest that clinically important results should not be ruled out and in turn discussed when these may suggest directions for the further studies required to provide the definitive results necessary to guide practice and potentially improve health outcomes. In the context of our study, where power is limited by the number and size of studies available, we are of the opinion this is a particularly important contribution to the interpretation of the study's findings.

1. Rothman KJ, Greenland S. Modern epidemiology. Philadelphia: Lipncott-Raven; 1998.

Competing interests: None declared

Tania Winzenberg, Senior Research Fellow

Graeme Jones

Menzies Research Institute Tasmania, University of Tasmania

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28 January 2011

Winzenberg et al repeatedly use the phrase "There was a trend..." to describe a result which they have shown to be statistically nonsignificant. "There was no trend..." would be more accurate. This is not pedantry: why bother with statistical analysis if the results are to be ignored?


Competing interests: None declared

Jeffrey R. Johnstone, retired


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Editor, I read the recent publication by Winzenberg et al. with a great interest. I agree with the conclusion that "It is unlikely that vitamin D supplements are beneficial in children and adolescents with normal vitamin D levels [1]." Indeed, this is a simple thing that both "too many" and "too few" are not appropriate for healthy life. Indeed, there is no report concerning the adverse effeect due to over intake of vitamin D in pediatric population. Finally, I would like to raise a question how the appropriate level can be judged for each individual. Have we to wait until there are overt symptoms?


1. Tania Winzenberg, Sandi Powell, Kelly Anne Shaw, and Graeme Jones. Effects of vitamin D supplementation on bone density in healthy children: systematic review and meta-analysis. BMJ 2011 342:c7254; doi:10.1136/bmj.c7254

Competing interests: None declared

professor viroj wiwanitkit, director, physician

wiwanitkit house, bangkhae, bangkok thailand

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