Why do cheap calcium supplements work as well as expensive ones?

Why do cheap calcium supplements work as well as expensive ones?
Price differences in calcium supplements largely reflect marketing, not efficacy. Basic calcium carbonate, at roughly 40% elemental calcium, is cheap and effective for those with normal stomach acid. Organic forms like calcium citrate cost more but only help those with low gastric acid. Claims of 90% absorption rates are misleading—such figures come from studies on severely calcium-depleted animals, not normal human diets. Human absorption is tightly regulated: it rises when deficient, falls when adequate. A landmark 1989 New England Journal study found no statistically significant difference in absorption among calcium salts in healthy people. Single doses above 500 mg actually reduce absorption efficiency. For most buyers, a 6 yuan bottle of calcium carbonate works as well as a 600 yuan premium product.