Bioavailability of natural versus synthetic B vitamins and their effects on metabolic processes

Abstract

Owing to the widespread use of vitamin supplements to prevent and compensate for deficiencies, the equivalence of natural versus synthetic vitamins with respect to their bioavailability and metabolic influence is discussed controversially. Thirty healthy female (n=22) and male participants (n=8) were investigated in a randomized, double-blind, cross-over study over a supplementation period of 6 weeks for each condition. The participants received a daily dose of a complex of the 8 natural B vitamins (group N), determined by the natural composition of quinoa seedlings, resp. synthetic B vitamins (group S), both corresponding to about 2.5 times the Recommended Dietary Allowance (RDA) of the national nutrition board. The primary criterion under investigation was changes in the blood levels of the individual B vitamins. Secondary criteria were the influence of both B complexes on homocysteine, antioxidant status, polyphenols, peroxide loading and peroxidase activity. Compared to baseline values, serum levels of all B vitamins measured increased: Vitamins B1 (N +23%; S +27%), B2 (N +14%; S +13%), B6 (N +101%; S +101%), B9 (N +86%; S +153%) and B12 (N +16%) were elevated at the end of the first supplementation period (p < 0.05), while serum levels of vitamins B1, B9 and B12 remained elevated compared to baseline even after the 2-week washout phase. During the second supplementation period, the vitamin concentrations in group N, with the exception of vitamin B1, could be increased once again (p < 0.05). In contrast, in group S only for vitamins B2 and B12 substantial increases (p < 0.05) were found. The influence of B vitamins on metabolic parameters such as homocysteine and polyphenols, which were markedly reduced, was also clearly measurable; however, total antioxidant capacity and peroxidase activity increased. The peroxide concentration remained almost unchanged in both groups. This clinical pilot study showed comparable bioavailability for both natural and synthetic B vitamins, with a 2.5-fold concentration of the RDA. Both vitamin B preparations showed a clear influence on metabolic parameters, whereas that of the natural B vitamins tended to have a slightly stronger effect than the synthetic analogues.