Ester-C® (Buffered Calcium Ascorbate Vitamin C — American Health)

Ester-C® is a patented form of vitamin C built around calcium ascorbate plus small amounts of naturally occurring vitamin C metabolites. Because it is buffered (pH-neutral), it is gentler on the stomach than regular ascorbic acid, and the metabolites are marketed to support retention of vitamin C in white blood cells.

Ester-C is researched primarily for Immune Support. Because it is buffered with calcium, Ester-C is easier on the stomach than plain ascorbic acid, making it a good option for people who get heartburn from regular vitamin C.

The clinically studied dose is 500 to 1000 mg of vitamin C per day. Always follow the product label and check with a healthcare provider for personal advice.

For most healthy adults, Ester-C is well tolerated at studied doses. Reported effects can include: Generally well-tolerated — gentler on the stomach than ascorbic acid. Very high doses can still cause loose stools or digestive upset. It may also interact with some medications. Ester-C is not right for everyone, so check with a healthcare provider first if you are pregnant or breastfeeding, have a medical condition, or take prescription medication.

Possible interactions include: Iron supplements — vitamin C increases iron absorption, which can be helpful or excessive depending on needs. Certain chemotherapy drugs — high-dose vitamin C may interact; consult an oncologist. If you take prescription medication, check with a pharmacist or doctor before using it.

NutraSmarts rates the evidence for Ester-C as Moderate (3 out of 5). It is backed by 1 clinical trial and 1 cited reference summarized on this page. A higher rating reflects more, larger, and better-designed human studies.