Study Population
The case group consisted of adult patients with VVS aged 18 to 70 years.
These patients received this diagnosis after a comprehensive history
taking, physical examination, and guideline-indicated diagnostic
workups,1, 2 including electrocardiogram,
echocardiogram, electrocardiogram Holter monitoring, and laboratory data
in the syncope unit.25 The control group comprised
age- and sex-matched individuals without any history of syncope from
TeCS. The exclusion criteria were: 1) Taking midodrine or
fludrocortisone; 2) Taking oral or parenteral vitamin B supplements,
including but not restricted to folic acid, vitamin B12, vitamin B
complex, or hair supplements in the last six months; 3) Gastric,
intestinal, or bariatric surgeries; 4) Alcohol use disorder; 5) Taking
antiepileptic medications interfering with vitamin B12 or folate
metabolism, including phenytoin, phenobarbital, or carbamazepine; 6)
Taking methotrexate or isoniazid; 7) History of malabsorption, including
celiac disease, Crohn’s disease, or ulcerative colitis; and 8) History
of malignancy.