Limitations
Our findings should be interpreted in the light of the following
limitations: 1) This is an observational case-control study with its
inherent drawbacks; however, we selected the control group from a
population-based cohort to minimize the risk of bias. 2) We excluded
more than two-thirds of our patients due to a history of taking vitamin
B supplements in the last six months, which might bias our findings;
nonetheless, more than half of the screened individuals from TeCS were
excluded for the same reason as well. This eye-catching use of
supplements may be attributed to the concurrency of the coronavirus
disease 2019 (COVID-19) pandemic and our study because the usage of
vitamin supplements dramatically increased during the
pandemic.34, 35 3) The sample size of this study is
small; nevertheless, it should be noted that the non-COVID-19 healthcare
utilization dropped by one-third during the pandemic, which
substantially limited the number of eligible participants for this
study.36 4) It is more sensitive to screen for vitamin
B12 or folate deficiency by measuring serum levels of methylmalonic acid
and homocysteine,37 while we did not measure
methylmalonic acid in this study.