Any doctors/biochemists in the house? (Vitamin D absorption)

[Al B. Sure!]

I follow a fitness/health philosophy called Crossfit and Crossfitters usually praise fish oil and Vitamin D supplementation to levels I've never seen recommended before (fish oil: 3-5 GRAMS/day; Vitamin D: 5,000 IU/day; compare: the USDA recommends 200 IU/day of Vitamin D).

Now most of the evidence is anecdotal or references Soviet Bloc-era athletes and more legitimate studies, of which there are not many, seem to indicate that the 200 IU recommended by the USDA is far too low and 1000 IU may be more appropriate, although there is not much literature on this topic, especially not with regards to the benefits to physically active people.

Most of the research seems to originate from the Vitamin D Council which has an obvious bias.

My question is two-fold: one, is it likely that supplementation to such levels may provide health benefits, especially in the context of athletes, and two, perhaps more importantly, is the body even capable of absorbing such high daily levels of Vitamin D or is such supplementation mostly wasted?

[loinburger]

You're white, you'll get plenty of vitamin D just by being out in the sun.

[N35t0r]

Is vitamin D or A that was fat-soluble and liable to kill you in high doses?

http://en.wikipedia.org/wiki/Vitamin_d#Overdose_by_ingestion

[loinburger]

Both are fat soluble, Vitamin A will turn your skin orange if you eat too much of it, not sure about Vitamin D

[Heraclitus]

You're white, you'll get plenty of vitamin D just by being out in the sun.

Tehnically he is Middle Eastern.

Also he may be a player of WoW.

[loinburger]

His "race" is unimportant you buttnugget, his skin color is what matters here.

[OneFootInTheGrave]

Exposure to sunlight for extended periods of time does not normally cause vitamin D toxicity.[68] This is because within about 20 minutes of ultraviolet exposure in light skinned individuals (3–6 times longer for pigmented skin) the concentrations of vitamin D precursors produced in the skin reach an equilibrium, and any further vitamin D that is produced is degraded.[72] According to some sources, endogenous production with full body exposure to sunlight is approximately 250 µg (10,000 IU) per day.[68] According to Holick, "the skin has a large capacity to produce cholecalciferol"; his experiments indicate that

levels of 50k IU over several months can be toxic. that is with "all knowing and non-fallible wiki"...

tidbit

http://www.ncbi.nlm.nih.gov/pubmed/10232622

[Japher]

I think I just saw a vitamin D warning a few weeks ago. We watch it because my son drinks fortified rice milk.

[Al B. Sure!]

No, toxicity is not a factor at 5000 IU. The USDA's upper limit is 2000 IU but what legitimate research I've seen indicates that that upper limit is probably too low. Regardless, from Merck: (http://www.merck.com/mmpe/sec01/ch004/ch004k.html)

In adults, taking 1250 μg (50,000 IU)/day for several months can produce toxicity

No one is suggesting 50K IU/day, but rather 1/10th of that amount. Clearly, 5000 IU/day is not anywhere near toxic.

(which makes you wonder why the USDA's recommended upper limit is comparatively so low)

I suppose this does mean that Vitamin D can be absorbed at these levels, because, presumably it is being absorbed at 50K to produce toxicity.

[Al B. Sure!]

As for the sun, full body exposure maxes out at 10,000 IU but we rarely get full body exposure.

[Kitschum]

You're a healthy young man, not old, female and brittle or pregnant. Keep in mind most research on vitamin D supplements is probably made on some combination of the latter groups. Are you also taking Ca supplements?

If you're concerned about toxicity perhaps you can test your serum 25(OH)D.

[Dinner]

It's true. Just go out in the sun for 20 minutes and you'll get all the Cit D you need. Bonus points if you get naked and try to start fights with people on the street.

[Dinner]

Tehnically he is Middle Eastern.

Also he may be a player of WoW.

That means he's probably a rather pasty mideasterner.

[Heraclitus]

His "race" is unimportant you buttnugget, his skin color is what matters here.

I was nitpicking. Hence the WoW reference to people who don't spend any time in sunlight.

[Dinner]

Don't bother with him. He likes being outraged.