Low free 25-hydroxyvitamin D and high vitamin D binding protein and parathyroid hormone in obese Caucasians. A complex association with bone?

Background Studies have shown altered vitamin D metabolism in obesity. We assessed differences between obese and normal-weight subjects in total, free, and bioavailable 25-hydroxyvitamin D (25(OH) D, 25(OH) D-Free, and 25(OH) D-Bio, respectively), vitamin D binding protein (DBP), parathyroid hormone (PTH) and bone traits. Methods 595 37-47-year-old healthy Finnish men and women stratified by BMI were examined in this cross-sectional study. Background characteristic and intakes of vitamin D and calcium were collected. The concentrations of 25(OH) D, PTH, DBP, albumin and bone turnover markers were determined from blood. 25(OH) D-Free and 25(OH) D-Bio were calculated. pQCT was performed at radius and tibia. Results Mean +/- SE (ANCOVA) 25(OH) D-Free (10.8 +/- 0.6 vs 12.9 +/- 0.4 nmol/L; P = 0.008) and 25(OH) DBio (4.1 +/- 0.3 vs 5.1 +/- 0.1 nmol/L; P = 0.003) were lower in obese than in normal-weight women. In men, 25(OH) D (48.0 +/- 2.4 vs 56.4 +/- 2.0 nmol/L, P = 0.003), 25(OH) D-Free (10.3 +/- 0.7 vs 12.5 +/- 0.6 pmol/L; P = 0.044) and 25(OH) D-Bio (4.2 +/- 0.3 vs 5.1 +/- 0.2 nmol/L; P = 0.032) were lower in obese. Similarly in all subjects, 25(OH) D, 25(OH) D-Free and 25(OH) D-Bio were lower in obese (P Conclusions The associations between BMI and 25(OH) D, 25(OH) D-Free, and 25(OH) D-Bio, DBP, and PTH suggest that obese subjects may differ from normal-weight subjects in vitamin D metabolism. BMI associated positively with trabecular bone traits and CSI in our study, and slightly negatively with cortical bone traits. Surprisingly, there was a negative association of free and bioavailable 25(OH) D and some of the bone traits in obese women.Peer reviewe

Vitamin D in women of reproductive age and during pregnancy - Focus on intake, status and adiposity

Vitamin D is attained either through synthesis in the skin by sun exposure or through diet. Vitamin D status is important for skeletal health but optimal vitamin D status may also be important in the development of other diseases such as type 2 diabetes, gestational diabetes, preeclampsia, and cancer. Circulating vitamin D is known to be decreased in obese compared to non-obese individuals. There is a lack of documented knowledge on vitamin D status and intake in Swedish women of reproductive age and during pregnancy. The aim of this thesis was to compare vitamin D status and intake between obese and normal-weight women. In a cross-sectional study in women of reproductive age and in a longitudinal study during pregnancy, blood samples, adipose tissue biopsies, and information on dietary intake were collected. Data on lifestyle including physical activity and sun exposure were also collected. Vitamin D status, measured as serum 25-hydroxyvitamin D [25(OH)D], was lower in obese women of reproductive age compared with normal-weight women. In contrast, circulating vitamin D-binding protein was higher in the obese women. Despite reporting a higher vitamin D intake, the obese pregnant women had lower serum 25(OH)D compared with normal-weight women in early pregnancy. A higher proportion of the obese compared with normal-weight women had 25(OH)D concentrations that might be defined as insufficient. Circulating 25(OH)D concentrations below 25 nmol/L were uncommon in both pregnant and non-pregnant women. Dietary vitamin D intake was between 7.2 and 8.8 µg/day during pregnancy and in non-pregnant obese and normal-weight women, and a major part did not reach national dietary recommendations. There were no major differences in vitamin D intake between obese and normal-weight women. Vitamin D and its metabolites were detected in adipose tissue and were localized in the lipid droplet in the adipocyte. The present studies show that Swedish obese women of reproductive age and during pregnancy have lower circulating 25(OH)D compared with normal-weight women but few had very low concentrations. However, what effects an increased circulating 25(OH)D would have on long-term health in obese individuals is yet to be studied. The fact that obese women had higher circulating vitamin D-binding protein is interesting and should be further examined to clarify why, and what impact that may have on the action of vitamin D. We found no evidence of a lower vitamin D intake in obese women, thus, the intake was not contributing to the lower circulating 25(OH)D. Many women do not reach the recommendations for vitamin D intake. Actions should be taken to improve dietary intake of vitamin D in women of reproductive age and during pregnancy, this might have future implications not only for women’s health but for generations to come. Intervention studies are urgently needed to explore the effect of vitamin D status and intake during pregnancy and in obese subjects

Relationship of serum Vitamin D concentrations with Adipokines and Cardiometabolic risk among non-Hispanic black type 2 diabetic and non-diabetic subjects: a cross-sectional study

Abstract Background To report the association of serum 25-hydroxyvitamin D [25(OH)D] and its association with adipokines and cardiometabolic risk factors in Haitian Americans (HA) and African Americans (AA) by ethnicity and type 2 diabetes (T2D) status. Methods A cross-sectional study in 197 HA (92 with T2D and 102 without T2D) and 200 AA (97 with T2D and 103 without T2D) recruited in South Florida. Serum 25(OH)D concentrations and adipokines were analyzed by ELISA and cardiometabolic risk factors were indexed by obesity, glycemic control, insulin sensitivity, lipid profile, and blood pressure. Results Controlling for age, BMI, energy intake, smoking status and HOMA2-IR in multivariate linear regression analyses, serum 25(OH)D concentrations were significantly associated with WC (R2 = 0.760, B = − 0.092, P = 0.027), HbA1C (R2 = 0.142, B = − 0.012, P = 0.010), and TG (R2 = 0.159, B = − 1.192, P = 0.003) in only HA without T2D. While serum 25(OH)D concentrations were significantly associated with TC (R2 = 0.168, B = − 0.329, P = 0.040), log leptin (R2 = 0.544, B = − 0.007, P = 0.021), and adiponectin (R2 = 0.144, B = 0.111, P = 0.033), but slightly associated with LDL-c (R2 = 0.133, B = − 0.278, P = 0.064) in only AA without T2D. Among individuals with T2D, serum 25(OH)D concentrations were marginally associated with IL-6 (R2 = 0.109, B = 0.076, P = 0.085) in HA with T2D, and there was a trend toward significance with log leptin (R2 = 0.393, B = − 0.006, P = 0.075) in AA with T2D in regression analysis. Conclusions The findings that the associations of serum 25(OH)D concentrations with adipokines and cardiometabolic factors differ between HA and AA has clinical and public implications to guide design of T2D preventive strategies that are culturally specific even within the same ethnicity