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.