Vitamin D status, body composition and glycemic control in Polish adolescents with type 1 diabetes

High prevalence of vitamin D deficiency in adolescents with type 1 diabetes (T1DM) has been recorded but data focused on the relationship between vitamin D, glycemic control and body composition is limited in T1DM patients. The study was aimed to investigate vitamin D status in T1DM patients and its association with body composition (fat and lean body mass) and clinical data.

The study group comprised of 100 adolescents (15.3±1.9 yrs; 54 girls), including 60 T1DM patients (15.1±1.9 yrs; 32 girls) and 40 controls (15.6±1.8 yrs; 20 girls) from Warsaw, Poland. Serum total 25-hydroxyvitamin D (25(OH)D) levels and iPTH were measured by an ECLIA (Roche Diagnostics). Glycosylated hemoglobin (% HbA1c), serum calcium and inorganic phosphorous, and the use of dietary supplements were also assessed. DXA (GE Prodigy) was used to assess lean body mass (LBM; g), fat mass (FM; g), FM/LBM ratio, and respective Z-scores.

Mean 25(OH)D level of 15.3±7.0 ng/mL (range 4.2-37.7 ng/mL) in T1DM was not different from that observed in controls (17.9±9.3 ng/mL; range 6.3-40.4 ng/mL). Eighty-two percent of T1DM patients and 67% controls had 25(OH)D levels <20 ng/mL, among them 25% T1DM and 12.5% controls revealed values <10 ng/mL. 5% T1DM and 15% controls had 25(OH)D>30 ng/mL. 25% from T1DM and 22% from control groups declared to use vitamin D supplementation and had significantly higher 25(OH)D levels compared to non-users (22.6±7.6 vs. 12.8±4.8 ng/mL in the T1DM; 26.9±11.5 vs. 15.3±6.8 ng/mL in controls, respectively). In the T1DM, low 25(OH)D levels negatively correlated with HbA1c (r=-0.320, P=0.013) and with iPTH (r=-0.434, P=0.001). 25(OH)D levels correlated negatively with Z-scores for FM/LBM ratio (r=-0.324; P=0.012) and Z-scores for FM (r=-0.229; P=0.079) and positively with LBM Z-scores (r=0.300; P=0.020). Serum Ca, serum iPTH did not differ T1DM and control groups but serum P level was significantly higher in T1DM patients compared to controls (1.39±0.19 mmol/L vs. 1.18±0.18 mmol/L; P=0.001, respectively).

In T1DM adolescents vitamin D deficiency coincided with poor glycemic control and disturbed body composition. 25(OH)D levels were positively related to muscle stores and negatively with fat stores. Therefore, to limit a risk of disease related clinical complications both disturbed body composition and vitamin D deficiency should be corrected by implementation of regular vitamin D supplementation and increased intake of vitamin D-rich foods, as well as increased outdoors activities.