The present invention relates to compositions of an active pharmaceutical compound or nutritional ingredient with one or more buffering agents between a pH of 1.0 and 6.0, preferably 2.0 and 4.0. The buffering agents are constituted to maintain or reduce the pH of the duodenal fluid in the proximal, mid and distal duodenum. The present invention further relates to methods of improving the absorption of an iron compound or an active pharmaceutical compound within the small intestine. The present compositions and methods improve absorption or bioavailability of the administered compositions.
