Do genetic polymorphisms in a beta-carotene metabolising key enzyme influence dietary vitamin A requirements?
Vitamin A (retinol) is an essential nutrient for vision, embryonic development, maturity of organs, cellular proliferation andthe immune response. It is obtained from the diet per se or through provitamin A sources that are cleaved enzymatically
in the body to produce retinol. Vitamin A deficiency occurs largely due to increases in physiological requirements (growth, pregnancy, lactation, infection) together with a low dietary intake.
Currently, the mean daily intake of vitamin A is below the recommended intake levels for men and women aged 19 to 24 years. This means that young individuals in the UK rely to over 50% on provitamin A sources, beta-carotene being the main one, to cover their vitamin A needs. Since a significant proportion of young British individuals have a low vitamin A intake and since the Expert Group on Vitamins and Minerals has recommended to limit the use of beta-carotene in food supplements, there is growing concern that young men and women in the UK might develop subclinical deficiencies, therefore increasing their susceptibility to infectious diseases. This concern is especially valid for young pregnant women who will experience a higher physiological need for vitamin A.
Given the fact that a high proportion of the British population relies on beta carotene to cover their vitamin A needs, it is important to note that the amount of retinol produced after ingestion and conversion of beta-carotene is highly variable between healthy individuals. Several studies have shown a large disparity between individuals who are efficient or inefficient converters of beta-carotene, with variations of up to 8-fold. It is possible that the observed differences in obtaining retinol from beta-carotene may be due to genetic polymorphisms in genes involved in aspects of beta-carotene conversion. Indeed, results from our laboratory have shown that two genetic variants exists in the key enzyme responsible for beta-carotene conversion.
Newcastle and North Tyneside Local Research Ethics Committees approved on the 19th May 2009 (ref: 09/H0904/20)
Single centre non-randomised interventional trial
Primary study design
Secondary study design
Non randomised controlled trial
Patient information sheet
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Topic: Generic Health Relevance and Cross Cutting Themes; Subtopic: Generic Health Relevance (all Subtopics); Disease: Public Health Research
The intervention will last 14 days. However, first contact with the study participants will be 2 months prior to the start of the intervention to explain the study. A capsule containing 2 mg dose of beta-carotene and 1 mg retinyl acetate stable isotope will be orally adminstered to volunteers on day 1. Blood samples will be drawn at 7 time points on day 1, with subsequent samples being taken on days 2, 3, 7, and 14.
Primary outcome measures
Blood concentrations of administered beta-carotene/retinyl acetate, and derived metabolites. Primary outcome measures will be taken at 0, 2, 4, 6, 8, 12 hours on day 1. Then at days 2, 3, 7, and 14.
Secondary outcome measures
No secondary outcome measures
Overall trial start date
Overall trial end date
Participant inclusion criteria
1. Aged 18 - 45 years
2. Generally fit and healthy adults
3. Males and females
Target number of participants
Planned sample size: 200
Participant exclusion criteria
2. Pregnant females
4. Liver disease
5. Gastrointestinal disorders
Recruitment start date
Recruitment end date
Countries of recruitment
Trial participating centre
School of Agriculture, Food and Rural Development (AFRD)
Newcastle upon Tyne
Newcastle University (UK)
School of Agriculture Food and Rural Department
Newcastle Upon Tyne
Biotechnology and Biological Science Research Council (BBSRC) (UK)
Funding Body Type
Funding Body Subtype
Results and Publications
Publication and dissemination plan
Not provided at time of registration
Intention to publish date
Participant level data
Not provided at time of registration
Results - basic reporting