N05027: The use of deuterated tocopherol to study vitamin E metabolism in normal subjects - impact of diet and supplementation regimes
Thursday 3 April 2003
This research project aims to improve understanding of the benefits, and risks, associated with taking antioxidants in increased quantities.
Background
Dietary antioxidants, or micronutrients required for their synthesis, are widely acknowledged to be essential components of a 'healthy diet'. Following intensive investigation of antioxidant function the concept has arisen that the many antioxidants and micronutrients act synergistically within a network. Clearly, the benefit of such a network is that individual components may at times compensate for lack of other constituents. On a negative note, supplementation with large amounts of one antioxidant may adversely affect other members of the integrated network. Although a number of such interactions have been identified in vitro no evidence exists for such associations within the human body.
Rationale and Objectives
Clearly, if synergism does exist it will be important to take it into consideration when setting dietary requirements for individual antioxidants and when advising on the level of supplementation appropriate. The purpose of this project was to examine these issues.
Research Approach
A range of antioxidants (alpha-tocopherol, beta-carotene, co-enzyme Q and glutathione peroxidase) and an antioxidant-associated micronutrient (selenium) were determined in the same blood samples. These samples were collected as part of a previous contract N05009 and had been stored in conditions which minimised a loss in antioxidant activity. A particular strength of this study was the availability of two samples, collected 3 weeks apart, from each of 60 subjects. Examination of these samples allowed us to address both the repeatability of each measure within subjects as well as examine for any associations between the various antioxidants.
Additional Information
This project is an extension to N05009.
Results and findings
Key results obtained
Of the five antioxidant determinations made, all were found to be stable across the 3-week sampling period. This finding will be of considerable use during the interpretation of other data collected within this timeframe as well as in the design of future studies. Following this, we proceed to search for associations between any of these antioxidant measures. As multiple comparisons of the data were undertaken we reduced the level of acceptable significance to 1% to help exclude any spurious associations. Using this criterion, two significant associations were identified within the dataset. The first was a positive association between blood selenium concentrations and glutathione peroxidase activity. The second was a positive association between coenzyme Q and vitamin C concentrations.
What do these findings imply?
Selenium is required at the active site of glutathione peroxidase, hence the association between selenium and glutathione peroxidase was expected. Although not direct evidence of interdependence it supports previous such observations. Given the present worry about selenium availability from the UK diet, the clear implication of this finding is that glutathione peroxidase activity in normal healthy adults is limited by the availability of this micronutrient. The second observation, a positive association between coenzyme Q and vitamin C, has to the best of my knowledge not been previously reported. Vitamin C and coenzyme Q are important antioxidants and interestingly, both can regenerate oxidised vitamin E. The observation that the concentration of these two antioxidants is related in healthy subjects provides evidence of a protective link between these dietary components.
Contact: Dr Alison Tedstone
Tel: 020 7276 8929
Email: alison.tedstone@foodstandards.gsi.gov.uk