Friday, November 28, 2014

What, exactly, DOES constitute a vitamin D deficiency?

A few years ago, my doctor's office had me tested for vitamin D.  They were testing everyone, they said -- apparently it had become the thing to do.  My labs showed my vitamin D was over the minimum, but only just barely, so they wanted me to take a supplement.

I ignored that.  I am not a big believer in supplements.

Fast forward to just a few days ago, when I saw a story on NPR about vitamin D... which, ultimately, made me feel very justified for having ignored the ultra-serious recommendation that I needed a supplement.

Vitamin D Tests Aren't Needed for Everyone, Panel Says

From the article:

"The effect of vitamin D levels on health outcomes is difficult to evaluate," the recommendation statement says.

Well, that's certainly uncertain. But if you've been following the controversy over vitamin D, you know that it's far from the only uncertainty.
As the USPSTF report notes:
  • There's no agreement on what's considered a vitamin D deficiency. Different professional societies set different minimum levels, ranging between 20 and 30 nanograms per milliliter of blood.
  • Test results can be hard to interpret, because there are lots of different types of tests and no internationally recognized reference standard.
  • Ethnicity may make a difference in vitamin D levels; African-Americans typically have lower levels, but it's not known if that's deficient or OK.

In other words, there is still a lot that we don't know about vitamin D.  Certainly we don't know enough to know when -- or whether! -- we really ought to be recommending that people take supplements.

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