Absorption Of Ascorbic Acid Research Articles

Permeation Enhancement of Ascorbic Acid by Self-Dissolving Micropile Array Tip through Rat Skin

Ascorbic acid (AA) loaded self-dissolving micropiles (SDMP) were prepared using chondroitin sulfate as the base for the percutaneous administration of AA. AA solution was added to dense solution of chondroitin solution, glue, and array tip, 1.0 cm(2), containing 100 SDMPs of which length was 500 microm and basal diameter was 300 microm, were prepared. Two kinds of AA array tips containing 1344.2+/-1.7 microg (high content ones) and 638.7+/-4.3 microg (low content ones) were used. In vitro dissolution study showed that more than 90% of AA were released from both SDMP array tips within 5 min. Stability experiment showed that 99.2-99.4% of AA was detected in SDMP array tips when stored at 23 degrees C for 1 week. When in vitro permeation experiments were performed after AA SDMP array was inserted to the isolated rat abdominal skin, extremely high amounts of AA, 1285.3+/-369.0 microg (95.3%) for high content SDMP tip and 405.6+/-84.3 microg (65.8%) for low content SDMP tip, were permeated for 6 h into the receptor compartment due to the break down of the skin barrier function. When AA SDMP array tip was administered to the rat skin under anesthetized condition with the different contact times, 10, 20 and 30 min, the permeated amount of AA was dependent on both the AA content in SDMP array tips and the contact time. When AA SDMP was contact to the skin for 30 min, permeated amounts of AA were 146.8+/-22.9 microg (10.9%) for high content-SDMP tip and 61.2+/-18.2 microg (9.6%) for low content SDMP tip. These results suggest the usefulness of SDMP array tip for the percutaneous absorption of AA.

Absorption of folic acid and ascorbic acid from beverages

The purpose of this study was to test for possible differences in the bioavailability of nutrients from three different beverages using a double‐blind, within‐subjects experimental design. The study tested whether the bioavailability of vitamin C (i.e. ascorbic acid or AA) and folic acid (FA) in adult men differed after ingestion of a fortified beverage (Essential VitaminWater, Glacêau®), orange juice (OJ) and 1% milk. Participants were aged 20‐35y, with body mass indexes ranging from 20‐30 kg/m2. Serum concentrations of AA and FA were assayed by serial blood draws, which were made at 30 min intervals for 4.5 hours. Results showed that the concentration profile of AA was significantly greater after ingestion of the fortified beverage compared to OJ. However, the bioavailability of AA in the fortified beverage and OJ was not significantly different, indicating that the higher serum concentration of AA in response to the fortified beverage was due to that beverage's higher AA concentration. In terms of FA, analyses indicated that serum concentration and bioavailability did not significantly differ between the fortified beverage and OJ. Research support provided by Glaceau LLC.

SVCT1 and SVCT2 Genotypes Modify the Association between Dietary Vitamin C and Serum Ascorbic Acid Concentrations in Men

Clinical trials have established that individuals have different serum ascorbic acid (vitamin C) responses to dietary vitamin C. This may be due, in part, to genetic differences. In humans, vitamin C transport proteins 1 and 2 (SVCT1 and SVCT2) are required for vitamin C absorption and uptake, respectively. Our objective was to determine if polymorphisms in the SVCT1 and SVCT2 genes alter fasting serum ascorbic acid concentrations in response to dietary vitamin C. We recruited 533 women and 235 men between the ages of 20â29 yrs who were all non‐smokers. Dietary, lifestyle and anthropometric data were obtained and blood samples collected to determine fasting serum ascorbic acid concentrations by HPLC and to isolate DNA. Real‐time PCR was used to genotype for two polymorphisms in SVCT1 (rs4257763 G>A and rs6596473 G>C); and two polymorphisms in SVCT2 (rs6139591 G>A and rs2681116 C>T). Overall, the diet‐serum correlation was significant for men (r=0.21, p<0.01), but significant correlations were only observed for the following genotypes: rs4257763GG (r=0.32, p<0.01), rs6596473CC (r=0.44, p<0.01), rs6139591GG (r=0.39, p<0.01) and rs2681116 TT (r=0.66, p<0.001). No significant associations were observed for women in any of the genotype groups. Our data suggest that the correlation between dietary vitamin C and serum ascorbic acid concentrations in men differs between the genotypes of common polymorphisms that affect the absorption and uptake of ascorbic acid. Supported by the Advanced Foods & Materials Network.

Influence of poly(ethylene glycol)‐α‐cyclodextrin complexes on stabilization and transdermal permeation of ascorbic acid

The present study was conducted to investigate the effect of poly(ethylene glycol)-alpha-cyclodextrin (alpha-CD) complexes on stabilization and cutaneous permeation of ascorbic acid from specially prepared transdermal patches. Poly(ethylene glycol) citrate (6-armPEG) and its inclusion complex with alpha-CD were prepared and used for preparation of the transdermal patches. Duro-Tak 87-2979 was taken as an adhesive matrix in combination with ascorbic acid. A diffusion cell with an artificial membrane was used to evaluate the absorption of ascorbic acid from the patches. The influence of drug release of alpha-CD and two types of its PEG complexes (as the novel permeation enhancers) was tested. The 6-armPEG-alpha-CD complex consisting of a PEG-citric acid ester at a concentration of 0.08-0.1% (w/v) is a suitable stabilizer for ascorbic acid during UV assay. The release studies showed that the type of enhancer is important in diffusion of the drug across membrane. Furthermore, the diffusion of ascorbic acid was considerably enhanced in the presence of 6-armPEG-alpha-CD complex. Inclusion complexes of 6-armPEG with alpha-CD at a concentration of 0.08-0.1% (w/v) is a suitable stabilizer for UV method of assay. The present data suggest that 6-armPEG-alpha-CD complex is also useful in enhancing the release of ascorbic acid from the acrylic type pressure sensitive adhesives.

Ferulic Acid Stabilizes a Solution of Vitamins C and E and Doubles its Photoprotection of Skin

Ferulic acid is a potent ubiquitous plant antioxidant. Its incorporation into a topical solution of 15%l-ascorbic acid and 1%alpha-tocopherol improved chemical stability of the vitamins (C+E) and doubled photoprotection to solar-simulated irradiation of skin from 4-fold to approximately 8-fold as measured by both erythema and sunburn cell formation. Inhibition of apoptosis was associated with reduced induction of caspase-3 and caspase-7. This antioxidant formulation efficiently reduced thymine dimer formation. This combination of pure natural low molecular weight antioxidants provides meaningful synergistic protection against oxidative stress in skin and should be useful for protection against photoaging and skin cancer.

Apparent absorption of eight micronutrients and phytic acid from vegetarian meals in ileostomized human volunteers

Objectives Apparent absorption of eight micronutrients and degradation of phytic acid were studied in human subjects who underwent ileostomy. The prominent factors affecting micronutrient absorption from vegetarian Indian meals ( n = 11) were identified. Methods Levels of β-carotene, ascorbic acid, riboflavin, and thiamine in food and ileostomy contents were estimated by spectrophotometry and spectrofluorometry. Contents of zinc, iron, copper, and manganese were estimated by atomic absorption spectrometry and that of phytic acid by gradient elution ion exchange chromatography. Statistical analyses were done with SPSS 10.0. Results Absorption of β-carotene, ascorbic acid, riboflavin, and thiamine was 63% to 75.6%. There was a negative non-significant trend in values of β-carotene absorption with increased intake of β-carotene ( r = − 0.51, P > 0.1) and iron ( r = −0.67, P = 0.1) but a positive significant trend with riboflavin intakes ( r = 0.84, P = 0.018). Percentage of absorption of ascorbic acid showed weak positive associations with intakes of riboflavin ( r = 0.71) and ascorbic acid ( r = 0.5). Percentage of absorption of ascorbic acid was positively correlated with percentage of absorption of β-carotene ( r = 0.80, P < 0.05), iron, and riboflavin ( r = 0.64, P = 0.086), indicating some common influencing factors. Percentages of absorption for zinc (20.2), iron (9.9), and copper (17.6) was comparable with those reported for soy protein-based, high phytate diets. Pattern of phytic acid in the meals and output indicated partial degradation and absorption (34%). Conclusions For vegetarian Indian meals, apparent absorptions of β-carotene and ascorbic acid were 76% and 73.5% and of riboflavin and thiamine was 63%. Zinc, copper, and iron showed a lower absorption (10% to 20%).

Development of a laboratory baking test for Uruguayan French style hearth bread using Canadian wheat flour

Straight grade Canadian wheat (Triticum aestivum L.) flours milled from a high and medium protein Canada Western Red Spring (CWRS) wheat, a commercial sample of Canada Prairie Spring Red (CPSR) wheat and a recently released CPSR variety, 5700PR, were used to develop and assess the impact of absorption, fermentation time and flour type on a laboratory-scale Uruguayan French style hearth bread baking procedure. The lean formula dough, containing flour, yeast, ascorbic acid, malt, yeast food and optimum water absorption as determined by dough feel, was mixed to peak development in a GRL 1000 mixer, fermented, and divided into multiple (175-g) pieces. Dough pieces were sheeted and moulded using a commercial hearth bread moulder, proofed, cut (diagonal top surface cut) and baked in a modified National laboratory oven equipped with steam. Optimum dough absorption for all four flours was 62% in spite of a wide range in farinograph absorption. Optimum fermentation time was 75 min based on moulded dough length, bread volume and form, cut width and crumb texture and colour. The lower protein CWRS and the CPSR variety, PR5700, showed superior overall performance relative to the other wheat flours. The performance of the commercial CPSR flour was clearly inferior to all other wheat flours. Excellent reproducibility was obtained for all measured parameters allowing good discrimination among samples. This baking procedure should prove useful in assessing the performance of Canadian wheat classes and varieties for Uruguay and other South American markets where similar bread is popular. Key words: Triticum aestivum L., wheat, baking, hearth bread, Uruguayan bread, Canadian wheat, Canada Western Red Spring, Canada Prairie Spring Red

Ascorbic Acid as a Free Radical Scavenger in Porcine and Bovine Aqueous Humour

Aim: To study the antioxidant activity, UV absorption, concentration and stability of ascorbic acid (AA) in porcine and bovine aqueous humour (AH). Methods: Porcine and bovine AH was taken within 5 min after death and frozen at –70°C. The characteristic UV absorption band of AA and the concentration of AA in AH was determined by UV spectrophotometry. The antioxidant activity of AA to serve as a free radical scavenger in AH has been determined by using a novel fluorescent probe for antioxidants, the azoalkane 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO). The fluorescence lifetime and intensity of this probe reflect the concentration of dissolved antioxidants. The time-resolved fluorescence of DBO (laser excitation at 351 nm) in AH and in a neutral phosphate-buffered saline (PBS) solution containing only the natural amount of AA as an additive were measured. Results: The characteristic UV absorption band of AA has its maximum at 266 nm in AH. The concentration of AA in porcine and bovine AH was found to be 0.547 ± 0.044 and 1.09 ± 0.16 mM, respectively, by spectrophotometry. The fluorescence lifetime of the probe DBO was reduced from 320 ± 5 ns in pure aerated PBS to 205 ± 5 ns in porcine AH and 165 ± 3 ns in bovine AH. A detailed kinetic analysis of the lifetime shortening suggests that AA contributes approximately 75 and 85% to the antioxidant activity of porcine and bovine AH, respectively. Conclusions: Our experiments suggest that AA is the major contributor to the antioxidant activity of porcine and bovine AH. The role of AA to serve as an antioxidant in AH is discussed. In addition, UV spectrophotometry is established as an alternative method to determine the concentration of AA in AH.

Iontophoresis promotes percutaneous absorption of l-ascorbic acid in rat skin

Background: Percutaneous absorption of ascorbic acid is limited by its impermeability and instability. Objective: We attempted to improve the percutaneous absorption of ascorbic acid by use of iontophoresis after topical application of ascorbic acid. Methods: Radioactivities extracted from epidermal, dermal and blood compartments after topical application of [ 14C]ascorbic acid was measured in the presence or absence of iontophoresis. Autoradiography was also performed to study the histological distribution of the radioactivity of ascorbic acid. Results: Iontophoresis greatly enhanced percutaneous absorption of [ 14C]ascorbic acid in the rat skin. Radioactive ascorbic acid in the dermis reached a maximum level at 1 h after application whereas, in the topical application method, the uptake of ascorbic acid in both epidermis and dermis was quite low. Autoradiography of skin specimens indicated that iontophoresis accelerated the absorption of ascorbic acid through both transepidermal and pilo-sebaceous routes. Conclusion: Iontophoretic delivery system of ascorbic acid may provide a more efficient tool for its percutaneous absorption than a simple topical application.

Flavonoid Inhibition of Sodium-dependent Vitamin C Transporter 1 (SVCT1) and Glucose Transporter Isoform 2 (GLUT2), Intestinal Transporters for Vitamin C and Glucose

Vitamin C and flavonoids, polyphenols with uncertain function, are abundant in fruits and vegetables. We postulated that flavonoids have a novel regulatory action of delaying or inhibiting absorption of vitamin C and glucose, which are structurally similar. From six structural classes of flavonoids, at least 12 compounds were chosen for studies. We investigated the effects of selected flavonoids on the intestinal vitamin C transporter SVCT1(h) by transfecting and overexpressing SVCT1(h) in Chinese hamster ovary cells. Flavonoids reversibly inhibited vitamin C transport in transfected cells with IC(50) values of 10-50 microm, concentrations expected to have physiologic consequences. The most potent inhibitor class was flavonols, of which quercetin is most abundant in foods. Because Chinese hamster ovary cells have endogenous vitamin C transport, we expressed SVCT1(h) in Xenopus laevis oocytes to study the mechanism of transport inhibition. Quercetin was a reversible and non-competitive inhibitor of ascorbate transport; K(i) 17.8 microm. Quercetin was a potent non-competitive inhibitor of GLUT2 expressed in Xenopus oocytes; K(i) 22.8 microm. When diabetic rats were administered glucose with quercetin, hyperglycemia was significantly decreased compared with administration of glucose alone. Quercetin also significantly decreased ascorbate absorption in normal rats given ascorbate plus quercetin compared with rats given ascorbate alone. Quercetin was a specific transport inhibitor, because it did not inhibit intestinal sugar transporters GLUT5 and SGLT1 that were injected and expressed in Xenopus oocytes. Quercetin inhibited but was not transported by SVCT1(h). Considered together, these data show that flavonoids modulate vitamin C and glucose transport by their respective intestinal transporters and suggest a new function for flavonoids.

Pharmacokinetic model of ascorbic acid in healthy male volunteers during depletion and repletion.

To develop a new pharmacokinetic model for ascorbic acid (vitamin C) since no previously published model describes ascorbic acid absorption and disposition over a broad physiologic range of doses and plasma concentrations. A new model was developed through exploratory simulations. The model was fitted to pharmacokinetic data obtained from seven healthy volunteers who underwent ascorbic acid depletion then gradual repletion. Concentrations of ascorbic acid were measured in plasma and urine. Final pharmacokinetic model parameter estimates were obtained using nonlinear regression analysis. The new model included saturable absorption, distribution and renal tubular reabsorption parameters. The model described ascorbic acid concentrations in plasma, cells, and urine during depletion and gradual repletion phases with a residual error less than 15%. The model was useful for obtaining a new understanding of the likely causes for the complex concentration-time profile observed during gradual repletion. At doses of 200 to 2500 mg per day, the plateau in pre-dose concentrations is largely due to apparent saturation of tissue uptake and less a function of oral bioavailability and renal excretion than previously thought.

Hydrolysis and absorption of two monophosphate derivatives of ascorbic acid by channel catfish Ictalurus punctatus intestine

Brush-border membrane vesicles prepared from channel catfish intestine released phosphate from two monophosphate-stabilized forms of ascorbic acid (AA) at comparable rates, with activity in proximal intestine exceeding that in distal intestine. Apical absorption of AA by everted intestinal sleeves was greater in proximal intestine with maximal rates of absorption for the phosphate-stabilized forms comparable, but about 40% of those for native AA. Rates of passive influx were negligible for all forms of AA. Although the presence of phosphate groups delayed absorption, presumably because the phosphate had to be removed before AA translocation, affinity of carriers was higher for the monophosphate than native AA. This suggests less of the monophosphate AA is oxidized prior to uptake allowing a greater percentage to be transported via the high affinity, Na +-dependent transporter. These findings imply bioavailability of the two monophosphate-stabilized forms of AA is dependent on a two-stage process: (1) intestinal hydrolases remove the phosphate group then (2) absorption of released AA via carrier-mediated processes that are comparable to those of mammals. Capacities of catfish intestine to release and absorb AA from both phosphate-stabilized forms exceed estimates of daily requirements by at least three orders of magnitude.

Comparison of Absorption of Erythorbic Acid and Ascorbic Acid in Guinea Pig Small Intestine.

Both the ascorbic acid (AsA) and erythorbic acid (ErA) absorption in the small intestine of guinea pigs were determined by the perfusion of the small intestine using isotonic phosphate buffer recycled in situ. The absorption rate of AsA in the small intestine of guinea pigs was higher than that of ErA; however, Km of AsA absorption was lower than that of ErA in normal guinea pigs. In AsA-deficient guinea pigs, the absorption rates of both AsA and ErA were higher than those in normal ones. The absorption of AsA and ErA in the small intestine of guinea pigs was inhibited by ouabain. Furthermore, AsA and ErA inhibited each other's absorption. Based on the results, the net amount of the absorbed ErA in the small intestine may be lower than that of AsA, and ErA absorption mechanism seemed to be similar to that of AsA. The absorption rate of both AsA and ErA in the small intestine of guinea pig might be dependent on the AsA level in the tissues.

Absorption of ascorbic acid and ascorbic sulfate and ascorbate metabolism in common carp (Cyprinus carpio L.)

Ascorbate metabolism was analyzed in fasted common carp and carp offered diets lacking ascorbic acid or supplemented with ascorbic acid (AA) or ascorbic sulfate (AS). Ascorbic acid and ascorbic sulfate were analyzed in the contents collected from various parts of the digestive tract. The major site of the dietary ascorbate absorption was located in the first 20% of the anterior intestine region (58.7 +/- 10.2%), whereas absorption increased to 94.3 +/- 1.9% (in the whole gut). Considerable secretion of ascorbate into the initial part of the intestine was found (71 micrograms AA.g-1 dry food) in fish offered the diet lacking ascorbate, but this amount was completely reabsorbed in the following portions of the intestine. AS was concentrated in the contents of the digestive tract and the external marker method revealed no absorption of AS from the intestine. In fish fed the AA-supplemented diet, the concentration of ascorbate in plasma, hepatopancreas, kidney, intestine, spleen, and brain was significantly (P less than 0.01) higher than in similar tissues from the other groups, suggesting that ascorbic sulfate hydrolysis was ineffective. Small amounts of AS were found in the intestine and spleen of fish fed a diet supplemented with AS. Ascorbate analysis in the whole fish allowed the estimate of the catabolic rate of fasting and scorbutic-diet-fed fish, which amounted to 0.7% and 1.46% daily of the ascorbate body pool, respectively. There was no indication that ascorbic sulfate sulfohydrolase activity was induced in hepatic, kidney, or intestinal tissue of fish offered a diet with AS in comparison to other groups. It seems unlikely that cyprinid fish are able to utilize ascorbic sulfate as a vitamin C source, and thus resemble scurvy-prone mammals in this respect.

Intestinal absorption and metabolism of ascorbic acid in rainbow trout

Transport and metabolism of the reduced and oxidized forms of vitamin C were evaluated in trout intestine in vitro. Transepithelial fluxes of [14C]ascorbic acid were determined with the substrate present at 10 microM. The mucosa-to-serosa flux was fourfold greater than the serosa-to-mucosa flux with ascorbic acid present in both bathing solutions. Cellular accumulation of the reduced molecule occurred with a final tissue-to-medium ratio of 1.64. Ascorbic acid influx across the brush-border membrane was determined under conditions that inhibit transport of other nutrients. Influx was not reduced because of the presence of the D- or L-stereoisomeric form of glucose but was highly dependent on the presence of Na in the bathing medium. Brush-border influx was saturable with a Km of 220 microM. Short-term (8 min) exposure of intestinal loops to the oxidized form of vitamin C, dehydro-L-ascorbic acid, was followed by high-performance liquid chromatography analysis of the 14C label present in the tissue. Total uptake of substrate was greater from the serosal solution than from the mucosal solution; in either situation most of the 14C label was found in the reduced state. It is concluded that transport and metabolic capabilities are present in the trout intestine to absorb oxidized and reduced forms of vitamin C and to help regulate the redox potential of circulating ascorbic acid by recycling dehydro-L-ascorbic acid.

Absorption of Ascorbic Acid and Ascorbic Sulfate and their Interaction with Minerals in the Digestive Tract of Rainbow Trout (Oncorhynchus mykiss)

The sites of absorption of ascorbic acid (AA) in the rainbow trout (Oncorhynchus mykiss) gut were located in the stomach (20.7%), pyloric caecae region (23.4%), middle intestine (21.9%) and posterior intestine (20.1%). Ascorbic sulfate (AS) were found to be absorbed in the stomach (27.7%) although it is likely that the figure obtained is an overestimate. This conclusion is based on the concentration factor of the intestinal contents (faeces/food ratio) being much higher for ascorbic sulfate than for an external dietary marker, chromic oxide. The apparent protein absorption rates from the three diets used were not significantly different (P &lt; 0.01), ranging from 86.9 to 91.5%. Three subsequent samplings, one week apart, did not reveal changes in AA or AS absorption in trout, suggesting that fish were neither "saturated" with AA nor had they developed the means to utilize the dietary AS. In most cases, the mineral contents in faeces were similar for all diets, although the concentration factors (faeces/food level), varied greatly during the course of the trial (1.9–7.1 for Zn, 1.8–4.9 for Fe, and 2.4–3.7 for Cu). The concentrations of Fe and Zn in the contents of the posterior intestine were lower in the fish fed an AA-supplemented diet than in fish fed on AS and deficient diets, which may suggest an increased absorption of these elements.

Oral administration of different formulations of ascorbic acid to the horse

Summary The absorption of crystalline ascorbic acid, ascorbyl palmitate, ascorbyl stearate and a formulation of ascorbic acid was investigated in six mature Thoroughbred horses following oral administration. It was found that ascorbyl palmitate gave both highest plasma concentrations and greatest area under the curve (AUC) for ascorbic acid. Least variation between animals also occured for this preparation. No apparent absorption was seen in some animals given ascorbic acid or ascorbyl stearate.

Ultraviolet absorption substances in cerebrospinal fluid of normal pressure hydrocephalus

Optical densities (OD) were measured in ultraviolet absorption ranging from 210 to 310 nm in cerebrospinal fluid (CSF) samples obtained from 33 cases of adult normal pressure hydrocephalus. CSF samples from 100 patients, who had no neurological disorders served as control. All cases of adult normal pressure hydrocephalus were divided into three groups (excellent, good, non effective) according to the clinical improvement following the ventriculo-peritoneal (V-P) shunt operation. Two absorption peaks were ordinarily found in spectrophotometric analysis in CSF. The first peak at 230 nm was identified as the complex of albumin, γ-globulin and a few peptides through various biochemical analyses. The OD at 230 nm were significantly higher in both the excellent and good groups than in the normal control group (P<0.02, P<0.05) . For 24 hours prior to the shunt operation, continuous CSF drainage was made through lumbar route and the samples taken after 24 hours showed marked increases in the OD at 230 nm in the excellent and the good recovery groups. The second peak at 267 nm known as ascorbic acid absorption, remained significantly lower in all three groups than in the control group (P<0.001). Meglumine iothalamate (MI) was found in CSF as the maximum absorption at 245 nm following intravenous administration. Twenty-two samples taken 24 hours after intravenous administration of 100 ml of MI were studied. The OD at 245 nm were significantly higher in the excellent recovery group than the one in the non effective group (P<0.01). The increases in OD at 230 and 245 nm were thought to be due to the impairment of either the blood-brain or blood-CSF barrier and the development of edema in brain parenchyme. The cases who had high OD at 230 nm responded well to the V-P shunt operation. This was probably due to the removal of edema fluid through the hydrostatic pressure gradient between the brain and the ventricle. These results may be useful in deciding on surgical indication on patients of normal pressure hydrocephalus.

Impairment of absorption of ascorbic acid following ingestion of aspirin in guinea pigs

A study was undertaken to investigate the interactions between aspirin and ascorbic acid in guinea pigs. Animals received by gastric intubation either a single dose of radiolabelled ascorbic acid alone or ascorbic acid with aspirin and the exhalation of CO 2 was monitored for 400 min following administration. Animals receiving the vitamin only reached plasma peak levels within 90 min following administration while coadministration of the vitamin with aspirin, not only resulted in lower plasma peak levels, but also delayed their attainment until after 160 min. The bioavailability of ascorbic acid during the first 400 min was reduced by half following simultaneous administration of aspirin. The initial rate of exhalation of CO 2 was decreased by 70% following coadministration of aspirin. These observations indicate that aspirin impairs the gastrointestinal absorption of ascorbic acid in guinea pigs, possibly by interfering with its active transport.

Ascorbic Acid Absorption in Humans: A Comparison among Several Dosage Forms

There have been few studies conducted to determine the efficiency of ascorbic acid absorption in humans. Differences in the extent of its absorption among individuals may contribute to the outcome of clinical trials. Ascorbic acid absorption in four subjects was investigated from several oral dosage forms containing 1 g of the vitamin (solution, tablet, chewable tablet, and timed-release capsule). Approximately 85% of an intravenous dose was recovered in the urine as ascorbic acid and its major metabolites. In contrast, only ~30% of the dose was recovered from the solution and tablet forms. A considerably smaller fraction of the dose (~14%) was recovered from the timed-release capsule. There was considerable intersubject variation in ascorbic acid absorption and there appeared to be good and poor absorbers of the vitamin. Consideration should be given to the influence of the extent of ascorbic acid absorption on the results of clinical trials.