SISU Ester-C - Fact Sheet - 24-Hour Immune Support

Sep 8, 2026

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SISU Ester-C is a patented, pH-neutral form of calcium ascorbate created by buffering vitamin C with calcium. The formula is designed to deliver active vitamin C metabolites that support quick absorption and biological functions similar to vitamin C, including skin, joint, vision, cardiovascular support, antioxidant protection, and iron absorption. Claims are reinforced with summarized scientific studies on longer white blood cell retention, improved absorption and urinary loss profiles, and better tolerance versus regular ascorbic acid, including fewer respiratory infections.

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SISU Ester-C Fact Sheet

What is Ester-C?

What makes SISU Ester-C better than other vitamin C?

Studies supporting the claims

Ester-C Research Summary

SISU Ester-C® Fact Sheet • 24-Hour Immune Support • Quick Absorption • Backed by Science • Gentle on the Stomach [sisu.com](sisu.com) • 1.800.663.4163 What is Ester-C® ? • Ester-C® is a unique and patented form of calcium ascorbate, which is created when ascorbic acid (vitamin C) is buffered with calcium. • Ester-C® takes calcium ascorbate and, using a proprietary, water-based manufacturing process, produces a pH neutral product that contains active vitamin C metabolites (that do not exist in any other form of vitamin C, including calcium ascorbate) . • These natural metabolites provide quick absorption. • Ester-C® also functions biologically like other forms of vitamin C, providing benefits for skin, joint and vision health, cardiovascular support, antioxidant protection, iron absorption, anti-inflammatory and immune system wellness. What makes SISU Ester-C® better than other vitamin C? • The natural metabolites study showed longer retention than any other form of vitamin C. • It offers 24-hour advanced immune support. • It is easier on the stomach than ordinary vitamin C, or ascorbic acid. • Ester-C® is a less acidic and more digestible form of vitamin C. • While other calcium ascorbates are also easy on the stomach, they aren’tas bioavailable; one study discovered that the absorption rate of regular calcium ascorbate was half that of Ester-C® . • It was the first ever vitamin C to receive a patent. (April 18, 1989) Are there any studies that back up these claims? • Yes, Ester-C® is backed by science. • The patented Ester-C® has been scientifically proven to increase vitamin C absorption.1 • Ester-C® is retained in white blood cells longer than ascorbic acid (up to 24 hours.)2 • Studies show that there is less vitamin C loss in urine with patented Ester-C® and that it remains active in the white blood cells for 24 hours.3 • In one study, taking Ester-C® resulted in fewer respiratory tract infections and those who did get sick recovered faster and were much less likely to develop a second respiratory infection vs. placebo.4 • Ester-C® is less acidic and easier on the stomach than ascorbic acid.5 See over for study details. and Ester-C® are licensed trademarks of The Ester C Corp. U.S. Patent Nos. 4,822,816, 5,070,085 and 6,197,813 . ~~ ~~ Ester-C® Research Summary | 1. Verlangieri, Anthony. Acute study to determine the Relative Rate of Absorption and Excretion of U.S.P. Calcium Ascorbate and Ester-C® Calcium Ascorbate. 1988.
A study comparing Ester-C® Calcium ascorbate to U.S.P. (United States Pharmacopoeia) calcium ascorbate determined that the structure of Ester-C® is unique and differs from USP calcium ascorbate. This study discussed how Ester-C® is absorbed more rapidly than calcium ascorbate.
2. Bernal, S. et al. Vitamin C uptake in White Blood Cells in Vivo. 2006.
Bernal, [S. et](S. et) al: comparison of white blood cell levels of ascorbate after oral use of 1000 mg of either Ester-C® or regular ascorbic acid.
3 groups of 5 people (15 subjects total, all adult men ages 21-50) received one of the vitamin C preparations or placebo, followed by a washout period of 6 days and then were given one of the other treatments until they had been tested in all 3 groups. After taking supplements, blood samples were collected at 1,2,3,4,8 and 24 hours. Vitamin C levels were determined in plasma and white blood cells (WBC) . There was no significant difference in the uptake of different forms of vitamin C into plasma or WBC; however, there was a difference in the retention of vitamin C in WBC. Ester-C® was retained in white blood cells longer than regular ascorbic acid and this was apparent 24 hours after administration.
3. Wright, Jonathan et al. A Human Clinical Study of Ester-C® vs. L-Ascorbate Acid. 1987.
A study in 12 adults. Participants were placed on a low vitamin C diet for 1 week and then received either ascorbic acid or Ester-C®, 3000 mg. White

FAQs

What is SISU Ester-C made from and why is it unique?

Ester-C is a patented form of calcium ascorbate made by buffering ascorbic acid (vitamin C) with calcium. A proprietary water-based process produces a pH-neutral product containing active vitamin C metabolites.

How does Ester-C support immune function?

Ester-C is positioned as offering 24-hour advanced immune support. Studies summarized in the fact sheet report longer retention of Ester-C in white blood cells and continued activity for up to 24 hours.

Is Ester-C easier on the stomach than regular vitamin C?

The fact sheet states Ester-C is less acidic and more digestible than ascorbic acid, with clinical evidence summarized on better tolerability and fewer gastric discomfort effects compared with regular ascorbic acid.

Sep 8, 2026

Upload by Skyler