I just don't see how, with all that's taken out of processed food, enough is put back in to prevent vitamin deficiencies, especially with all nutritionless filler that makes up so much of the volume of this kind of food. I suspect anyone eating mostly processed foods is getting more than adequate amounts of certain fortified vitamins and woefully inadequate amounts of others.
Also, there is a lot of research coming along showing that what we thought were adequate levels to prevent deficiency aren't quite as adequate as we thought. It may be enough to stave off acute illnesses like rickets or scurvy, but not enough to prevent slower developing chronic diseases and attrition issues. Most fortification is done with those old targets in mind, compounding my doubts of getting real adequate levels from fortified food.
Certainly there are multi's out there that are just absolute overkill, but I don't think you can be dismissive of them in general given what we know of nutrition, what we still don't know, and the current state of our food supply.
I feel like I have been over and over and over this in this forum - and it is a testament to industry-sponsored spin and misinformation. There are a few micronutrients which intakes are suspected to be suboptimal, and these would be vitamin D, calcium, magnesium, iron (in some populations), to name a few. Of these, in my opinion, the only clear case for supplementing can be made for vitamin D, and that's because there are precious few natural sources of the vitamin - and dairy is so poorly fortified.
The "emergent research" you're citing that finds micronutrients have a role to play in disease prevention is only for SOME of them, notably vitamin K, vitamin D, magnesium, and calcium. Of these, D is probably the best researched - and I personally do 2000 IU every day. Some of the scientific support for them rests heavily on epidemiological studies, which are unable to tease out the differences in peoples' diets. All they can tell you is that intakes higher in nutrient X produced less of disease Y. In other words, there is not enough research in the majority of cases.
I also fear that you're falling into the multivitamin panacea trap. Taking a multivitamin is not going to stave off chronic disease if you aren't doing anything else right. For example, chromium has been found to help diabetics control their blood sugars, but it doesn't cure diabetes - taking chromium is not going to help you if you are gaining weight and going crazy with the carbs. People swear by vitamin C, but there is almost zero clinical evidence that it does any good to prevent any kind of disease, weak evidence that it might help lessen the duration of a cold (by maybe a half-day, at best) and the total body pool of vitamin C is around 100 mg or so, anywhere from 1/5th to 1/10th the common dosage in supplements. The fact that a lot of these supplements have no scientific evidence notwithstanding, I just don't see what a few extra milligrams of one micronutrient or another to address an alleged "deficiency" is going to do. I do see that it could slow progress at trying to get people to adopt healthier lifestyles.
There is also real, verifiable harm associated with use of supplements. Even Vitamin D, which is back in favor, can cause serious harm if overconsumed (infant formulas over supplemented with vitamin D a long time ago caused huge problems). Example: two major studies of vitamins A and E were terminated early after use of the supplements was associated with HIGHER risk for developing cancer in the study populations (these are the well-known CARET and ATBC studies). Another example: folate is a major player in DNA synthesis, and a commonly used chemotherapy drug (methotrexate) blocks the action of folate on DNA. In theory, people using multivitamins that provide mega-doses of folate could be spurring their cancer along without knowing it. This was one of the major arguments raised against fortifying flours and cereals with folic acid a generation ago. Example 3: antioxidants work in the body by inactivating oxidant substances. The theory is, oxidation produces DNA damage -> cancer. So the thinking goes, more antioxidants, less cancer. So people pop C and E all day. As I've written, E was associated with higher risk for cancer. There's some theorizing that overuse of antioxidants and antioxidant vitamins may actually inhibit your body's ability to cope with oxidative stress (which, believe it or not, affects your ability to recover from exercise!).
All said and done, I really don't think that you can make a good case for supplementation in healthy populations, with the exception of vitamin D. Obviously, a multivitamin for pregnant women is a good idea, in the elderly, infants, etc. But I don't see a multivitamin making any major contribution to preventing chronic disease in the absence of major lifestyle changes, and very little scientific support that doses above current levels for a majority of micronutrients is actually beneficial. I'm having a hard time seeing the upside to their use besides contributing to a supplement company's bottom line, and it just seems to encourage complacence. As I've said, there is a huge potential downside to them as well measured not in dollars, but in health.
Cliffs notes:
-Limited to no scientific evidence to justify large doses, except for vitamin D. A multivitamin is not going to prevent you from getting chronic diseases if you treat your body like garbage, and is marketed as a panacea. Documented downsides to vitamin use, such as an increased risk of cancer in susceptible populations with use of vitamins A and E, and plenty of other theoretical drawbacks. Conclusion: the "cheap insurance" theory just doesn't hold water.
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