Ascorbic acid absorption in man: influence of divided dose and food

Effect of Aloe vera preparations on the human bioavailability of vitamins C and E

There are no literature references describing the effect of consumption of Aloe vera liquid preparations on the absorption of water- or fat-soluble vitamins. There is a very large population worldwide which consume vitamins and many people also consume Aloe. Thus we report the effect of Aloe on the human absorption of vitamins C and E, the most popular vitamin supplements. The plasma bioavailability of vitamins C and E were determined in normal fasting subjects, with eight subjects for vitamin C and ten subjects for vitamin E. In a random crossover design, the subjects consumed either 500 mg of ascorbic acid or 420 mg of vitamin E acetate alone (control), or combined with 2 oz of two different Aloe preparations (a whole leaf extract, or an inner fillet gel). Blood was collected periodically up to 24 h after consumption. Plasma was analyzed for ascorbate and tocopherol by-HPLC with UV detection. There was no significant difference in the areas under the plasma ascorbate-time curves among the groups sincerely due to large differences within the groups. For comparative purposes the control area was 100%. The Aloe Gel area was 304%, and Aloe Whole Leaf 80%. Only Aloe Gel caused a significant increase in plasma ascorbate after 8 and 24 h. For vitamin E, the results for the relative areas were control 100%, Gel 369%, and Leaf (198%). Only the Aloes produced a significant increase in plasma tocopherol after 6 and 8 h. Both Aloes were significantly different from the control after 8 h. Aloe Gel was significantly different from the baseline after 24 h. The Aloes slowed down the absorption of both vitamins with maximum concentrations 2-4 h later than the control. There was no difference between the two types of Aloe. The results indicate that the Aloes improve the absorption of both vitamins C and E. The absorption is slower and the vitamins last longer in the plasma with the Aloes. Aloe is the only known supplement to increase the absorption of both of these vitamins and should be considered as a complement to them.

Intestinal absorption in health and disease: micronutrients

The main theme of this chapter concerns the precise biochemical mechanisms involved in stages up to, and including, gastrointestinal absorption of vitamins and certain selected minerals. Essential data regarding sequential events, immediately following absorption of these micronutrients, are also included. There is reference to water-soluble vitamins that are, in general, either coenzymes in various metabolic reactions or carriers of certain biochemical groupings. In contrast, fat-soluble vitamins frequently function as integral components of cell membranes; they, too, receive ample attention. It is appropriate, nevertheless, to recognize that some minerals required in very small amounts are closely allied biochemically with particular vitamins; these specific associations are apportioned emphasis at relevant places in the text. Although predominant discussion centres on the physiological state, clinical reference is necessarily made to gastrointestinal disorders in which imbalance of vitamins and minerals consequently results in an additional detrimental impact on health.

In vitro gastrointestinal digestion study of pomegranate juice phenolic compounds, anthocyanins, and vitamin C

Pomegranate is an important source of bioactive compounds, such as anthocyanins, other phenolic compounds, and ascorbic acid. In the present work an in vitro availability method has been used to assay the influence of the physiological conditions in the stomach and small intestine. This method enables the study of the release of anthocyanins, vitamin C, and total phenols from the pomegranate juice and their transformations during gastrointestinal digestion. Results have shown that pomegranate phenolic compounds are available during the digestion in a quite high amount (29%). Nevertheless, due to pH, anthocyanins are largely transformed into non-red forms and/or degraded (97%), and similar results are obtained for vitamin C (>95% degradation).

Correlation between the disintegration time and the bioavailability of vitamin C tablets

The goal of this study was to examine if the current USP disintegration standard for vitamin C tablets (max. 30 min in water at 37 degrees C with disks) is adequate or if a tighter disintegration standard (e.g., European compendia max. 15 min) should be recommended based on bioavailability considerations. Four formulations of 500-mg vitamin C tablets ranging in mean disintegration time from 9 to 120 min were compared with a standard vitamin C solution in a double-blind clinical trial with 15 subjects. The products were administered with a standard breakfast. The data show that a solution of vitamin C and a fast-disintegrating tablet (8-9 min) have equal but significantly lower bioavailability than tablets with longer disintegration times (30, 60, 120 min). Tablets with a mean disintegration time of 60 min showed the highest bioavailability. When the disintegration test was performed without disks, disintegration times increased so much that only the tablets with the fastest disintegration time (which were also the tablets with the lowest bioavailability) met the current USP disintegration time limit. Based on the results of the study, changes in the USP standard to omit the disks or to shorten the disintegration time will not achieve enhanced bioavailability but will result in reduced vitamin C absorption. In vitro dissolution of vitamin C tablets did not show the traditional relationship with bioavailability.

Changes in plasma and buffy layer vitamin C following surgery

Postoperative changes in plasma and buffy layer (BL) vitamin C were studied in 107 patients receiving either 0 (37 patients), 100 mg (33 patients) or 500 mg (37 patients) vitamin C supplements daily. In patients receiving no supplement plasma vitamin C concentrations had fallen (mean 33 per cent) by the first postoperative day and thereafter changed little. The falls occurred irrespective of initial plasma concentration, were greater the higher the initial concentration, but tended to be proportional to the length of operation. In patients given supplements this loss of vitamin C was evident but modified, and from the second postoperative day the response to the supplements was as would have been expected in non-operated subjects. The most probable explanation for the loss of vitamin C from plasma was an increased urinary excretion during operation. Changes in BL vitamin C concentrations were studied in relation to changes in leucocyte and platelet counts. The previously reported postoperative falls in BL vitamin C were found to be the result of a major artefact in the methods routinely used for BL vitamin C estimation, caused by changes in the leucocyte and platelet populations, most importantly the platelet to leucocyte ratio. No true demand for vitamin C, as measured from the buffy layer cells, was evident.

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 approximately 30% of the dose was recovered from the solution and tablet forms. A considerably smaller fraction of the dose (approximately 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 trails.