Effect of roasted purple laver (nori) on vitamin B12 nutritional status of vegetarians: a dose-response trial.

ABSTRACT

PURPOSE: To investigate the bioavailability of vitamin B12 from nori and to evaluate the required dosage for improving vitamin B12 nutritional status in vegetarians not using supplements. METHODS: The study design is an open-label, parallel, dose-response randomized controlled trial. Thirty vegetarians were assigned to control (no nori), low-dose (5 g nori, aiming to provide 2.4 µg vitamin B12 per day), or high-dose (8 g nori, aiming to provide 4 µg vitamin B12 per day) groups. The primary outcome was changes in vitamin B12 status as measured by serum vitamin B12, holotranscobalamin (holoTC), homocysteine (Hcy), and methylmalonic acid (MMA), and a combined score of these four markers (4cB12 score) during the four-week intervention. Dietary vitamin B12 intakes were assessed at baseline and end of the trial with a 17-item food frequency questionnaire designed for vitamin B12 assessment. General linear model was used to compare least square means of changes in each biomarker of vitamin B12 status, among the three groups, while adjusting for respective baseline biomarker. RESULTS: After adjusting for baseline status, nori consumption led to significant improvement in serum vitamin B12 (among-group P-value = 0.0029), holoTC (P = 0.0127), Hcy (P = 0.0225), and 4cB12 (P = 0.0094). Changes in MMA did not differ significantly across groups, but showed within-group pre-post improvement in the low-dose group (median [p25, p75] = -339 [-461, -198] nmol/L). Vitamin B12 status appeared to plateau at low dose (5 g of nori), which compared with control group, improved serum vitamin B12 (lease square mean [95% CI] = + 59 [25, 93] pmol/L, P = 0.0014); holoTC (+ 28.2 [10.1, 46.3] pmol/L, P = 0.0035); Hcy (-3.7 [-6.8, -0.6] µmol/L, p = 0.0226); and 4cB12 score (+ 0.67 [0.24, 1.09], p = 0.0036). High-dose resulted in similar improvements. There was no significant difference between low-dose and high-dose groups in all biomarkers of vitamin B12. CONCLUSIONS: Consuming 5 g of nori per day for 4 weeks significantly improved vitamin B12 status in vegetarians. A higher dose (8 g) may not confer additional benefits. CLINICAL TRIAL REGISTRATION ClinicalTrials.gov Identifier NCT05614960. Date of registration November 14th 2022.