Vitamin C Absorption
Chester J. Zelasko, Ph.D. | September 14, 2004

Here at Better Life Unlimited, we’ve recently received lots of questions about the forms and absorbability of vitamin C. This Newsletter will address those issues, but before I begin, some background information is necessary about research on the digestibility and absorption of nutrients.

Research Types
There are at least three types of studies that are typically utilized in this type of research. The first is called in vitro. Essentially, some cells from animals or humans, usually white blood cells, are placed in a test tube. The cells are washed with a given amount of the vitamin; then the cells are examined to see how much of the vitamin has been absorbed.

There are also two types of in vivo research that use either animal models or humans. The animal or human subjects consume a measured quantity of the vitamin. Blood, urine, and other excretions are examined to determine how much of the vitamin is absorbed.

There are inherent problems with both types of research. In vitro research can provide information only on the absorption of the nutrient when the cells are directly bathed in the vitamin. While important as a preliminary step, there is no indication that this will occur in the body where other body processes may affect absorption by the tissue.

With in vivo research using animals, the animal may metabolize the vitamin in different ways than humans do. With humans, absorption into the blood stream and then into either red or white blood cells may or may not indicate that the vitamin is absorbed into other tissues. The only way tissue absorption is directly measurable is by biopsy of the organs, which is often cost prohibitive or ethically prohibitive. Excreted metabolites are often used as an indication of absorption, but without direct measurement, there’s no proof that absorption is or isn’t happening.

Given the issues surrounding this type of research, caution should be exercised when extraordinary claims are made about the digestion, absorption, and utilization of various forms of nutrients. The amount of research required to prove claims is extensive and often cost prohibitive.

Vitamin C Absorption
Vitamin C is typically found in food and supplements in the form of L-ascorbic acid. Research has demonstrated that whether from food or supplement, vitamin C is absorbed readily into the blood stream after ingestion. Another delivery system has been developed for vitamin C in which the vitamin C is combined with mineral salts, such as sodium or calcium. There are at least three claims made for mineral ascorbates, the term used when vitamin C is combined with minerals.

Claim 1: Mineral ascorbates are better absorbed than ascorbic acid.
In the study cited most often, 12 subjects were given very high doses (over 2 grams vitamin C) of a mineral ascorbate, ascorbic acid, and citric acid (1). The study reported that the mineral ascorbate was significantly better absorbed at various times after administration than ascorbic acid alone.

However, the results are reported as percentages. Without knowing the absolute numbers, we don’t know whether the increased absorption into the bloodstream is clinically significant or not. At least one animal study supports the human trial, while another does not (2-3). The real problem is the lack of further human trials. Claiming increased absorbability on the results of 12 subjects is not exactly overwhelming.

Claim 2: Mineral ascorbate is better absorbed into cells than ascorbic acid.
The supporting research either is drawn from in vitro studies or examines only certain types of blood cells after consumption of mineral ascorbates and ascorbic acid (1). As mentioned earlier, the problem is the assumption that the vitamin will be absorbed equally by all tissues in the animals. There is no evidence to support that conclusion.

Claim 3: The mineral ascorbates cause less stomach upset at high doses than ascorbic acid alone.
This may be valid. Minerals such as calcium may act as a buffer so that the vitamin C is less problematic for those with sensitive stomachs. While there is no research to support the direct claim, it seems to make sense and in time research may prove it true.

The Bottom Line on Ascorbates
What does all this mean? At least two things. First, while every claim about mineral ascorbates may prove to be true, there is little evidence to support the claims at this time. That doesn’t make the evidence bad--just incomplete.

Second, L-ascorbic acid seems to provide the body with an adequate amount of vitamin C to support your health. If it causes you distress, it may be prudent to take it with your calcium supplement to reduce stomach upset. There seems to be little reason to change to another source of vitamin C.

The presence of phytonutrients with vitamin C may prove to be important, but that’s a Newsletter for another day.

  1. Wright, JV and Suen, RM. Comparative Studies of “Ester C” Versus L-Ascorbic Acid. International Clinical Nutrition Review 1990; 10(1).

  2. Bush MJ, Verlangieri AJ. An acute study on the relative gastro-intestinal absorption of a novel form of calcium ascorbate. Res Commun Chem Pathol Pharmacol. 1987; 57(1):137-40.

  3. Wang S, et al. Pharmacokinetics in dogs after oral administration of two different forms of ascorbic acid. Res Vet Sci. 2001; 71(1):27-32.
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