Resolving the Vitamin D-Bate

Is there a way we can ask the body how much vitamin D it wants overall? Scientists came up with two ways. First, let’s say you give a whopping dose, and I mean whopping: 100,000 IUs, something that could be toxic if done on a daily basis. The question is, what’s our body’s saturation point?

Of this massive dose, how much does our body actually use, and how much does it sock away in storage for use later on down the road? Here’s the graph: 30 people, followed for four months after the megadose. Here’s the flood of D coming into their system. But the solid circles represent the pool of vitamin D our body is keeping in our bloodstream for activation, and the rest is likely stored away to be used on an as-needed ongoing basis.

Note that in this setting of abundance, the body is keeping our levels right around that sweet spot dip found in the U-shaped mortality curve.

You can do the same thing at the other end of the spectrum, too. Instead of a megadose, you can start by giving really tiny doses and gradually work your way up. When you do, you get a graph like this, showing a so-called biphasic pattern: really steep at first, but then leveling out.

When you take in just a little bit, your body zips it into circulation, desperately needing it. But then, as you increase the dose, at a certain point you kind of turn the corner. When the crisis is averted, your body seems happy enough with your levels that as you take more in, your levels still rise, but it’s not such an emergency.

Now if this plateau were flat, completely horizontal, then there’d be no risk of toxicity. But because your body can’t help but let some in, your levels continue to rise with increasing intake, and you can run into vitamin D toxicity problems if we take too much.

But what’s this level here, right at the corner, where your body takes a big sigh of relief that you’re doing pretty good on vitamin D?

Working in from both ends, the level at which our body appears satisfied translates to about 2,000 IUs a day, which should get us right into that U-shaped longevity sweet spot—whereas the Institute of Medicine recommendation appear too low, and the 10,000 IU recommendation put forth by others appears too high.

To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by veganmontreal.

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• Heaney RP, Armas LA, Shary JR, Bell NH, Binkley N, Hollis BW. 25-Hydroxylation of vitamin D3: relation to circulating vitamin D3 under various input conditions. Am J Clin Nutr. 2008 Jun;87(6):1738-42.

Image thanks to plant nutrition via Flickr

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• suplementos de vitamina D