Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2007
Publication Date: 10/1/2007
Citation: Abrams, S.A., Hawthorne, K.M., Aliu, O., Hicks, P.D., Chen, Z., Griffin, I.J. 2007. An inulin-type fructan enhances calcium absorption primarily via an effect on colonic absorption in humans. Journal of Nutrition. 137(10):2208-2212.
Interpretive Summary: We were interested in learning how prebiotics cause more calcium to be absorbed by the body. Prebiotics are carbohydrates that have functional benefits for gut health. We studied a group of young adults and measured the rate at which calcium was absorbed before and after they had been adapted to the prebiotic. We then calculated where in the gut the increase in calcium occurred after being treated with 8 weeks of prebiotics. We found that about 70% of the increase in calcium absorption occurred in the colon. Since calcium is not usually absorbed well from the colon, this could be an important way of increasing calcium absorption both in healthy people and those who have bowel problems.
Technical Abstract: Calcium absorption efficiency and bone mineral mass are increased in adolescents who regularly consume inulin-type fructans (ITF). The mechanism of action in increasing absorption is unknown but may be related to increased colonic calcium absorption. We conducted a study in young adults designed to evaluate these mechanisms with a kinetic technique using (42)Ca orally and (46)Ca dosed i.v. Those who responded to 8 wk of supplementation with 8 g of a mixed short and long degree of polymerization ITF by increasing their calcium absorption had kinetic measurements analyzed to evaluate the time course of absorption. The area under the curve of the oral tracer in the blood during the 26 h after dosing was calculated and the time dependence of increased absorption determined. Eight young adults (of 13 studied), with mean calcium intake approximately 900 mg/d, responded to the ITF with an increased calcium absorption of at least 3%. In responders, absorption increased from 22.7 +/- 11.3% to 31.0 +/- 15.3%. Colonic absorption, defined as absorption that occurred >7 h after oral dosing, represented 69.6 +/- 18.6% of the increase, or 49 +/- 28 mg/d. These findings suggest that in those who respond to ITF, its effects on calcium absorption occur principally in the colon. This benefit to ITF may be especially important when absorption in the small intestine is impaired for anatomic or physiological reasons.