ProView - The technical publication for Infinity2 health professionals. Volume 6 • Number 1
Cellular Nutrition By: J. Ferniza, MS, CCN, CSCS Introduction
Millions of people take supplements each day, but few people know what is actually in the supplement they’re taking. And even fewer know whether or not the supplement is truly nourishing the cells of the body. True nutrition is ‘cellular nutrition’ and was defined by Dr. Stan Bynum as ‘to nourish the cells of the body in order to optimize metabolism’. In order for cellular nutrition to occur, the nutrients in foods and supplements must reach the cells of the body and they must be supplied in a form that the body can use with all of the necessary cofactors included.
A formulator can put as much "nutrition" as he wants in a product, but it makes no impact on the body unless it gets to the cells. Nourishing the cells requires a careful balance of nutrients and their actions. Cellular nutrition is based not on a list of recommended amounts, but on what is actually delivered to and usable by the cells of the body. This is what is referred to as bioavailability, or available to and usable by the cells. Ensuring that the supplements you take are bioavailable is paramount to cellular nutrition.
Achieving Cellular Nutrition
In order to achieve cellular nutrition several steps must be followed, as determined by nature. The previous issue of ProView explained the role of digestion and a healthy gastrointestinal tract in the seven steps of nutrition. This issue will focus on the mechanisms of absorption, transport and assimilation of the micronutrients (vitamins and minerals) in achieving cellular nutrition, as well as the importance of the source and form of the nutrient in bioavailability.
Absorption is often confused with bioavailability. Bioavailability is a measure of how well the body can utilize the nutrient. It is a function of both the form of the nutrient and the body’s need for it. Absorption is a measure of how well the nutrient is transferred from the GI tract into the blood or lymph system. There are many substances that are absorbed; but, for a number of reasons, are not utilized by the body.
Although absorption is not equivalent to bioavailability, it is a key component in bioavailability and the seven steps of nutrition. For absorption to occur, the nutrients must be transported across the cell membrane into the mucosal cell and then out of the mucosal cell and into the circulation (31). Absorption requires one of four categories of membrane transport mechanisms (illustrated in Figure 1, pg.2): Passive diffusion, facilitated diffusion, active transport, and pinocytosis (31). Facilitated diffusion and active transport are unique in that they utilize membrane transport proteins that are specific to individual nutrients (6;31;35-37).
Each nutrient can use one or more of these mechanisms to be transported across the cell membrane. At physiological doses (low doses), active transport and facilitated diffusion are the primary absorption mechanisms for minerals and water soluble vitamins, with passive diffusion playing a role at higher doses (31). Fat soluble vitamins are incorporated into micelles in the lumen and transported into the mucosal cell via passive diffusion (31).
Once inside the mucosal cell, the nutrients must be converted to a form that can be used by the body and can be transported to the liver and other tissues. Minerals are chelated (bound) to an amino acid or specific carrier protein in the mucosal cell (6;42). Most water-soluble vitamins (particularly the B vitamins) are phosphorylated within the mucosal cell and many are eventually bound to a specific transport protein(31). The minerals and water-soluble vitamins are then transported to the liver via the portal vein. After leaving the liver, most vitamins and minerals are transported through the blood bound to various specific and non-specific proteins, such as albumin(28;31;42). Assimilation of these nutrients into the cells of the body occurs primarily by active transport into the cell and, like absorption, the transport proteins are usually specific to the nutrient(2).
After entering the mucosal cell via micelles, fat soluble vitamins are incorporated into chylomicrons and enter the lymphatic system, which eventually "dumps" back into general circulation (2). The chylomicrons are hydrolyzed in the circulation by the enzyme lipoprotein lipase, which releases some of the fat soluble vitamins to be assimilated and used by the cells of the body. The rest remain as part of the chylomicron remnant and are taken up by the liver, where they can be stored or reincorporated into lipoproteins to be re-released into circulation as part of VLDL and LDL (2).
How effectively these processes occur will help determine whether cellular nutrition is achieved. Because these processes are enzyme dependent, the form of the nutrient and the availability of its cofactors play a key role in bioavailability and cellular nutrition. This is where the quality of a nutritional supplement is evaluated. Does the supplement provide nutrients in a form that can be absorbed and used by the body? Does the supplement provide all of the necessary cofactors?
Vitamins
Are the vitamin supplements you use providing complete nutrition or only a fragment of true nutrition? The answer can be found in the ingredients of the supplement and in the answers to the next two questions. ‘Is ascorbic acid truly vitamin C?’
‘Is alpha-tocopherol really vitamin E?’
The truth is ascorbic acid is only a part of vitamin C and alpha-tocopherol is only a part of vitamin E. Therefore, if ascorbic acid and alpha-tocopherol are listed on the label as vitamin C and Vitamin E, then you are only getting a fragment of true nutrition.
Vitamins, as found in nature, are groups of chemically related compounds. There is a part of this complex that science identifies as the "organic nutrient." In the case of vitamin C, this organic nutrient is ascorbic acid. In the case of vitamin E, it is alpha-tocopherol. Many people think that if you supply the body with these simplified "organic nutrients" in the amounts specified by the RDA, you provide all the ‘nutrition’ required for health.
The problem with this idea is it does not take into consideration all of the enzymes, precursors, co-enzymes, antioxidants, trace elements, activators and numerous other naturally occurring synergistic micronutrients that we may or may not at this time know about. These other elements are required for the organic nutrient to be used by the body. For example, alpha-tocopherol is only one part of the vitamin E complex. A complete, natural vitamin E not only contains alpha-tocopherol, but also provides gamma-tocopherol, and the other tocopherols and tocotrienols.
These other components of vitamin E are as important as alpha-tocopherol and these components work together synergistically to create all of the observed health promoting effects of vitamin E. Yet, only alpha-tocopherol is given an RDA and is what is listed on supplement labels.
Have you ever wondered why the alpha-tocopherol supplementation studies have failed to demonstrate a positive effect for heart disease (3;25;26), when other studies have demonstrated clearly that there is a strong correlation between low plasma vitamin E levels and the incidence of coronary heart disease (20)? A closer look at the results of these studies provides some insight.
First, the supplements used in these studies are not natural vitamin E. They consist primarily (or solely) of alpha-tocopherol, whereas dietary sources of vitamin E provide a balance of all the tocopherols and tocotrienols. In support of this, one of these studies, published in the New England Journal of Medicine (26), actually stated that vitamin E appeared to offer protection only when taken up from the diet.
Second, alpha-tocopherol is not the only indicator of vitamin E status. A recent clinical evaluation of individuals with coronary heart disease showed decreased serum levels of gamma-tocopherol, but not alpha-tocopherol (32). Could it be that gamma-tocopherol is as important as alpha-tocopherol in preventing disease and promoting health?
Gamma-tocopherol is important and actually complements alpha-tocopherol in its activities (16). Gamma-tocopherol is able to get rid of peroxynitrite, a highly destructive nitric-oxide radical found at sites of inflammation (16). It also appears to be the only component of vitamin E that can permanently trap and remove nitrogen oxide, a chemical commonly found in polluted air (16).
And don’t forget the tocotrienols! Recent research has shown that not only are tocotrienols more potent antioxidants than alpha-tocopherol, but they also have the ability to reduce cholesterol, reduce the atherogenic apolipoprotein B and lipoprotein (a), and possess anti-thrombic and anti-tumor properties (38).
It appears that alpha-tocopherol is NOT the same as a complete, natural vitamin E, nor is it as bioavailable as natural vitamin E. Not only does natural vitamin E provide a complete vitamin, but there is a difference in the chemical structure of natural vitamin E that makes it more absorbable and bioavailable than synthetic vitamin E, even when comparing only one fraction of the vitamin. Enough research has been done comparing natural alpha-tocopherol (RRR) to synthetic (all-rac), that there is an accepted conversion factor of 1.36, meaning that natural alpha-tocopherol is 1.36 times more bioavailable than synthetic alpha-tocopherol (15;18;39). Still others propose that the natural form is more than twice as bioavailable as synthetic forms (14;24), as indicated in a proposal to the Food and Nutrition Board of the National Academy of Sciences, USA to change the biopotency factor from 1.36 to 2.
Together these results suggest a critical role for the natural vitamin with all of its components in the prevention of cardiovascular diseases. Supplements containing only alpha-tocopherol are not only less effective, but may create nutrient imbalances. Research has shown that alpha-tocopherol supplementation actually suppresses gamma-tocopherol levels (22).
The same principles of bioavailability and supplying a complete nutrient apply to the other vitamins as well. Studies comparing natural versus synthetic sources of beta-carotene and vitamin C have shown that the natural sources are absorbed better, are more bioavailable, and have greater functional activity than synthetic (11;40;41). The Nutrition Desk Reference states, "natural vitamin C that contains bioflavonoids may have advantages over the synthetic form of vitamin C… bioflavonoids have been shown to improve the utilization and storage of vitamin C." (19)
Just as the studies examining alpha-tocopherol and heart disease reported, beta-carotene supplementation has not been effective. Three out of four intervention trials using high dose beta-carotene supplements did not show protective effects against cancer or cardiovascular disease. Rather, the high risk population (smokers and asbestos workers) in these intervention trials showed an increase in cancer and angina cases. In a published review of these studies, Paiva and Russel (33) concluded: ‘It appears that carotenoids (including beta-carotene) can promote health when taken at dietary levels, but may have adverse effects when taken in high doses by subjects who smoke or have been exposed to asbestos’.
Nature provides more than just the few vitamins that have RDAs and are listed on a supplement label. There are over 600 carotenoids from natural sources that clearly show biological actions distinct from their function as precursors of vitamin A (12). Not to mention the numerous bioflavaoids that not only enhance vitamin C absorption and bioavailability (19;40) (41), but also posses their own anti-allergic, anti-inflammatory, antiviral and antioxidant activities (17;27;30).
Some of these nutrients, such as the proanthocyanidins (OPC), actually posses properties stronger than the typical vitamins listed on the label. For example, research has shown that OPC from grape seed extract provides significantly greater protection against free radicals and free radical-induced lipid peroxidation and DNA damage than vitamins C, E and beta-carotene (10). The natural components of foods work together with the officially recognized vitamins and minerals to promote health and prevent disease (30). These plant phytochemicals cannot be ignored as part of providing complete nutrition.
In choosing a vitamin supplement, the best way to provide all the natural phytochemicals and natural components of vitamins is to choose whole-food supplements. Whole foods and whole food complexes are entire composites, not fractions of vitamins. Whole food complexes are foods with only the water and fiber removed. These vitamins are natural and familiar to the body with all of the natural cofactors present.
Maximizing Mineral Bioavailability
Simply ingesting minerals is not enough. Once ingested, minerals must be available for use in the body; otherwise, they are nothing more than waste material. The mineral form is a key factor in determining how well the body absorbs and utilizes the nutrient. One form may go into the body tissues while another form is eliminated. Only bioavailable minerals enter and enhance the body’s metabolic processes and contribute to the maintenance and production of healthy tissues.
Inorganic mineral salts (i.e. chloride, sulfate, carbonate, ascorbate) have low bioavailability because they are poorly absorbed and have poor retention. The estimated absorption rates for mineral salts range from only 5% to 40% depending on the mineral, the pH of the intestine and interaction with other nutrients in the intestinal lumen (6;31).
Minerals that are true amino acid chelates, however, are much more bioavailable. The absorption rates are three to six times greater than mineral salts and have twice the retention (7;21;23;34).
The significant differences in bioavailability are, in large part, the result of the way that each type of mineral is absorbed and metabolized. For a mineral salt to be absorbed, the mineral must solubilize or ionize in the acid pH of the stomach after ingestion (6). Because the acid environment is essential for absorption of mineral salts, antacids have the potential to interfere with the absorption of numerous minerals. This illustrates why antacids are not necessarily a good source of calcium.
Once the mineral is in its ionic form (usually divalent), if it gets close enough, it can bind to the proteins on the mucosal cell membrane. (That is if it hasn’t bound to other food components in the digestive tract, such as fiber and phytic acid first.) The mineral is then chelated to the membrane protein so that it can be transported into the mucosal cell, released intracellularly and rechelated to a smaller protein or amino acid for transport within the cell and the plasma (6).
The improved absorption of amino acid chelates compared to mineral salts is due to the way amino acid chelated minerals are absorbed. First, amino acid chelated minerals do not need to be solubilized and do not interact with other food components in the digestive tract (13). Second, the intestinal treatment of the chelate is as a peptide rather than an ion (4;5;9) and it is already in a form that can be absorbed and transported intracellularly. This allows it to potentially avoid the two-step absorption mechanism required for other mineral forms. The process of chelation with the membrane protein and the release of the ion and rechelation with an intracellular protein for transport to the basement membrane are not necessary (4;5). The result is absorption rates and retention rates that are much greater than mineral salts because the mineral is provided in a form that the body can use.
While mineral chelation may sound simple, creating a truly bioavailable nutritional chelate is no easy task. There are several factors that determine a true chelate; its bioavailability and its use in human nutrition. To be a true chelate and be bioavailable it must have an effective chelating agent, must be properly formed, must be strong yet available, and have a low molecular weight. Even when these standards are met in creating a true chelate, for it to be used in human nutrition it must be well tolerated and have a low toxicity.
Effective chelating agent
Certain chelating agents (ligands) such as vitamin C (ascorbates), citric acid (citrates), and gluconates form mineral chelates that are too weak and end up being destroyed in the stomach (4;5;8). They have no value as nutritional chelates, and in fact, are only about as bioavailable as mineral salts, mentioned earlier. Other chelating agents, such as picolinic acid and EDTA, are strong chelators but are not metabolized by the body. As a result, the complex is not utilized and is excreted in the urine (29).
Krebs Cycle chelates are a popular concept, but their usefulness is highly suspect. The chemical structures of the organic acids of the Krebs Cycle would yield chelate rings of seven members. Such structures are very unstable. The theory is nice, but the chemistry doesn’t work for nutritional purposes.
Amino acids are the most appropriate ligand to provide a practical, nutritional chelate. These chelates are similar to the chelates formed naturally by the normal absorption process for minerals (4;6). The body is very efficient at absorbing amino acids; in fact, 95% of all amino acids are absorbed (31). Chelating minerals to amino acids allows minerals to be "smuggled" in during the transport process across the intestinal wall and allow for increased absorption.
Properly Formed
Unless an amino acid chelate is properly formed and stable, it will be of minimal nutritional value. Simply mixing inorganic minerals with amino acids in a liquid or dry mixture does not fall into the category of a true amino acid chelate. Unfortunately, many of these cheaply made, so-called "chelates" have been sold to the unsuspecting public.
Special processing must be performed to create a stable (covalent) bond which results in greater bioavailability. In forming a proper mineral chelate, chelation of the mineral must take place in an aqueous environment. Also, the chelating agent (ligand) must bond to the mineral by at least two points on the ligand to form a ring with the mineral as the closing member of the ring (5). Only then is a true chelate formed.
Strong Yet Available
A nutritionally functional chelate must be strong enough to resist being destroyed in the gastrointestinal system, yet still able to allow its mineral content to be released for use inside the body (8). At present, this unique type of chelate can only be prepared in one way, and that manufacturing method is patented by Albion Laboratories (9). Therefore, unless the amino acid chelate is produced via the Albion method, it is probably of no more nutritional value than the other inorganic mineral/protein blends that have been passed off as chelates. Mineral supplements that use Albion amino acid chelates will have the patent number included on the label.
Low Molecular Weight
A nutritionally functional amino acid chelate must also have a molecular weight that is small enough (less than 800 daltons) to allow intact absorption through the intestinal wall (5;8). Any chelate weighing over 800 daltons requires that the chelate be digested in order to be absorbed, and digestion will destroy that chelate (5;9). The building of a nutritionally functional chelate is not a simple process. It is expensive and time–consuming. However, the nutritional benefits of such a mineral more than make up for the effort.
Tolerance
Some forms of minerals have been known to cause GI irritation, including diarrhea and constipation and can irritate membranes. Albion’s patented amino acid chelates have been shown to be tolerated significantly better than other forms of supplemental minerals. The following gastric tolerance study demonstrates that Albion’s iron amino acid chelate is superior to ferrous sulfate by a factor of at least two (34).
In menstruating women, Albion’s iron amino acid chelate was preferred by 61% of the women in the study over ferrous sulfate. This high tolerance was statistically significant.
Safety
Since supplements are taken on a long-term, regular basis, safety is a major consideration. In mineral nutrition, safety is usually thought of as a function of the dose. However, since different sources of the same mineral have different safety factors, the carrier’s safety should also be considered.
LD-50 studies of Albion Chelates show them to be substantially less toxic than mineral salts (1).
Multigeneration studies and acute and sub-acute pathology studies have also shown Albion chelates to be safe and have been granted GRAS status by the FDA. In fact, Albion’s patented iron (Ferrochel) was found to have a NOAEL (no observed adverse effect level) of greater than 500 mg of iron/kg bw/day. This is an astounding safety level for any iron ingredient, let alone one that has been shown to have the high level of bioavailability and effectiveness seen in the research on Ferrochel. Albion amino acid chelated minerals are the most bioavailable, best tolerated and safest form of minerals available. They provide true cellular nutrition.
Potency is Not Determined by Milligrams levels
The RDA speaks of vitamin and mineral quantities as if all forms have equal bioavailability. No wonder the public is confused. They want to know how many micrograms or milligrams of a vitamin or mineral to take without regard to the form. Few physicians, let alone the general public, understand that there is a difference between whole food and synthetic vitamins and that amino acid chelates are absorbed differently than inorganic salts.
Potency is not necessarily how high the milligram level is, rather how effectively the nutrients are paid back. Potency is determined by bioavailability, which is providing and delivering to the cells all the missing nutritional factors with as little cost to the cell as possible. It’s quality, not quantity that counts.
Quality means providing bioavailable vitamins and minerals that result in cellular nutrition. Just ingesting these nutrients is not enough. The nutrients must be readily absorbable and bioavailable; otherwise, they are nothing more than waste material. The most bioavailable form of a mineral is an Albion amino acid chelate, and the most bioavailable, complete source of vitamins is whole food complexes. If optimal nutrition is your goal, be sure that your supplements contain these bioavailable sources of nutrients.
References
1. Chelated Mineral Nutrition in Plants and Man. Charles C. Thomas Publications. 1982, 163.
2. Modern Nutrition in Health and Disease. Baltimore, Williams and Wilkins. 1994.
3. The Alpha-Tocopherol, Beta-Carotene Prevention Study Group. NEJM 330: 1029-1035, 1994.
4. Ashmead, H. D., D. J. Graff, and H. H. Ashmead. Evidence for Two Mineral Absorption Pathways. Intestinal Absorption of Metal Ions and Chelates. Springfield, Thomas. 1985.
5. Ashmead, H. D., D. J. Graff, and H. H. Ashmead. Intestinal Absorption of Metal Ions and Chelates. Springfield, Thomas. 1985.
6. Ashmead, H. D., D. J. Graff, and H. H. Ashmead. Intestinal Uptake of Free Metal Ions. Intestinal Absorption of Metal Ions and Chelates. Springfield, Thomas. 1985.
7. Ashmead, H. H. Tissue transportation of organic trace minerals. J.Appl.Nutr. 22: 42, 1970.
8. Ashmead, H. H. Chelation does not guarantee mineral absorption. J.Appl.Nutr. 1974.
9. Ashmead, H. H., Ashmead, H. D., and Graff, D. J. Amino acid chelated compositions for delivery to specific biological tissue sites. Albion International, Inc. 826,786(4,863,898), 1-65. 9- 5-1989. Clearfield, Utah. 2-6-1986. Ref Type: Patent
10. Bagchi, D., M. Bagchi, S. J. Stohs, D. K. Das, S. D. Ray, C. A. Kuszynski, S. S. Joshi, and H. G. Pruess. Free radicals and grape seed proanthocyanidin extract: importance in human health and disease prevention. Toxicology 148: 187-197, 2000.
11. Ben Amotz, A. and Y. Levy. Bioavailability of a natural isomer mixture compared with synthetic all-trans beta-carotene in human serum. Am.J.Clin.Nutr. 63: 729-734, 1996.
12. Bendich, A. and J. A. Olson. Biological actions of carotenoids. FASEB J. 3: 1927-1932, 1989.
13. Bovell-Benjamin, A. C., F. E. Viteri, and L. H. Allen. Iron absorption from ferrous bisglycinate and ferric trisglycinate in wholemaize is regulated by iron status. Am.J.Clin.Nutr. 71: 1563-1569, 2000.
14. Burton, G. W., M. G. Traber, R. V. Acuff, D. N. Walters, H. Kayden, L. Hughes, and K. U. Ingold. Human plasma and tissue alpha-tocopherol concentrations in response to supplementation with deuterated natural and synthetic vitamin E. Am.J.Clin.Nutr. 67: 669-684, 1998.
15. Chopra, R. K. and H. N. Bhagavan. Relative bioavailabilities of natural and synthetic vitamin E formulations containing mixed tocopherols in human subjects. Int.J.Vitam.Nutr.Res. 69: 92-95, 1999.
16. Christen, S., A. A. Woodall, M. K. Shigenaga, P. T. Southwell-Keely, M. W. Duncan, and B. N. Ames. gamma-tocopherol traps mutagenic electrophiles such as NOx and complements alpha- tocopherol: physiological implications. Proc.Natl.Acad.Sci.U.S.A 94: 3217-3222, 1997.
17. Di Carlo, G., N. Mascolo, A. A. Izzo, and F. Capasso. Flavonoids: old and new aspects of a class of natural therapeutic drugs. Life Sci. 65: 337-353, 1999.
18. Ferslew, K. E., R. V. Acuff, E. A. Daigneault, T. W. Woolley, and P. E. Stanton. Pharmacokinetics and bioavailability of the RRR and all racemic stereoisomers of alpha-tocopherol in humans after single oral administration. J.Clin.Pharmacol. 33: 84-88, 1993.
19. Garrison, R. H. and E. Somer. The Nutrition Desk Reference. New Canaan, Keats Publishing, Inc. 1990.
20. Gey, K. F., P. Puska, P. Jordan, and U. K. Moser. Am.J.Clin.Nutr. 53: 326S-334S, 1991.
21. Graff, D. J. Absorption of minerals compared with chelates made from various protein sources into rat jejunal slices in vitro. 1970. Salt Lake City. 1970. Ref Type: Conference Proceeding
22. Handelman, G. J., I. J. Machlin, K. Fitch, J. J. Weiter, and E. A. Dratz. J.Nutr. 115: 807-813, 1985.
23. Heaney, R. P., R. R. Recker, and C. M. Weaver. Absorbability of calcium sources: the limited role of solubility. Calcif.Tissue.Int. 46: 300-304, 1990.
24. Hoppe, P. P. and G. Krennrich. Bioavailability and potency of natural-source and all-racemic alpha-tocopherol in the human: a dispute. Eur.J.Nutr. 39: 183-193, 2000.
25. Jha, P., M. Flather, E. Lonn, M. Farkouth, and S. Yusuf. Ann.Intern.Med. 123: 860-872, 1995.
26. Kushi, L. H., A. R. Folsom, R. J. Prineas, P. J. Mink, Y. Wu, and R. M. Bostick. NEJM 334: 1156-1162, 1996.
27. La Casa, C., I. Villegas, d. l. L. Alarcon, V. Motilva, and M. J. Martin Calero. Evidence for protective and antioxidant properties of rutin, a natural flavone, against ethanol induced gastric lesions. J.Ethnopharmacol. 71: 45-53, 2000.
28. Linder, M. C., L. Wooten, P. Cervesa, S. Cotton, R. Shulze, and N. Lomeli. Copper Transport. Am.J.Clin.Nutr. 67(suppl): 965S-971S, 1998.
29. MacPhail, A. P., T. H. Bothwell, J. D. Torrance, D. P. Derman, R. W. Bezwoda, R. W. Charlton, and F. Mayet. Br.J.Nutr. 45: 215, 1891.
30. Middleton, E. Effect of plant flavonoids on immune and inflammatory cell function. Adv.Exp.Med.Biol. 439: 175- 182, 1998.
31. Moran, J. R. and H. L. Greene. The Gastrointestinal Tract: Regulator of Nutrient Absorption. In Shils, M. E., J. A. Olson, and M. hike, eds. Modern Nutrition in Health and Disease. Baltimore, Williams and Wilkins. 1994.
32. Ohrvall, M., G. Sundolf, and B. Vessby. J.Int.Med. 239: 111-117, 1996.
33. Paiva, S. A. and R. M. Russell. Beta-carotene and other carotenoids as antioxidants. J.Am.Coll.Nutr. 18: 426-433, 1999.
34. Pineda, O., H. D. Ashmead, J. M. Perez, and C. P. Lemus. Effectiveness of iron amino acid chelate on the treatment of iron deficiency anemia in adolescents. J.Appl.Nutr. 46: 2-13, 1994.
35. Ramaswamy, K. Intestinal absorption of water-soluble vitamins focus on "Molecular mechanism of the intestinal biotin transport process". Am.J.Physiol 277: C603-C604, 1999.
36. Rose, R. C. Water-soluble vitamin absorption in intestine. Annu.Rev.Physiol 42: 157-171, 1980.
37. Rose, R. C. Intestinal absorption of water-soluble vitamins. Proc.Soc.Exp.Biol.Med. 212: 191-198, 1996.
38. Theriault, A., J. T. Chao, Q. Wang, A. Gapor, and K. Adeli. Tocotrienol: a review of its therapeutic potential. Clin.Biochem. 32: 309-319, 1999.
39. Traber, M. G. Utilization of vitamin E. Biofactors 10: 115-120, 1999.
40. Vinson, J. A. and P. Bose. Comparative bioavailability of synthetic and natural vitamin C in guinea pigs. Nutr.Rep.Int. 27: 875-880, 1983.
41. Vinson, J. A. and P. Bose. Comparative bioavailability to humans of ascorbic acid alone or in a citrus extract. Am.J.Clin.Nutr. 48: 601-604, 1988.
42. Wapnir, R. A. Copper absorption and bioavailability. Am.J.Clin.Nutr 67: 1054S-1060S, 1998.
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