Distribution analysis of vitamin D highlights differences in population subgroups: preliminary observations from a pilot study in UK adults

There is no consensus between authors on the definition of a replete or deficient vitamin D state. Our aim was to describe a suitable method that could be used to compare vitamin D data in subject groups with small or large numbers. Two hundred and forty indigenous asymptomatic, non-pregnant adult subjects recruited from a single-consultation outpatient attendance with normal biochemistry, represented a sample of our inner city district population. 25-hydroxyvitamin D (25,OHD3) levels were measured to illustrate the effects of season, sex and ethnic group on vitamin D levels and subjected to distribution analysis. This method quantifies as a percentage the distribution of 25,OHD3 concentrations (observed concentration. OC) in pooled group data. The data can be expressed as distribution frequency domains or cumulative frequency ogives (0-100%) or transformed into discrete linear probits. amenable to regression analysis. An estimate of the OC50, (mid-point) and upper (either OC75 or OC95) or lower (either OC25 or OC5) range or at any other frequency between subject groups can be compared. A marked difference in 25,OHD3 levels between Asian and non-Asian asymptomatic adult subjects was seen during both seasons. 25,OHD3 deficiency was defined as at or below the OC25 for the non-Asian group (for both sexes: winter <13.36 ng/ml, summer <13.38 ng/ml). The majority of Asians of both sexes were 25,OHD3 deficient (winter 94 0, summer 82 0). The distribution analysis provides an easy technique to compare 25,OHD3 status of different subject groups, allowing the description of populations using either longitudinal or cross-sectional data. This method may offer a way of describing 25,OHD3 deficiency between observers worldwide.