Effect of habitual calcium intake on dietary vitamin D requirements in adults

If dietary calcium intake is low and serum calcium concentrations decrease, the compensatory metabolic response is the accelerated conversion of 25-hydroxyvitamin D [25(OH)D] to 1,25-dihydroxyvitamin D (via parathyroid hormone), so as to normalize serum calcium levels (1). The aim of this study was to test this hypothesis using relevant data from our previously published vitamin D intervention studies in 20–40 y olds (3) and 64+ y olds (4) as well as an updated version of our recent meta-regression analysis (5), all of which up to now have not included dietary calcium intake as a possible additional determinant of vitamin D requirements. [...]post-hoc analysis seems to suggest that a habitual calcium intake less than 700 mg/d may lead to a more blunted response of winter serum 25(OH)D to increased vitamin D intake in older adults.