In dietary supplements, calcium, as an alkaline mineral, must pair with an acid to produce a neutral salt the body can digest. Two such salts are calcium lactate and calcium citrate. Although there are differences between the compounds, they generally serve the same purposes with a similar degree of efficacy. Applications include treatment or prevention of osteoporosis and hypocalcemia, lowering phosphorus and lowering blood pressure.
The main difference between calcium lactate and calcium citrate is the acids they contain. Whereas calcium lactate contains calcium bound with lactic acid, calcium citrate displaces lactic acid for citric acid. Lactic acid has nothing to do with milk or lactose; it is a chemical muscles and blood cells produce naturally when they burn carbohydrates while having limited access to oxygen, usually during rigorous exercise. Citric acid, though sometimes mistaken for vitamin C, is an acid that appears mostly in citrus fruits and contains no vitamins or minerals. In fact, neither of these acids produce any dietary benefits or detriments when taken as part of a calcium supplement. However, they do affect the bioavailability of the calcium with which they're bound differently.
Elemental calcium is the amount or proportion of calcium in a supplement that the body can absorb. Calcium citrate is 20 percent elemental calcium, while calcium lactate is 13 percent. This difference affects the size of each respective pill, with calcium lactate being slightly larger than calcium citrate. However, given size accommodations, there are no other differences between the two salts as dietary supplements due to their differing bioavailabilities.
Both calcium citrate and calcium lactate can adequately supplement diets low in calcium. Moreover, they can provide calcium even in gastric environments with low acid. This property makes both supplements ideal for older users, as gastric acid secretion reduces with age, according to Alan Pressman and Sheila Buff in "The Complete Idiot's Guide to Vitamins and Minerals." The ease of absorption and greater bioavailability of calcium citrate makes it the best option for kidney stone treatment, Pressman and Buff indicate.
Likely due to their minor differences, calcium citrate is considered the "main" or "actual" product, while calcium lactate is regarded as the generic version, according to Pressman and Buff. Both remain relatively expensive, although the latter is slightly less than the prior. Given their easy absorption, they are marketed primarily to those who take antacids regularly.