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Speciation, bioavailability, biopotency and functional markers for D vitamers

Project Code: N05011

21/09/2010

LGC
Lawrence, P

There is considerable interest in the dietary intake of vitamin D, its role in human health and the bioavailability and biological potency of vitamin D and its metabolites. Vitamin D status has been shown to be linked to a number of human diseases but its precise role and biological action is still not fully defined. Vitamin D deficiency is still of concern. Those most at risk are the elderly, young children, pregnant mothers and sectors of the Asian community.

The amount of vitamin D ingested varies widely (from <1 microgram to around 10 micrograms per day) depending upon the foods consumed, which are either naturally rich sources of vitamin D (eg oily fish & eggs) or have been fortified (eg margarine). Children older than four years and adults less than 65 years old in the UK, are generally considered to meet vitamin D requirements without specific need for dietary intake due to endogenous synthesis from exposure of the skin to strong sunlight. Despite this, vitamin D deficiency symptoms are increasing amongst vulnerable groups of the population.

There is a need to re-assess dietary intake values as the vitamin D content of certain foods (eg some meat and fish) has recently been shown to be higher than previously thought. This may be partly due to the presence of 25 hydroxy vitamin D3, which is thought to have a higher biological activity in humans (between 2 & 5 times that of vitamin D3). Although it has been known for many years that this is the main circulating form in humans, until recently it has not been possible to determine this metabolite in foods.

Further investigation is required to establish the bioavailability and biopotency of vitamin D in humans. Methods that will specifically determine vitamin D and its metabolites in food and sera are required

The project consisted of three work packages as follows:

1. To obtain data on the cholecalciferol (vitamin D3) and 25-hydroxy cholecalciferol (25-OHD3) content of imported, freshwater fish consumed by the Bangladeshi community in Whitechapel, London, so that the effect of dietary vitamin D intake could be correlated to earlier clinical study data.
2. To obtain information on the vitamin D3 and 25-OHD3 content of additional selected foods to supplement national food database data.
3.To develop and validate a method for the determination of 25-OHD3 in serum.
The data obtained supplements data contained in national food tables, informs the assessment of dietary vitamin D intake on an ’at-risk’ group of the population and provides a means of measuring vitamin D status in humans. Such information can be used to assess the bioavailability of vitamin D in future human feeding trials.

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