DISCUSSION
In this case-control study from a tertiary referral hospital and a population-based cohort, we found no remarkable difference in vitamin B12 or folate deficiency, or their serum levels between adult patients with VVS and controls; nonetheless, patients with frequent VVS are more likely to have lower serum levels of vitamin B12 compared to patients with infrequent VVS. Moreover, the prevalence of vitamin B12 deficiency is possibly higher in patients with frequent VVS compared to patients with infrequent VVS, albeit statistically non-significant, may be of clinical significance.