The vitamin D claim is misleading. Sure, most people have enough vitamin D for bone health. But vitamin D does a lot more than make your bones healthy, so supplementation is still probably useful. Luckily, unlike vitamin C, too much vitamin D is not harmful so all you're wasting is money if the other claims for vitamin D also get disproved.
The biggest Vitamin D supplements I've seen have 1000 IU per tablet, and the bottle suggests one tablet per day. According to the article you linked, 10,000 IU/day is safe (we can get that much from sunshine in a day), and long-term overdose has been observed at 77,000 IU/day. You'd have to go pretty hog-wild with the Vitamin D supplements to overdose.
For what it's worth, I supplement using the 5000 IU pills taken at about 7/week (irregularly, making up doses as necessary). I recently had my blood tested for D3 levels, and found it was close to but not exceeding the standard recommended level.
That article is just about Hypervitaminosis D, other harmful effects are possible (depending on the individual) when supplementing at high levels like 10,000 IU/day.
Did anyone else find themselves clicking on that link very cautiously? Wikipedia should really institute some sort of official warning system for articles with shocking medical images.
What mechanism are you talking about? The main mechanism for Vitamin D that I know of is to limit creation from sunlight. But if one takes supplements without any caution as you seem to suggest then one is bypassing it.
Supplementing vitamin D is a great idea (I do it), but it is dangerous for those that are naive about it and think there is no risk.
I agree that is seems misleading. I was diagnosed with vitamin D deficiency. Which maybe isn't that surprising that on the average day I might have gotten no sun at all,and don't eat foods like fish, eggs, butter.
Now I do make a point of a midday walk and a vitamin D supplement. Severe vitamin D deficiency can be pretty yucky.
