Date	Event	Description
27 June 2012	New search has been performed	Three further studies are included (Ma 2006, Wang 2000, Xuan 2007) and 24 studies have been added to the "excluded studies table". The text has been rewritten and every included trial assessed with the 'Risk of bias' tool. The main findings did not change substantially.
27 June 2012	New citation required but conclusions have not changed	Substantive update: conclusions not changed