TPO and hematocrit: In a study that involved 78 children (mean age: 12.0±2.8 years) with HT, 25(OH)D3 deficiency (5-14.9 ng/mL) and severe deficiency (<5 ng/mL) rates were higher than the control group (n=74) and an inverse correlation between vitamin D and anti-TPO levels were reported (20).