In both the print and web versions of this Head to Head article by Nicholas J Wald and Godfrey P Oakley (BMJ 2007;334:1252, 16 Jun, doi: 10.1136/bmj.39232.493252.47) the word “deficiency” appears unnecessarily in the discussion of whether folic acid exacerbates B-12 deficiency. The relevant sentence should read: “...high dose folic acid can reverse the arrest of DNA synthesis that causes a B-12 macrocytosis [not B-12 macrocytosis deficiency].”

Also, during editing for the print version, several headings were omitted; readers are advised to consult the full version on bmj.com, which includes headings stating the four concerns that the article rebuts: that folic acid may cause cancer; that randomised trials have shown no benefit in cardiovascular disease; that folic acid may make B-12 deficiency worse; and that folic acid is a form of folate that does not occur in nature.