UCLA

Background: Obese individuals are at risk for iron deficiency due to both insufficient dietary iron intake and trapping of iron through an interleukin-6 (IL-6) dependent pathway. Vitamin D deficiency, which is also common in obese individuals, contributes to the pro-inflammatory state of obesity. Obese individuals are also at increased risk for insulin resistance, which may be worsened by iron and vitamin D deficiency.

Objective: To evaluate the associations of, and interaction between, iron and vitamin D with inflammation and insulin resistance.

Design/Methods: 19 obese (BMI Z-score  2.0) and 28 lean (BMI Z-score -2.0 to 1.0) subjects were recruited (mean age 14.5 years, SD 2.1 years) in a cross-sectional study. Fasting serum was analyzed for iron status [soluble transferrin receptor (sTfR)], IL-6, and 25-hydroxy vitamin D (25[OH]D). Insulin sensitivity (Si) was determined by frequently sampled intravenous glucose tolerance test (FSIGT.) Iron deficiency was defined as sTfR level>8.3 mg/L. Vitamin D deficiency was defined as 25(OH)D level<20 ng/mL. Linear regression was used to measure the associations of, and interaction between, 25(OH)D and sTfR with IL-6 and insulin sensitivity.

Results: The prevalence of vitamin D deficiency was 37% in obese vs. 10% in lean subjects. STfR was negatively associated with Si (p<0.01) and positively associated with IL-6 (p<0.0001). 25(OH)D trended toward a positive association with Si (p=0.08) and was negatively associated with IL-6 (p<0.01). There was no interaction between sTfR and 25(OH)D in the associations with either Si or IL-6.

Conclusions: Higher vitamin D levels and better iron status are associated with increased insulin sensitivity and decreased inflammation in our small cohort. Micronutrient modulation may have a future role in dietary interventions for the prevention of insulin resistance and complications of chronic inflammation.