When vitamin C is ingested, the body converts it into various substances. One of these is L-threonic acid. Most people consume vitamin C as ascorbic acid. But ascorbic acid passes out of the bodyquickly in urine, so little of it is absorbed. It also can cause gassiness, bloating and diarrhea.Ester-C® is different. It neutralizes intestinal acids so that it can be absorbed without discomfort. It also contains calcium threonate, the calcium salt of L-threonic acid, which enhances its absorption.One study suggested that Ester-C® acts directly on cell membranes. Another study showed that 24 hours after supplementation with Ester-C®, the white blood cells of subjects who had taken Ester-C® had absorbed more vitamin C than the white blood cells of subjects who had taken regular ascorbic acid.