Paper linking vitamin C and reduced asthma retracted after authors find “severe” problems with data
It’s never a good sign when a paper has “severe” problems with its data. But when even the researchers are at a loss to explain how those problems made their way into the manuscript, well, that’s downright alarming.
Consider: The journal Clinical and Translational Allergy has retracted a 2011 article by researchers from Egypt and Finland, who have been studying the effects of vitamin C on childhood asthma. In a previous article, published in 2009 in Acta Paediatrica, members of the team reported that
Diet supplementation with omega-3 fatty acids, Zn and vitamin C significantly improved asthma control test, pulmonary function tests and pulmonary inflammatory markers in children with moderately persistent bronchial asthma either singly or in combination.
In the follow-up study — a 60-patient, crossover trial — they claimed to have found that
The effect of vitamin C on the FEV1 levels was significantly modified by age and exposure to dampness. In the children aged 7.0-8.2 years with no exposure to dampness, vitamin C increased the FEV1 level [a measure of lung function] by 37% (95% CI: 34-40%), whereas in the children aged 8.3-10 years with exposure to dampness or mold in their bedroom more than one year prior to the study, vitamin C increased the FEV1 level by only 21% (95% CI: 18-25%).
Except that they didn’t. According to the retraction notice:
We reported that the effect of vitamin C on asthma in Egyptian children was modified by age, exposure to dampness and the severity of asthma, Clinical & Translational Allergy 2011, 1:9. After our paper was published, we found out severe problems in the data set. There were 60 children in the study. The ages were by accident duplicated between the upper and lower halves of the database. Thus, the ages for the first 30 children in the data set were identical and in the same order with the ages for the second set of 30 children. Similar duplication was also found for C-ACT and FEV1 measurements after vitamin C supplementation and for exposure to dampness. This duplication thus directly invalidates the second part of the data set, and thus the reported outcome. We have not been able to sort out the reason for this duplication. The files with the original data are not available any more, making it impossible to reconstruct a valid data set for reanalysis. Therefore we have to retract our paper. The authors deeply regret the inconvenience this has caused to the journal and the scientific community.
So far, the Acta Paediatrica paper, which has been cited just once, according to Thomson Scientific’s Web of Knowledge, has not been retracted. But we note that it, too, involved 60 children — or so it states.