It's not as simple as popping a single whopping pill to get all your vitamin and mineral needs:
For instance, vitamins A, D, E, and K are all fat soluble. Meaning, if you're getting it in a vitamin water, it's not going to absorb unless you are having some kind of fat to go with it. But these are also the most likely to be overdosed.
Vitamins B and C are water soluble and therefore eliminated much quicker, less likely to overdose.
Vitamin A can block absorption of Vitamin D, as in milk, so it's best to get your vitamins from multiple sources or avoid the combo. Interestingly though, A is needed to absorb calcium, again as in milk. So one one hand A blocks D, but aids Calcium. Sources of vitamin A are most yellow & orange vegetables, apricots, cantaloupe, mangoes, papaya .
Our ability to absorb B vitamins lessens with age, and may necessitate SQ injections. On top of all that, certain medications such as NSAIDS (anti-inflammatories), diuretics, anti-diabetic agents and cholesterol medicines can inhibit absorption.
B vites can be divided into :
Folate-sources include avocado, asparagus, oranges, green leaves, broccoli, oats, legumes, eggs
B1, B2, niacin and b3 (lean meats, legumes, milk, coffee, tea, fortified flours and cereals ), B5, B6 (fish, bananas, potatoes, avocado, whole grains, meats ) and B12 (which is stored in the liver. 1/4 of the population is deficient in B12.)
Anemia is usually linked to iron deficiency, but in reality it can be iron or B vitamin deficiency. While most of the population pops iron, it's actually not a great choice, it's stored in the body, easily overdosed, and can even stain your teeth. Start with the B vites, since they're water soluble, and see if that helps first, or ask your doctor to check.
(I like Emergen-C for my B vitamin supplement)
Then there is C (Many fruits and vegetables, e.g., bell peppers citrus, most berries, pineapple, papaya, cruciferous vegetables, tomato, green leaves, potato)and C-ester. C-ester is fat soluble and stored longer in the body than it's water soluble cousin C.
Vitamin K. polyunsaturated oils block K, like in salad dressing, which is interesting because vitamin K can be found in green vegetables, like a salad.
Magnesium is needed for D and E usage but 70% (!!!!) of the population is deficient.
Finally, iron absorption is facilitated by vitamin C, but inhibited by calcium. So take your iron with orange juice, and avoid the fat. Makes you wonder about fortified cereals topped with milk, doesn't it?
The point in all this? It's not a quick fix to pop a pill, or drink a vitamin water, "drink your milk" or eat your fortified cereal. There is no one-stop-shop when it comes to healthy eating.
This is just a beginner's list of what interacts with what, but it goes on. Eat a varied diet, as close to nature as possible and remember it's best to get the vitamins straight from the source (your food) than a supplement, whenever possible.