Vitamin comparative bioavailability

In the only known human study of vitamin D bioavailability from natural sources (43), the average relative bioavailability of vitamin D2 from meat sources was estimated to be about 60% as compared to a vitamin supplement. 

Gum formulations containing caffeine showed rapid release and absorption of the agent with comparable bioavailability to the capsule form [57], Various gum formulations with vitamin C [56], diphenhydramine [58], methadone [59], and verapamil [60] have been developed and tested. 

N3. Nelson, E. W., Streiff, R. R., and Cerda, J. J., Comparative bioavailability of folate and vitamin C from a synthetic and natural source. Am. /. Clin. Nutr. 28,1014-1019 (1975). Nicol, D. J., and Davis, R. E., The folate and vitamin B12 content of infant milk foods with particular reference to goat s milk. Med. J. Aust. 2, 212-213 (1967). 

In order to exhibit provitamin A activity, the carotenoid molecule must have at least one unsubstituted p-ionone ring and the correct number and position of methyl groups in the polyene chain. Compared to aU-trans P-carotene (100% provitamin A activity), a-carotene, P-cryptoxanthin, and y-carotene show 30 to 50% activity and cis isomers of P-carotene less than 10%. Vitamin A equivalence values of carotenoids from foods have been recently revised to higher ratio numbers (see Table 3.2.2) due to poorer bioavailability of provitamin A carotenoids from foods than previously thought when assessed with more recent and appropriate methods. 

Most of fhe above-mentioned bioavailability, intervention, and case studies came to the conclusion that water-miscible or water-soluble preparations of faf-soluble vitamins were superior to regular supplements. Based on the evidence from our own bioavailability study as well as from fhe studies mentioned above, it therefore seems justified to assume that fat-soluble vitamin deficit patients with fat maldigestion and/or malabsorption can be corrected more efficiently by using water-soluble as opposed to fat-soluble preparations. Another advantage of water-soluble preparations in general might be that lower daily doses are required when compared to fat-soluble preparations to achieve the same results. 

Methylcobalamin is the coenzyme form of vitamin It is neurologically active, most bioavailable and best utilized. Unlike cyanocobalamin, it does not require any conversion after absorption by the body and is better retained by the liver and other tissues. It has exhibited beneficial effects against brain aging, irregular sleep patterns. It supports immune function and promote normal cell growth. It represents one of the best values in nutritional products, given its comparably low cost and its wide range of potential benefits. 

Citrus juice is rich in ascorbic acid and, therefore, is an important dietary source of this essential vitamin. Our studies were aimed at defining whether vitamin C from citrus sources is comparable with the synthetic vitamin in terms of bioavailability and intestinal absorption. These studies were conducted using human volunteers and guinea pig experimental models (1, 2). 

The bioavailability of vitamin E from a self-emulsifying preparation was evaluated in comparison to a commercially available soybean oil solution in soft gelatin capsule. Vitamin E administered as a self-emulsifying preparation had markedly higher plasma levels compared to the oil solution formulation, and the extent of absorption was increased almost threefold. Moreover, variability between subjects was markedly reduced in the case of the self-emulsifying preparations [32],... 

In many cases the relatively complex nature of lipid-based formulations in terms of lipid class, chain length, degree of dispersion, and choice of surfactant makes explanation of the mechanistic information difficult. For example, the bioavailability of vitamin E after administration of vitamin E acetate is greater after administration in a medium-chain triglyceride (MCT)-based emulsion compared with a long-chain triglyceride (LCT)-based lipid solution however, the differential roles of lipid dispersion or lipid class (MCT vs. LCT) cannot be separated [37],... 

Emulsions have been used for centuries for the oral administration of medical oils and vitamins and as dermatological vehicles. Recently, their application has been extended as drug carriers in the delivery and targeting of ophthalmic drags. An indomethacin emulsion has been reported to increase ocular bioavailability and efficacy compared to commercially available formulation in rabbits. 0.4% indomethacin emulsion showed 2.2 fold increase in the area under the anterior aqueous drag concentration/time curve compared to a 1% indomethacin suspension. The emulsion formulation also reduced ocular surface irritation caused by indomethacin Similar advantages have been shown for a pilocarpine emulsion which produced a prolonged therapeutic effect in comparison with pilocarpine hydrochloride eyedrops in man. It can be administered only twice a day, rather than four times daily for conventional formulation. 

Dietary vitamin E requirements frequently are expressed as milligram a-tocopherol equivalents, but food and supplement labels typically use lU to express vitamin E activity, and 1.0 lU is equivalent to l.Omg of all-racemic-a-tocopherol acetate. The relative activity of all racemic-a-tocopherol is set at 74% that of RRR-a-tocopherol, considered to have the highest bioavailability, and thus as the standard against which all the others mnst be compared. ... 

Many active principles of interest in cosmetics were complexed with cyclodextrins. achieving positive and interesting results. For instance, the inclusion of retinol in hydroxypropyl-P-cyclodextrin leads to a water-soluble product, sufficiently stable, of higher bioavailability and lower toxicity compared to free retinol. Similarly, it is possible to include almost all vitamins in cyclodextrins. with unquestionable advantages with regard to their... 

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