The Bioavailability of Various Oral Forms of Folate Supplementation in Healthy Populations and Animal Models: A Systematic Review

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Journal Article
Journal of Alternative and Complementary Medicine, 2019, 25 (2), pp. 169 - 180
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© 2019, Mary Ann Liebert, Inc. Background and aims: Folate is an essential nutrient required for many different functions in the body. It is particularly important for DNA synthesis, immune functions, and during pregnancy. Folate supplements are commonly prescribed by health professionals for a number of different conditions, however, the absorption of the different derivatives remains unclear. The aim of this review was to assess the bioavailability of various forms of folate supplements in healthy populations and animal models. Methods: A systematic literature review was conducted of original research, which assessed the bioavailability of different oral forms of folate in healthy adults or animal models. The following databases were searched: PubMed (U.S. National Library of Medicine), ProQuest Medical Collection (ProQuest) and ScienceDirect (Elsevier) up to March 30, 2017. The inclusion criteria consisted of both animal and human research, no disease state or condition, and assessed levels after an intervention of a folate derivative. Results: A total of 23 studies out of 5226 met the full inclusion criteria. Of these, 4 were animal studies and 19 were human studies. There was variation in supplement forms used with the most commonly tested being folic acid followed by 5-methylenetetrahydrofolate (5-MTHF). Dosages ranged from 25 μg up to 200 mg. Only three studies found a statistically significant difference in folate bioavailability when evaluating different supplement forms. These studies found 5-MTHF to be more effective at increasing folate levels in participants. Conclusions: This review has found a number of methodological limitations and conflicting results. Only three out of the 23 studies assessed found a statistically significant difference between different supplemental forms of folate. Quality absorption studies assessing the bioavailability of oral folate supplements are crucial if clinicians are to make effective evidence-based recommendations. More research is required for greater clarification regarding the bioavailability of these supplements.
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