B Vitamins & Cognition: What's the Link?

You've heard me say over & over again - look for trends, not fads, when it comes to medical literature.  A corollary is never be the first, but never be the last either, when it comes to new medications (and procedures).  However, while you wait for more evidence to accumulate, it's always a good idea to closely evaluate the existing literature to determine if the evidence really supports the conclusions.

For instance, several studies over the last coupe of years have been published demonstrating no effect of B vitamins (B6, B12 & folate) on cognitive decline.  For instance, in October 2008 in JAMA, the authors concluded that high dose B vitamins did not slow cognitive loss in 340 patients w/mild to moderate Alzheimer's disease over 18mo.  Then in December 2008 in American Journal of Clinical Nutrition, the authors concluded that B vitamins did not slow cognitive loss in women w/heart disease (risk factors) over 5yrs.

In June 2010 in American Journal of Medicine, authors concluded that B vitamins for 6mo had no effect on cognitive function over 3yrs in a meta-analysis of 9 randomized, placebo controlled trials involving 2,835 participants.  Finally, in October 2010 in Neurology, authors concluded that B vitamins did not improve cognitive function over 2yrs in hypertensive men older than 75yo.

If you've read this far, you'd conclude fairly that B vitamins do not slow down cognitive loss, much less improve cognitive function in largely disparate populations, eg patients with mild to moderate AD, women w/heart disease (risk factors), close to 3,000 in the general population, and hypertensive men older than 75yo.

But as I've also quoted, the devil is in the details.  In the October 2008 study, the patients all had normal folic acid, vitamin B12, and homocysteine levels.  Why would you expect any improvement if you're already normal?  In a subset of the December 2008 study, those women who had a low baseline intake of B vitamins actually demonstrated preservation of cognitive function when given B vitamins.  In the June 2010 study, the participants received a median of 3mo of supplements which probably was not enough time to make a difference.  And finally, in the October 2010 randomized placebo controlled study, homocysteine levels were essentially normal (at the upper end of the reference range) to start.  Again, why would you expect any improvement if you're already normal at baseline?

Therefore, perhaps it's not such a surprise then that a randomized placebo-controlled study published in this month's AJCN concluded that B vitamins over 2yrs can improve cognitive function in depressed elderly, a small but significant niche group.  Why am I not surprised?  Because we're looking at a very specific group in isolation as opposed to a large group of participants in whom their individual traits cancel out each other.  So in addition to looking for trends, make sure the group assessed has similar demographics to your patients.  Just one more thing to ponder . . .

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