Scientists pinpoint inulin's calcium absorption site

By Stephen Daniells

- Last updated on GMT

Related tags Calcium absorption Osteoporosis Small intestine

The ability of prebiotics inulin and oligofructose to enhance
absorption of calcium in the intestine is focussed in the colon,
suggests a new study with young adults that backs up animal

The research, published in the October issue of The Journal of Nutrition , improves our understanding of the ingredient, and may aid the development of other products, suggested the researchers, led by Steven Abrams.

"This study provided confirmation that the animal studies, which had identified a benefit of [inulin-type fructan] ITF for calcium absorption, accurately identified the principal mechanisms as well," wrote the authors, from Baylor College of Medicine (Houston), the USDA/Agricultural Research Service Clinical Nutrition Research Center, and Texas Children's Hospital.

"Furthermore, understanding the site of action may be helpful in considering the effects of ITF and related products on the absorption of other minerals or on the design of other ITF products," they added.

The research appears to confirm the potential of the ingredient to support bone health and prevent osteoporosis, estimated to affect about 75m people in Europe, the USA and Japan.

Currently, two approaches are being pursued to prevent osteoporosis:

First, optimise bone mass acquisition during adolescence, and secondly, minimise bone loss after the menopause.

The majority of work with inulin and oligofructose to date in both animals and humans has focussed on the first approach, with animal studies in particular showing repeatedly over the last decade that inulin/ oligofructose supplementation to a diet results in more absorption of calcium.

"The mechanism of action in increasing absorption is unknown but may be related to increased colonic calcium absorption," stated the authors.

Abrams and co-workers recruited 13 young adults (average age 23.8, average BMI 21.9 kg per sq. m) and assigned them to eight weeks of supplementation with eight grams of a inulin-type fructans (Beneo Synergy 1, Orafti).

The subjects underwent a calcium isotope study (42Ca orally, and 46Ca intravenously) before and after starting the prebiotic supplementation.

Eight of the subjects (average calcium intake of 900 mg/d) were reported to have responded to prebiotic supplementation, with increased calcium absorption of at least three per cent, from 22.7 to 31.0 per cent.

Seventy percent of the absorption increase was found to have occurred in the colon, said the researchers.

This is equivalent to a 49 mg per day being absorbed in the colon.

"Given the multiple methods by which ITF acts, it is not surprising that some human subjects have a much greater response than others.

Our results demonstrate that in those individuals who respond to ITF, its effects primarily occur in the colon," they stated.

They added, however, that while increased solubility of calcium in the colon appears to be the predominant mechanism for IFT, whole gut mechanisms must not be ignored.

"In this regard, it is important to remember that in humans, calcium absorption primarily occurs in the upper portion of the small intestine compared with the large intestine in rats," stated Abrams and co-workers.

The study is in-line with studies with human adolescents, where short-term supplementation with the synergistically active mixture of oligofructose and long-chain inulin (SYN1) is reported to have a higher calcium absorption (38 per cent), than the placebo group (32 per cent).

These increases in calcium absorption were subsequently repeated by long-term supplementation studies of up to a year in length.

Indeed, one study reported that girls and boys aged between 9 and 12 supplemented with SYN1 had an additional net accretion of calcium of 30 milligrams per day, compared to the controls who received a placebo ( American Journal of Clinical Nutrition , 2005, Vol. 82, pp.


Belgium's Orafti has been influential in building the science behind inulin and oligofructose, backing research into potential benefits for a variety of health conditions ranging from bones to colorectal cancer, from immunity to satiety and weight management.

The company co-funded the current study, along with the USDA Agricultural Research Service and the National Institutes of Health.

Source: Journal of Nutrition Volume 137, Pages 2208-2212 "An Inulin-Type Fructan Enhances Calcium Absorption Primarily via an Effect on Colonic Absorption in Humans" Authors: S.A. Abrams, K.M. Hawthorne, O. Aliu, P.D. Hicks, Z. Chen, I.J. Griffin

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