The ratio of serum 24,25-dihydroxyvitamin D3 to 25-hydroxyvitamin D3 is predictive of 25-hydroxyvitamin D3 response to vitamin D3 supplementation

Lifestyle and Other Factors Explain One-Half of the Variability in the Serum 25-Hydroxyvitamin D Response to Cholecalciferol Supplementation in Healthy Adults

“…The inconsistencies seen across studies may reflect small sample sizes, as well as differences in the covariates collected and how they were measured. Age and race were not associated with response to supplementation in our study or in several others (21,27,(45)(46)(47)(48)(49)(50)(51). Several variables (being female, greater physical activity, wearing long pants and sleeves while outdoors, and personal vitamin D supplement use) contributed significantly to both baseline and response models; this suggests either that these factors are independent determinants of both baseline serum 25(OH)D concentration and response to supplementation, or that they have residual effects in the response model because they are imperfectly represented by baseline serum 25(OH)D concentration, e.g., because of measurement error.…”

Assessment of vitamin D status – a changing landscape

“…CYP24A1 is, at least in part, regulated by VDR [112,114] [115]. A potential value of VMR in monitoring the effectiveness of vitamin D supplementation has also been shown by others [116].…”

Significance of Serum 24,25-Dihydroxyvitamin D in the Assessment of Vitamin D Status: A Double-edged Sword?

“…Serum total 25(OH)D and 24,25(OH) 2 D 3 increases and decreases, respectively, in the vitamin D 3 and placebo groups were of magnitudes similar to those with calcium intakes Ͻ700 and Ͼ1000 mg/day (4 ). In the present study, since there was no interaction with dietary calcium (P ϭ 0.2), we examined the effect of vitamin D 3 We selected 4 baseline serum samples from the VitD-Ca RCT for measurement of serum total 25(OH)D by immunoassay (Octeia) before and after spiking the samples with the R isomer 24,25(OH) 2 Table 2). The increase in serum total 25(OH)D in spiked samples, as measured by immunoassay, ranged from 14 to 38 nmol/L and far exceeded the concentration of spiked or total (spike plus natural content) serum 24, 25(OH) 2 D 3 present (Table 2) Table 2).…”

“…Not unsurprisingly, assessment of serum 24,25(OH) 2 D, particularly when expressed as a molar ratio to 25(OH)D, has found favor as an index of vitamin D deficiency and catabolism in healthy individuals (2)(3)(4)(5), as well as in those with rare genetic mutations in the CYP24A1 gene (5,6 ). The ratio of 24,25(OH) 2 D to 25(OH)D may also be an indicator of response to vitamin D supplementation (3 ) and may help to explain some of the well-documented interindividual differences in response of serum 25(OH)D to the same administered dose of vitamin D. Older data from animal experiments also suggest that 24,25(OH) 2 D [or the 24-hydroxylated product of 1,25(OH) 2 D 3 , 1,24,25(OH) 3 D 3 ] may stimulate intestinal calcium absorption and bone calcium mobilization (6,7 ). More recently, there is evidence for a role in fracture healing (8,9 ).…”