It varies a lot by nutrient, form, dose, and whether the person is deficient, but the short answer is: some synthetic vitamins/minerals are absorbed about as well as natural ones, while others are less well utilized unless the form is chosen carefully.pmc.ncbi.nlm.nih+2General ruleWater-soluble vitamins like vitamin C and many B vitamins are often absorbed well in synthetic form, and in human studies synthetic vitamin C has shown no meaningful difference from natural vitamin C at steady state.pmc.ncbi.nlm.nihMinerals can be absorbed anywhere from about 25% to 90%+, depending on the mineral and the chemical form; for example, calcium is often around...