ARS | Publication request: Calcium absorption is not consistently enhanced by maintaining serum 25-hydroxyvitamin D levels

Submitted to: Pediatric Academic Society
Publication Type: Abstract Only
Publication Acceptance Date: February 17, 2009
Publication Date: May 4, 2009
Citation: Abrams, S.A., Hicks, P.D., Hawthorne, K.M. 2009. Calcium absorption is not consistently enhanced by maintaining serum 25-hydroxyvitamin D levels > 50 or 80 nmol/L [abstract]. Pediatric Academic Society. Abstract no. 4545.1.

Technical Abstract: Increasing serum 25-hydroxyvitamin D (25-OHD) in adults may enhance calcium absorption (Ca-abs). Targeting of 25-OHD values for the entire population has been widely advocated recently with goals of 25-OHD of at least 50 or 80 nmol/L advocated. There are few pediatric data that relate 25-OHD to Ca-abs on which to evaluate target 25-OHD values. Our objective was to evaluate the relationship between 25-OHD and Ca-abs in a large cohort of school-age children and adolescents. We evaluated data from 439 Ca-abs measurements performed using dual-tracer stable isotope techniques conducted at our center over a 15-year period in 251 healthy children, 4.9 to 16.7 yrs of age. Serum 25-OHD ranged from 28 to 197 nmol/L (Mean 85 +/- 2 nmol/L). Total Ca-abs (intake times fractional absorption) was significantly correlated to 25-OHD in the whole population, r = 0.16, P = 0.001. This relationship was closer in the 197 studies in early puberty (Tanner 2 or 3), r = 0.35, P < 0.001 and not significant in pre- or late-pubertal subjects. For the whole population (n =439), there was no close correlation between 25-OHD and fractional absorption of calcium (r = 0.03, P = 0.46). In a general linear model with calcium intake, pubertal status, gender and race as covariates, fractional absorption was not significantly related to 25-OHD (p = 0.34) but was significantly (negatively) associated with calcium intake, P = 0.03. Fractional absorption of calcium adjusted for calcium intake was significantly higher at 25-OHD of 28-50 nmol/L, (0.344 +/- 0.019) compared to 25-OHD of 50-80 nmol/l (0.280 +/- 0.014) or 25-OHD > 80 nmol/L (0.297 +/- 0.015), P < 0.01 for each, suggesting adaptation to moderately low 25-OHD values. We found a small effect of higher 25-OHD values on total but not fractional Ca-abs primarily during early puberty. This effect was inconsistent and not a large factor in determining Ca-abs. Adaptation to moderately low 25-OHD (28-50 nmol/L) occurred to support Ca-abs. Our data do not provide support for achieving a 25-OHD above any specific value in prepubertal school-age children based on optimizing calcium absorption. The overall costs and benefits of assessment and intervention strategies to achieve any preset 25-OHD in school-age children should be considered before public policy interventions are put in place to achieve them.