All women who are considering having a baby are encouraged to take folic acid. Some countries include the vitamin with their flour - to ensure all women get it.
The reason is that it has a dramatic impact in preventing the disability spina bifida and a range of conditions called neural tube defects.
So today's report linking it to the development of asthma in children is potentially alarming - as it might deter women from taking this important vitamin.
The Australian researchers stress their findings only apply to the taking of the vitamin in late pregnancy. To prevent spina bifida, it needs to be taken before conception or in early pregnancy.
However it does raise questions about adding folic acid to flour - as it might lead to women being over-exposed in late pregnancy.
The Englemed report allows you to link through to the original article.
We've seen some criticism of the research which says the following:
it was conducted by postal survey;
only 76 per cent of women took part.
If that was so, it would make it dangerously flawed as the increase in asthma risk is only about 23 per cent.
However those criticisms only apply to the final stage of the research, when the children were aged five. And no link with asthma was established at this age.
Most of the research was, in fact, done by research nurses who conducted interviews with the women. When the children were aged three, the women were interviewed again and this is the age at which the link with asthma was found. At this point 88 per cent of the original sample were taking part, just four percentage points fewer than the 92 per cent who successfully gave birth.
The numbers involved - just over 500 families - are not enormous so the findings have to be treated with caution. It does not seem they can be dismissed out of hand.
Asthma is quite a common condition in young children and a small increase could affect quite a few children. Ironically, folic acid fortification of flour was introduced in Australia after this research was done.
It will be interesting to see what other analysts make of this and what further research is done. For, yet again, it is thought-provoking research that raises some tricky issues.