Online Supplemental Material Assessed for eligibility via online questionnaire (n = 2010) Excluded for at least one exclusion criteria (n = 1887)   Analyzed at baseline (n = 34) Analyzed at 12 weeks (n = 30) Analyzed at baseline (n = 42) Analyzed at 12 weeks (n = 36)   Fulfilled the study criteria and invited (n = 123) Refused to participate (n = 24)   Did not attend visit I (n = 23, 9 placebo, 14 vitamin) Visit II (12 weeks) - Completed the study (n = 30) - Did not return for visit II (n = 4) - Completed the study (n = 36) - Did not return for visit II (n = 6) Attended visit I (baseline), n = 34 Blood collected, received the placebo toothpaste Attended visit I (baseline), n = 42 Blood collected, received the toothpaste with 100 µg cyanocobalamin / g Agreed and randomized (n = 99) 48 placebo, 51 vitamin Supplemental Figure 1. Study flow diagram.

Online Supplemental Material Supplemental Figure 2. Directed Acyclic Graph showing potential factors affecting the outcome of the study. The exposure is ‘treatment allocation’ and the outcome is ‘changes of B-12 markers’. The following assumptions were made: I)- vitamin use could be a confounding factor for the allocation to B-12 or placebo; II)- vitamin use prior to the study could have affected baseline vitamin B-12 markers; III)- baseline vitamin B-12 markers could have affected the outcome (response of vitamin B-12 markers to treatment). Therefore, baseline levels (or vitamin usage) could bias the causal effect of the exposure on the outcome. Adjusting for baseline vitamin B-12 markers (or for vitamin usage) is judged as necessary to proof a causal effect of vitamin B-12 supplementation on changes of the blood markers.

[supplement non-user] Online Supplemental Material Mean, 95% CI 90 70 50 30 10 -10 -0.1 -0.9 2.0 53.2 21.0 -5.0 Delta holoTC, pmol/L Delta tHcy, µmol/L 300 100 -100 -300 -500 -700 -288 -146 -36 232 -27 Delta MMA, nmol/L Delta vitamin B-12, pmol/L Placebo arm N = 30 B-12 arm [supplement user] [supplement non-user] N = 6 * Supplemental Figure 3. Mean (95% confidence intervals, CI) of changes of the 4 vitamin B-12 biomarkers according to background supplement usage in the active treatment arm. Thirty vegans (from the 36 who completed the intervention) reported vitamin B-12 supplementation prior to and during the study. Vegans who received the placebo were considered as one group. Mean values for the changes are shown. The changes (delta) were calculated as levels at 12 weeks minus those at baseline. * p values < 0.05 for the comparison of the changes in the subgroups with those in the placebo arm according to general linear model univariate analysis of variance test. HoloTC, holotranscobalamin; MMA, methylmalonic acid (shown here in nmol/L); tHcy, total homocysteine.

Online Supplemental Material Supplemental Figure 4. The correlation between combined B-12 indicators (cB-12) at baseline and post intervention with placebo or vitamin B-12 fortified toothpaste in the 66 vegan subjects who completed the 12 weeks intervention. cB-12 was calculated from 4 markers (holoTC, vitamin B-12, MMA, tHcy) and corrected for age according to Fedosov et al., (1). The correlation coefficients and p values between baseline and 12 weeks cB-12 values are according to Spearman test. cB-12 categories: probable vitamin B-12 deficiency (cB-12  -2.5); possible vitamin B-12 deficiency (cB-12 > -2.5 to -1.5); low vitamin B-12 (cB-12 > -1.5 to -0.5); vitamin B-12 adequacy (cB-12 > -0.5 to 1.5); elevated vitamin B-12 (cB-12 > 1.5). 2 1 -1 -2. -3 -4 -2 Placebo Vitamin B-12 4 markers cB-12 at baseline adjusted for age 4 markers cB-12 at 12 weeks adjusted for age R = 0.866, p < 0.001, n = 30 placebo arm R = 0.644, p = 0.005, n = 36 vitamin B-12 arm