Our CTV television network, which prides itself in presenting the
very latest in medical advances, adequate evidence or not, had
another one tonight. A randomized controlled study which
showed that a 2-year regimen of B vitamins in the elderly with
mild cognitive impairment slows the rate of MRI-assessed brain
atrophy.
But funny, I said to my wife, there's no mention of cognitive
improvement. Surely in a clinical study of this size and
sophistication, not to mention expense, they would measure
cognition before and after treatment. And if they did, wouldn't
they be bound to mention the outcome? Think again.
The study turns out to be Smith et al (2010). They took a battery
of cognitive measures, all right, but there was nothing in the
methods I could see noting that they took these measures after
treatment as well as before. But apparently they did.
Buried in a section labeled "secondary outcomes" was this
statement "Although the study was not powered to detect an
effect of treatment on cognition (findings to be reported
separately), in a post hoc analysis we noted that final cognitive
test scores were correlated to rate of atrophy".
My translation: We didn't find any difference between placebo
and vitamin treatments in cognition, so we did what we could to
put a positive spin on this, and also to forget about it. Anyway, if
we had more subjects, we might have seen something (the "not
powered" excuse).
They provide a brief similar excuse ("not powered to detect
effects of treatment on cognitive test scores") in a later section
titled "Possible therapeutic implications". No data, of course.
But curiously, if one goes to where they registered their trial
before it began, they specified that in their study a "primary
outcome measure" was "Changes in performance on a variety
of cognitive tests". Nothing there about "not powered".
See:
http://www.controlled-trials.com/ISRCTN94410159/94410159
So it seems that in their haste to get out the good news
(vitamins slow brain atrophy, which is indeed impressive), they
somehow avoided providing the bad news (no detectable effect
on cognition). Perhaps providing it would tend to dampen sales
for the products for which Dr. Smith is listed as inventor with
patents held by the University of Oxford and on which he "could
benefit financially" (see "competing interests").
Stephen
Smith, A. et al (2010). Homocysteine-lowering by B vitamins
slows the rate of accelerated brain atrophy in mild cognitive
impairment: a randomized controlled tria. PLoS ONE,
September 2010, v. 5, issue 9, e1244
Available here:
http://tinyurl.com/Bvitamins-for-the-brain
--------------------------------------------
Stephen L. Black, Ph.D.
Professor of Psychology, Emeritus
Bishop's University
e-mail: sblack at ubishops.ca
2600 College St.
Sherbrooke QC J1M 1Z7
Canada
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