New standard for vitamin D test promises more accurate results
Writing in the journal Analytical Chemistry, researchers from the US National Institute of Standards and Technology (NIST) and the National Institutes of Health’s Office of Dietary Supplements (NIH-ODS), report the development of a Standard Reference Material (SRM) for the determination of vitamin D in the form of 25-hydroxyvitamin D [25(OH)D] in human serum.
The researchers, led by Karen Phinney of the NIST, explained that renewed interest in vitamin D status due to increasing interest in its links to diseases like rickets, osteoporosis, multiple sclerosis and Parkinson's disease, mean that researchers need an accurate way to measure its levels in the blood.
They noted that the current method for testing vitamin D – by detecting levels of a vitamin D metabolite called 25(OH)D – does not always provide accurate or reliable results.
To help researchers and industry to assess vitamin D levels with consistent and accurate methods, the team developed a Standard Reference Material called SRM 972 – the first certified reference material for the determination of the metabolite in human serum (a component of blood).
"This reference material provides a mechanism to ensure measurement accuracy and comparability and represents a first step toward standardization of 25(OH)D measurements," said Phinney and her team.
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. Both D3 and D2 precursors are transformed in the liver and kidneys into 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body.
The essential role of vitamin D in bone metabolism and calcium homeostasis has been known for many years, however recently the vitamin has been the subject of renewed interest – due to its functions in the regulation of the cell cycle, cell death and differentiation.
The authors noted that both epidemiological data and animal model studies “have pointed toward a link between vitamin D status and cancer risk,” in addition to other serious illnesses including multiple sclerosis and Parkinson's disease.
Although 1,25(OH)2D is the physiologically active metabolite of vitamin D, the research team explained that it has limited use as an indicator of vitamin D status because its levels in the body are influenced by concentrations of both other compounds including parathyroid hormone (PTH) and calcium.
“Similarly, vitamin D is also a poor marker of vitamin D status because it is rapidly hydroxylated to form 25(OH)D,” said Phinney and her team.
In contrast, 25(OH)D is not rapidly broken down, and as such this has become a preferred indicator of vitamin D nutritional status.
However the team noted that there are several important factors “that must be considered in the measurement of 25(OH)D,” including the realisation that the compound is generally bound to protein that must be removed before analysis.
In addition, they warned that the analysis method should respond equally to metabolites of both forms of vitamin D, even if concentrations of 25(OH)D2 and 25(OH)D3 are not reported separately.
The research paper outlining the newly developed, and ‘much-needed’, reference material can be found by clicking here.
Source: Analytical Chemistry
Volume 84, Issue 2, Pages 956–962, doi: 10.1021/ac202047n
“Development and Certification of a Standard Reference Material for Vitamin D Metabolites in Human Serum”
Authors: K.W. Phinney, M. Bedner, S.S.-C. Tai, V.V. Vamathevan et al