Folate in pregnancy where was the health advice to the public?
Charles et al1 did qualify their findings with several notes of caution and the findings were balanced by the commentary2, however, the title of the article and the main media message presented were misleading and unhelpful.
In statistical terms, of all the tests undertaken (twenty four in total were presented) one was statistically significant. At the 5% level this is to be expected by chance alone. The statistically ‘significant’ finding, was in the group given high dose folate but the outcome was not breast cancer mortality (as the title and the media reports would suggest) but all cancer deaths.
The article stated that the analysis was without a prespecified hypothesis, however, the project grant was from the British Heart Foundation suggesting that the cancer findings were incidental to a mainly cardiovascular focus.
The issue for the public (and the media) is whether there is a causal link between all cancer or breast cancer mortality and folate. Using the Bradford-Hill criteria3 to assess this there does appear to be a dose- response relationship in the findings. Also, the authors refer to findings in rats where levels of folate intake below as well as above normal were at risk of mammary tumorigenesis. Otherwise the strength of the evidence for this link remains limited particularly in comparison with that of folate preventing neural tube defects4.
Assessment of the implications of Charles et al’s findings is also difficult because the recommended daily dose of folate for pregnant women (and those planning pregnancy) is 0.4mg and the study used 0.2mg and 5mg doses.
As the findings are so inconclusive, reporting of this article in the media should have been accompanied by a message reiterating that currently the evidence supported the use of folate in preventing neural tube defects is far stronger and better established than these chance findings. This is just the sort of mixed message about diet and health criticised in the new white paper Choosing Health5. Hopefully further research will lead to clear advice to satisfy public concerns.
1. Charles D, Ness AD, Campbell D, Smith GD, Hall MH. Taking folate in pregnancy and risk of maternal breast cancer. BMJ 2004:329:1375-6.
2. Ockley GP, Mandel JS. Commentary: Folic acid fortification remains an urgent health priority. BMJ 2004; 349;1376.
3 .Bradford-Hill A. The Environment and Disease: Association or Causation? Proc. Royal Soc Med. 1966;58:295.
4. MRC Vitamin Study Research Group. Prevention of neural tube defects: results of the Medical Research Council vitamin study. Lancet 1991;338:131-7.
5. Department of Health. Choosing Health - Making healthy choices easier. November 2004 H M Government.
Competing interests: None declared
Competing interests: No competing interests