jamboo said:
all that told me was that some people think Centrum sucks, and that some people think it's good.
has there been any research showing that it isn't absorbed well by the body?
There have been many studies done regarding bioavailability (how well something is absorbed by the body) but they are almost never done on a per brand basis (esp. since brands offer different formulas, and often reformulate).
What you have to do is to look at the form of either the vitamin or mineral on the brand that interests you, and then you can quickly search and find the relevant studies.
Some of the worst types for bioavailability (and I believe the cheapest for makers to produce as well):
magnesium - magnesium oxide
calcium - calcium carbonate
The best and most bioavailable form for most minerals is usually done via chelation, or the binding of the mineral with an essential amino acid. Your body readily absorbs amino acids, so by binding, they can get the mineral to pass through the intestinal wall and into your blood, for use by your body. However, within chelation, you have other issues including degradation during actual creation, processing and stomach acids (e.g. all chelated forms are not the same for bioavailability).
Albion nutraceuticals is the clear winner in terms of bioavailability due to their dipeptide chelation and proven studies showing they are the most bioavailable form. They've also got roughly 40 patents in this area - they license their products to various vitamin and mineral makers, so you can look for it.
A lot of vitamin makers play the "label effect" which is they just use the cheapest materials to pop some numbers on the side of the package. But 525 mg of magnesium *oxide* is not nearly the same as 525mg Albion dipeptide chelated magnesium. You might hypothetically absorb 95%+ of the Albion version vs. 10% of the magnesium oxide....so even though it looks the same on the label, you really have to factor in whats getting into your blood, vs. what is just passing through your digestive tract and into the toilet.
One a related note, you also have to factor dissolvability of the actual tablet or capsule. If they don't use a good delivery method (reasonable binders with tested dissolution rates), the tablet can literally pass through you undissolved, in which case it really didn't matter what the contents where, they didn't help you.