Folic Acid

Five years cannot rule out a cancer that takes longer to appear, and the authors confine their conclusion to that window. The interval reaches a rate ratio of 1.13, so a modest increase is not excluded, only a large one. Almost everyone enrolled was a middle-aged or older adult in a heart-disease or bowel-polyp trial, so the reassurance reaches women of reproductive age by argument rather than by measurement.

The 4mg dose tested here is ten times what the general population is now told to take. The trial was stopped early once the result crossed its stopping rule, which tends to make an effect look larger than it is. Twenty-seven defects occurred in the whole trial, so the estimate is rough. Every woman enrolled had already had an affected pregnancy, so this says nothing about a first one.

A plateau is not a threshold. This models how long a level takes to stop rising, not how long until enough folate is present to protect an embryo, and those are different points. The 906 nmol/L target it is anchored to comes from observational Chinese data rather than a trial. Most of the pooled studies were in adults who were not pregnant, and red cell folate assays are notoriously hard to compare between laboratories.

None of this means 400 micrograms is the wrong number. It means nobody ran that trial. The Task Force reaffirmed its position rather than reviewing the evidence from scratch, and it gives a range without saying where in the range to sit. Its advice also addresses a country whose flour has been fortified since 1998, so the benefit of a tablet on top of that is not the benefit the old trials measured.

The clinical cases that established this used folic acid above 5mg a day in the 1940s and 1950s, roughly ten times a modern supplement and far above what fortified flour delivers, so it does not transfer straight to a 400 microgram tablet. The authors of the review say themselves that the modern evidence is correlative or from uncontrolled observation, and that their proposed mechanism has not been tested. They are also the group that proposed it.

The high-dose figure is deliberately absent here. The Canadian guideline states its tiers qualitatively rather than in milligrams, so no number can honestly be quoted from it, and an old trial dose is not a current recommendation. Both documents are graded syntheses of other people's work, resting partly on expert opinion where trials do not exist, and both address populations whose flour has been fortified since the 1990s.

None of this was randomised. These are before-and-after comparisons, so anything else that changed over the same years counts too: prenatal screening improved, supplement campaigns ran alongside the fortified flour, and registries differed in what they counted. What this design cannot do is separate the flour from the campaign that arrived with it.

The 121 million figure is a model, not a count, built from country surveys of uneven quality and published with an 80% uncertainty range of 112.8 to 131.5 million. It also says nothing about who was or was not taking folic acid. The week-four timing comes from a clinical reference chapter that gives no study for it.

An absence of proof is not proof of absence. Only five randomised trials of folate around conception exist at all, and just one was judged at low risk of bias. What this shows is that a question most people assume was settled by trial was put to a single small trial that could not settle it.

Whether folic acid prevents a first neural tube defect has never been put to a trial large enough to settle it. The one trial rests on six defects, all in one arm, and reviewers disagree on what that can carry.

Homocysteine is a blood marker, not a birth outcome: this trial says nothing about whether either form prevents a neural tube defect. The 144 women were split across four arms, so each is small, and none was selected by genotype, which is the comparison the marketing claim actually turns on. A co-author affiliation with the maker of the methylated preparation is worth checking before the result is quoted in either direction.

Whether methylfolate beats plain folic acid in carriers of the MTHFR variant, a folate-activating enzyme gene, is not shown. The trial cited for it had no folic acid arm; the one that compared the two forms found no advantage.

This measures exposure, not harm. The authors say plainly that it does not show anyone was hurt, and call for the functional consequences to be investigated. It is one Toronto cohort of 368 women in a country with mandatory fortification, so these intakes are not typical of unfortified populations, and assay differences make the comparison with older, lower published values unreliable.

This is a single snapshot in time, so it cannot say which came first. The finding sits inside a subgroup defined by poor B12 status, well under the 1858 people surveyed, which is where chance findings live, and the authors describe some of their own results as unexpected and internally inconsistent. In the people whose B12 was normal, more of the natural circulating folate went with better scores, not worse.