IgG index and not serum 25-hydroxyvitamin D is associated with age at onset of multiple sclerosis

Background Vitamin D deficiency is associated with an increased risk of multiple sclerosis (MS). However, its effect on the age of disease onset remains unclear. This study examines the relationship between serum 25 hydroxyvitamin D (25(OH)D) levels and age of first symptom onset among recently diagnosed MS patients. Method Serum 25(OH)D was measured from forty MS patients sampled near disease onset. After correcting seasonal variability, a multivariable linear regression was used to examine associations to age at onset. Results Serum 25(OH)D was not correlated with age at onset (P>0.5). However, CSF IgG index was lower among patients with later disease onset (β=-5.35, P=0.028). Furthermore, we observed bias resulting from non-random distribution of sampling by season, which after correcting indicates a higher 25(OH)D level among patients sampled at relapse compared to remission, instead of lower as previously reported. Conclusion In summary, serum 25(OH)D was not associated with the age at onset.