Jake Young is a 
Over at the NYTimes Well blog they have a really good summary of studies about vitamins and improvements to health.
Everyone needs vitamins, which are critical for the body. But for most people, the micronutrients we get from foods usually are adequate to prevent vitamin deficiency, which is rare in the United States. That said, some extra vitamins have proven benefits, such as vitamin B12 supplements for the elderly and folic acid for women of child-bearing age. And calcium and vitamin D in women over 65 appear to protect bone health.But many people gobble down large doses of vitamins believing that they boost the body's ability to mop up damaging free radicals that lead to cancer and heart disease. In addition to the more recent research, several reports in recent years have challenged the notion that megadoses of vitamins are good for you.
Read the whole thing.
Everyone knows that you need certain levels of vitamins to stay healthy, but over the last years -- particularly in reference to antioxidants -- there has been all this bold and, in my opinion, overblown comment about how supranormal doses of vitamins may be helpful. But the data just isn't there, and in some cases supranormal doses of vitamins have been linked to small increases in mortality.
We are not living in sub-Saharan Africa where you might see blind children do to vitamin A deficiency. In clinical settings, the two most common types of patients with vitamin deficiency are alcoholics (or drug users) and the frail elderly. (With the frail elderly, you sometimes hear about people coming in with vitamin deficiency from a "tea and toast" diet.) Pregnant women definitely need to make sure they have enough folate, and calcium and vitamin D help prevent bone loss in old age. But past that, for the majority of healthy people vitamin supplementation is unnecessary.
Now industry groups and vitamin enthusiasts might respond that these studies were simply not equipped to detect the good effects of supplementation. The effect sizes may be small. (She mentions this at the end of her post.) But you have to wonder whether if the effect sizes of benefits for supplementation are so small that we have repeatedly failed to detect them, they may not be there at all. And no one debates that vitamin supplementation is necessary for key groups of patients. What is under dispute is whether as a public health strategy all people should take vitamins.
For my part, I think it is mostly a waste of money.
Medicine & Health
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But there must be a region that is above the minimum to prevent deficiency, and where supplementation is valuable.
Given the extremely low cost of vitamins, it seems like there must be a cost-effective region.
The general opinion of the dietitian community is that a multivitamin is the most cost effective health insurance you can get.
Posted by: Joseph | November 23, 2008 11:06 PM
I wonder about young children (like the kind I have--6 and 3). Our pediatrician recommended iron supplements. The 6 year old is a picky eater, so we just give both them multi vitamins with iron. It is not cheep (though not overly expensive). But I often wonder if it is a waste. Except for the iron, I suspect it is.
Posted by: ropty | November 24, 2008 10:09 AM
Joseph,
But if the effects of supranormal doses of vitamins are too small to detect in most cases, why would smaller amounts be of any value whatsoever?
And yes, the dietitian community believe that, but belief is not enough.
Posted by: Jason Dick | November 24, 2008 10:40 PM
Jason -- IANADoctor, but the short answer (as I understand it) is, the human body only needs certain levels of vitamins, above which it either doesn't absorb well, or the overdose is actually counterproductive and detrimental to health.
There are some interesting interactions between foods & vitamins as to what gets absorbed. I discovered that when I was diagnosed with uncomplicated iron-deficiency anemia. The doctor not only put me on iron supplements, she also went over various aspects of my diet and supplementation schedule with me, pointing out the rather complicated interactions iron absorption in the intestine has with vitamin C (good, mostly), calcium (calcium being necessary in small amounts, but apparently inhibits iron absorption in large amounts, so when I was taking an iron supplement with a calcium supplement I essentially wasn't getting the iron), possible interactions with some B vitamins, and caffeine (bad stuff, caffeine, apparently).
With some substances, taking more means you get less through the wall of the intestine, counterintuitively -- or it can inhibit the absorption of other necessary nutrients. And that is aside from the effects of simple overdose.
In short, there isn't a straight linear relationship between the amount of something we ingest and the effect it has. There is often a bell-curve of potency or efficacy -- and if you go off the high end of the curve, you are still off the curve.
Posted by: Luna_the_cat | November 27, 2008 7:50 PM