We are made up of the vitamins and minerals found in multi's. even though they are synthetic, they are 'natural' to our bodies because we recognize the chemical structure. Multi's and other more specific vitamins are designed to round out your overall health picture.
If you are doing everything else correctly, then you will benefit from these multi's, etc. Every positive study i have seen is well conducted. The negative ones are most often, fatally flawed, where a scientist or group wants to make a name for itself with the puiblicity that a negative campaign generates. Keep in mind that everyone is aiming to gun down all the science behind vitamins, but only a few negative studies make it to t.v. on the slow news days/cycles.
WE ARE dependant upon vitamins. That is called nutrition. We prepare our foods in bad ways (microwave, lengthened storage) that lessen the nutritional content of many foods.
Personally, i take a Vitamin B complex. I largely feel that the B vitamins act as cofactors that help pull the nutrients out of the foods that you do eat.
I also take Vitamin C 100mg twice a day (it is very water soluable) and a 400U vitamin E. I also take a magnesium & potassium tablet. sometimes i will add a zinc and/or selenium to round out my antioxidant regimen.