| Date | Event | Description |
|---|---|---|
| 29 July 2011 | New search has been performed | Updated literature searches 2006 to 2011. |
| 29 July 2011 | New citation required and conclusions have changed | We added eight studies involving 3015 participants, strengthening the lung function result. 'Risk of bias' has been updated to the latest tool. |
| 22 June 2008 | New search has been performed | Converted to new review format. |
| 6 January 2007 | New citation required and conclusions have changed | Substantive amendment. |
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