If you eat at least five servings of fruits and vegetables per day, you probably get well over the recommended amount of vitamin C from your diet, usually in the form of ascorbic acid. Women need 75 milligrams of vitamin C per day, and men need 90 milligrams. Calcium ascorbate is another form of vitamin C sometimes found in supplements or as an ingredient in processed foods. Your doctor can advise you on whether you should take vitamin C supplements, and if so, which type would be best for you.
Differences in Composition
Supplements consisting of ascorbic acid contain 100 percent vitamin C. Calcium ascorbate, on the other hand, is a combination of calcium and ascorbic acid, so it provides about 890 to 910 milligrams of vitamin C in the form of ascorbic acid per 1,000 milligram supplement, with the remaining 90 to 110 milligrams coming from calcium.
Differences in Absorption
Ascorbic acid supplements are absorbed just as well as the ascorbic acid that is naturally present in foods, according to the Office of Dietary Supplements. Both the calcium and the vitamin C from calcium ascorbate are well absorbed. A popular vitamin C supplement containing calcium ascorbate and small amounts of other forms of vitamin C claims it is better absorbed than supplements containing just ascorbic acid, but the evidence for this is conflicting.
Best for Reducing Side Effects
If regular ascorbic acid supplements cause you to experience side effects, such as diarrhea, upset stomach or heartburn, calcium ascorbate may be a better option because the calcium helps buffer the acid. There isn't, however, strong evidence one way or the other that this reduces side effects.
If you choose calcium ascorbate supplements, make sure they don't push your calcium intake over the tolerable upper intake level of 2,500 milligrams per day when you take into account the other foods and supplements you're consuming.
Don't consume more than the tolerable upper intake level of 2,000 milligrams of vitamin C per day unless advised to do so by your doctor. This could cause adverse effects, including stomach cramps, nausea, diarrhea and a reduction in the absorption of copper and vitamin B-12. If you have hemochromatosis, it could also make your condition worse because vitamin C increases iron absorption.
High intakes of vitamin C may increase blood sugar levels and heart disease risk for diabetics, and vitamin C may also interact with NSAIDs, antacids, blood thinners, the antibiotic tetracycline, chemotherapy medications and protease inhibitors.