25-Hydroxyvitamin D – Should labs be measuring it?

Perception of vitamin D supplementation as a panacea for good health continues. Media coverage proclaims widespread vitamin D deficiency, with supplementation needed to prevent disease,1 despite most research covered being epidemiological association studies beset by confounding and reverse causality. Commercial interests promoting supplementation influence advocacy organizations and academia.2 However, high-quality evidence indicates that vitamin D supplementation does not improve musculoskeletal outcomes, other than preventing rickets and osteomalacia in high-risk groups.3,4 Effects on non-musculoskeletal outcomes, such as cancer, cardiovascular disease and mortality, are unconvincing.3,4 Nevertheless, vitamin D has become medicalized,5 driving demands for predominantly inappropriate measurement of 25-hydroxyvitamin D (25OHD), the metabolite best reflecting tissue stores.6–8 Most Scottish laboratories limit testing to one/year/patient, but >1% of the population have 25OHD measured annually (Karen Smith, personal communication). Between 2008 and 2014, 25OHD testing in English children in primary care rose from 43/100,000 to 768/100,000 with an estimated cost in 2014 of £1.69 million.7