25-Hydroxyvitamin D Measurement in Human Hair: Results from a Proof-of-Concept study.
Zgaga, L, Laird, E, Healy, M
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Vitamin-D deficiency is now considered to effect over 1 billion people world-wide and has known health implications including bone pathologies, immune dysfunction and metabolic diseases. It is thought that vitamin-D deficiency is increasing amongst the population due to our indoor lifestyles and increased use of sunscreens. The current method used to determine vitamin-D status is by measuring the concentration within blood circulation. Although considered accurate, this method can prove inconvenient and costly, especially for those requiring repeat or regular monitoring. A far simpler means of measurement is through hair analysis, although this method is in its infantry. The aim of this study was to investigate whether this method shows consistent markers in vitamin-D status which correlate to those of blood samples and whether hair analysis has potential for further research. The subjects in this study were the three authors who compared vitamin-D markers within their own hair to the markers within their blood serum concentrations. They found that although it is not possible to rely solely on hair analysis to measure vitamin-D status, it is possible to gain a picture of vitamin-D status historically, which can aid epidemiological research. Supplemental intake could also be monitored through longitudinal methods. Whilst the results were varied and inconclusive, the authors do suggest that there is scope for future research. Variations need to be accounted for, such as hair colour, age related differences plus methods of extracting the vitamin from the hair shaft.
Vitamin D deficiency has been implicated in numerous human diseases leading to an increased interest in assessing vitamin D status. Consequentially, the number of requests for vitamin D measurement keeps dramatically increasing year-on-year. Currently, the recognised best marker of vitamin D status is the concentration of the 25-hydroxyvitamin D (25(OH)D₃) in the blood circulation. While providing an accurate estimate of vitamin D status at the point in time of sampling, it cannot account for the high variability of 25(OH)D₃ concentration. In this proof of concept study we set out to provide evidence that 25(OH)D₃ can be extracted from hair samples in a similar fashion to steroid hormones. Two of the authors (L.Z. and M.H.) provided hair samples harvested from the crown area of the scalp and the third author (E.L.) provided beard samples. These samples, cut into 1 cm lengths, were weighed, washed and dried. 25(OH)D was extracted using a previously published steroid hormones extraction procedure. Blood samples were taken from the subjects at the same time all tissue samples were analysed using liquid-chromatography mass spectrometry. Hair samples showed presence of quantifiable 25(OH)D₃ with concentrations ranging from 11.9⁻911 pg/mg. The beard sample had a concentration of 231 pg/mg. Serum levels of 25(OH)D₃ ranged from 72⁻78 nmol/L. The results presented here confirm the feasibility of measuring 25(OH)D₃ in hair samples. The findings warrant further validation and development and have the potential to yield valuable information relating to temporal trends in vitamin D physiology.