Low Free Vitamin D Linked With CVD Risk Markers in Youth

Low concentrations of free 25 hydroxyvitamin D and bioavailable vitamin D may be associated with lower insulin sensitivity, worse endothelial function, and worse inflammatory biomarkers in youth, according to a new study.

To assess the relationship between free 25 hydroxyvitamin D, bioavailable vitamin D, insulin sensitivity, and cardiovascular disease risk markers, the researchers conducted a cross-sectional study that included 79 adolescents (aged 15.4 ± 0.2 years). Of the participants, 18 had normal weight, 30 had overweight, and 31 had overweight and prediabetes.

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The researchers recorded the participants’ reactive hyperemia index, body composition, and insulin sensitivity; measured the participants’ 25 hydroxyvitamin D and vitamin D binding protein; and calculated the participants’ free 25 hydroxyvitamin D and bioavailable vitamin D levels.

The participants who were in the lowest tertile of free 25 hydroxyvitamin D (4.0 ± 0.2 pg/mL) had significantly higher percent body fat (37.8 ± 1.1) and high-sensitivity C-reactive protein (3.4 ± 0.6), and had significantly lower insulin sensitivity (4.4 ± 0.4 mg/kg fat-free mass/min per μu/mL) and reactive hyperemia index (1.42 ± 0.06) than the participants who were in the middle (7.5 ± 0.3 pg/mL) or highest (17.0 ± 2.1 pg/mL) tertiles of free 25 hydroxyvitamin D.

After adjusting for percent body fat, the relationship of free 25 hydroxyvitamin D to both reactive hyperemia index and insulin sensitivity did not remain significant.

According to the researchers, the relationships were similar for bioavailable vitamin D. 

“Youth with low free [25 hydroxyvitamin D] or [bioavailable vitamin D] concentrations have lower insulin sensitivity and worse endothelial function and inflammatory biomarkers compared with those with more sufficient [25 hydroxyvitamin D],” the researchers concluded. “However, the effects of vitamin D on these biomarkers may not be independent of the effect of adiposity.”

—Colleen Murphy

Reference:

Bacha F, Klinepeter Bartz S, Tomsa A, Sharma S. Free vitamin D: relationship to insulin sensitivity and vascular health in youth. J Pediatr. 2019;212:28-34.e2. doi:10.1016/j.jpeds.2019.04.057.