Collectively , these outcomes support a volumetric dilution of vitamin D. The slopes of the respective regression lines , however , indicate a smaller increase in 25OHD than would be expected from a direct mobilization of stores into the circulation .
Hence , sequestration of 25OHD and its conversion to inactive metabolites would also play a role .
The purpose of this review was to confirm a volumetric dilution of vitamin D in obesity .
It was based on the hypothesis that weight loss , particularly fat loss , would increase serum 25-hydroxyvitamin D ( 25OHD ) in the obese .
Dairy calcium intake, serum vitamin D, and successful weight loss.
BACKGROUND The role of dairy calcium intake and serum vitamin D concentrations in weight loss is controversial . OBJECTIVE The objective was to assess the association of dairy calcium intake and serum vitamin D with weight loss . DESIGN We analyzed data from participants in the 2-y Dietary Intervention R and omized Controlled Trial ( DIRECT ) [ n = 322 ; mean body mass index ( BMI ; in kg/m² ) : 31 ; mean age : 52 y ] . A representative sample ( n = 126 ) was followed for 6 mo for serum vitamin D changes . RESULTS Baseline serum 25-hydroxyvitamin D [ 25(OH)D ] concentrations decreased significantly across the tertiles of baseline BMI ( 25.6 ± 8.0 , 24.1 ± 8.9 , and 22.9 ± 6.8 ng/mL , respectively ; P for trend = 0.02 ) . Baseline concentrations of vitamin D and dairy calcium  intake were not associated with subsequent weight loss . However , in repeated- measures models adjusted for age , sex , baseline BMI , total fat intake , and diet group assignment , higher 6-mo tertile levels of dairy calcium intake ( median for tertiles : 156.5 , 358.0 , and 582.9 mg/d , respectively ) and serum 25(OH)D ( 14.5 , 21.2 , and 30.2 ng/mL , respectively ) were associated with increased weight loss across the 2-y intervention ( -3.3 , -3.5 , and -5.3 kg , respectively , for dairy calcium ; P = 0.043 ; -3.1 , -3.8 , and -5.6 kg , respectively , for vitamin D ; P = 0.013 ) . In a multivariate logistic regression adjusted simultaneously for age , sex , baseline BMI , total fat intake , diet group , vitamin D concentration , and dairy calcium , an increase of 1 SD in  dairy calcium intake increased the likelihood of weight loss of > 4.5 kg in the preceding 6 mo [ odds ratio ( OR ) : 1.45 ; P = 0.046 ] . A similar increase was seen for serum 25(OH)D at the 6-mo point ( OR : 1.7 ; P = 0.009 ) . CONCLUSION Our study suggests that both higher dairy calcium intake and increased serum vitamin D are related to greater diet-induced weight loss . This trial was registered at clinical trials.gov as NCT00160108
Collectively , these outcomes support a volumetric dilution of vitamin D. The slopes of the respective regression lines , however , indicate a smaller increase in 25OHD than would be expected from a direct mobilization of stores into the circulation .
Hence , sequestration of 25OHD and its conversion to inactive metabolites would also play a role .
The purpose of this review was to confirm a volumetric dilution of vitamin D in obesity .
It was based on the hypothesis that weight loss , particularly fat loss , would increase serum 25-hydroxyvitamin D ( 25OHD ) in the obese .