As part of the Food4Me pan-European project, a new sampling and analysis procedure for vitamin D has been developed. The technique enables unsupervised sampling of drops of blood from a fingertip onto a prepared card. A total of 3,778 valid measurements were made from 1,465 participants. The highest mean levels of vitamin D were found towards the end of July, whilst the lowest were towards the end of January. This is consistent with previous population survey data.
The Food4Me pan-European study was a randomized controlled trial (RCT) which had the aim of determining if personally targeted dietary advice can improve eating habits and health outcomes when compared with conventional, population-based, general guideline approaches. The project involved seven research centers in seven European countries with at least 220 participants attached to each research centre. The RCT had a total of 1,607 recruits aged between 18 and 79 years (2).
A new sampling and analysis procedure for vitamin D has been developed for this project (1). The technique enables unsupervised sampling of drops of blood from a fingertip onto a prepared card. Sampling was done at the beginning of the trial, then at three and six months after the beginning of the intervention. The participants were instructed to put five drops of blood within the circles on the test cards, then allow the spots to dry at room temperature before mailing them back to the test laboratory. The chromatographic analysis was made using an Ascentis Express C18 column (Supelco) with a detection unit consisting of an AB Sciex 5500 Qtrap instrument (in APPI positive mode and MRM scan type at unit resolution). A total of 3,778 valid measurements were made from 1,465 participants.
Whilst the technique was not as accurate as whole blood samples analyzed by the standard liquid chromatograph-MS/MS, the accuracy level was considered sufficient for use in a field study such as Food4Me. (The method gave a deviation of 18% between measured and nominal values). The study demonstrated that vitamin D levels were considerably higher in the summer compared with the winter (67.1 to 92.1 v. 38.0 to 63.0 nmol/l) with the biggest seasonal variation being noted in the inhabitants of Germany, who had a mean of 92.1 nmol/l in summer and 41.9 nmol/l in winter.
The Food4Me project is the largest study of its type to use a dried blood spot sampling technique for vitamin D testing. The assay was developed using careful calibration procedures. This resulted in analytical values only marginally less accurate than those achieved with the gold standard chromatograph-MS/MS using whole blood. This new, simplified sampling/testing procedure using dried blood spots will enable the number of participants of future studies looking at vitamin D status to be considerably enlarged.