Abstract
In previous work we identified a group of children (n = 48) between the ages of 10-18 years whose diagnostic workup for chronic nausea unexplained by conventional diagnostic tests revealed that 60% had underlying cardiovascular instability (n = 30) presenting as orthostatic intolerance (OI). The OI could be sub-classified based on head up tilt (HUT) testing into three groups: Postural Orthostatic Tachycardia Syndrome (POTS), orthostatic hypotension (OH) and syncope. Children with OI in all three groups had a greater reduction in autonomic control upon HUT manifested as greater loss of baroreflex sensitivity (BRS) and heart rate variability (HRV) and higher norepinephrine levels compared to those in the non OI group. Vitamin D deficiency is associated with impaired vascular responses to vasoconstrictors and alterations in autonomic control mechanisms in adults. In this study we sought to determine if vitamin D level is lower in these pediatric OI subjects and if it correlates with the hemodynamic responses to tilt. Serum 25(OH)D tended to be lower in OI vs non OI (18.6 ± 0.7 ng/ml, n = 25, vs 22.2 ± 2.4 ng/ml, n = 15; p = 0.16). Most importantly 25(OH)D showed a high positive correlation with supine measures of BRS (seq ALL, R = 0.51, p = 0.05), HRV (rMSSD, R = 0.44, p = 0.02) only in the OI group and there was a trend for a negative correlation with sympathovagal balance ( LF/HF ratio: R =-0.35, p = 0.08). Low 25(OH)D correlated with greater loss of both BRS (R = 0.51, p = 0.01) and HRV (R = 0.44, p = 0.05) upon HUT. These findings support the concept that low vitamin D may contribute to impaired responses to tilt in OI subjects. Further work is needed to evaluate if vitamin D supplementation will improve the vascular and hemodynamic responses to tilt and help improve the OI symptoms. Our goal is to provide a safer therapeutic alternative for the treatment of OI in children.
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