Vitamin D vs Frailty: Too Much of a Good Thing?

Don't kill the messenger.  I'm a big fan of vitamin D.  After reading quite a bit of research over the last year or so, I believe that we generally don't have enough vitamin D which can severely impact our health.  So we mostly agree that not enough vitamin D is bad.  The disagreement comes when we try to figure how much is enough.  Just last week, I chastised the IOM (yeah, as if they had any idea who I am or even cared) because I thought they were overly conservative in their vitamin D recommendations.

Well, in a study published this month, the authors performed a cross sectional & longitudinal 4 year study of 6,307 women >69yo.  Not surprisingly, those with the lowest vitamin D (<15ng/mL) were at the greatest risk of becoming frail (which in itself opens up another can of worms regarding how one defines frailty).  Those with vitamin D ranging from 15-19.9ng/mL were intermediate in risk of becoming frail compared to those with levels 20-29.9ng/mL.  But surprisingly, those with levels >30ng/mL also had a greater risk of becoming frail such that the authors described a U shaped curve in terms of frailty vs vitamin D level.

How to explain this if you're in vitamin D's corner?  Perhaps, they studied participants too late for vitamin D to make a difference.  But regardless of baseline functional status, the lower one's vitamin D, the greater one's risk for becoming frail.  Perhaps, those who were already frail were taking lots of supplements to remedy their condition.  No one knows right now.

Please understand that correlation does not imply causation.  However, while many other studies have demonstrated negative outcomes associated with low vitamin D, there have been no randomized double blind placebo controlled studies (this is the gold standard for proof) demonstrating a higher ceiling effect. 

As with many things in life, perhaps too much of a good thing isn't good for you?  Perhaps, we should strive for just right, rather than too much?  Let's learn from Goldilocks!