The combination that looked bad was folic acid with a low B12
About a third of American seniors had folic acid circulating unconverted. Among those whose B12 was low, its presence went with lower cognitive test scores.
What the study found
Unconverted folic acid tracked worse cognition where B12 was low
Roughly a third of American seniors had folic acid circulating in a form the body had not converted. Among those whose vitamin B12 was low, its presence went with lower cognitive test scores and a lower mean cell volume, the blood measure that would otherwise have flagged the deficiency.
The caveat · A single snapshot, order unknown
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.
What we don't know
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.