Moreover, another form of vitamin E, gamma-tocopherol, also tended to reduce the absorption of the alpha-form, the researchers report in the European Journal of Clinical Nutrition. The results could force a rethink for vitamin formulations in order to maximise the nutritional quality of the supplements. Presently, alpha-tocopherol is often combined with other antioxidants and other forms of vitamin E. An in vitro study showed that the polyphenol naringenin and a carotenoids mixture (lycopene, beta-carotene and lutein) significantly impaired the absorption of alpha-tocopherol across a cell system model of the intestine (Caco-2 cells). (R,R,R)-alpha-tocopherol is a fat-soluble antioxidant vitamin generally ingested with other dietary antioxidants. The researchers, from France's Institut National de la Santé Et de la Recherche Médicale (INSERM) U476 in Marseille, followed the in vitro study with a small human study with eight male volunteers.
The men consumed an alpha-tocopherol-rich meal (24 mg in sunflower oil) in the presence of two doses of lutein (18 or 36 mg). The highest dose of lutein had the greatest impact on the post-meal alpha-tocopherol absorption measurement (616280 versus 1001287 nanomoles per litre per hour), said the researchers. "The observed extent of reduction (38 per cent) supported the inhibitory effect of carotenoids observed in the Caco-2 experiments," wrote the researchers, led by Patrick Borel. On the other hand, Borel and co-workers reported some potentially good news for formulators. Vitamin C did not impact on the absorption of alpha-tocopherol, while the polyphenols gallic acid, caffeic acid, and (+)-catechin also had no effect. This suggested that all of these antioxidants could be included in formulations with alpha-tocopherol without detrimental effects on absorption. Further study is needed to confirm these results, with additional human absorption studies and mechanistic research to highlight how the other nutrients may impact negatively on alpha-tocopherol absorption.
There are eight forms of vitamin E: four tocopherols (alpha, beta, gamma, delta) and four tocotrienols (alpha, beta, gamma, delta). Alpha-tocopherol (alpha-Toc) is the main source found in supplements and in the European diet, while gamma-tocopherol (gamma-Toc) is the most common form in the American diet. Source: European Journal of Clinical Nutrition Volume 61, Pages 1167-1173, doi:10.1038/sj.ejcn.1602635 "Effect of the main dietary antioxidants (carotenoids, gamma-tocopherol, polyphenols, and vitamin C) on alpha-tocopherol absorption"
Authors: E. Reboul, S. Thap, E. Perrot, M.-J. Amiot, D. Lairon and P. Borel