In the past, there have been several studies that showed that nori contains or may contain some real vitamin B12 (not inactive vitamin B12 analogues). However, so far, the argument - at least in Europe and North America - was that these amounts of B12 are likely very low, likely due to contamination, that eating nori probably does not improve vitamin B12 status (including a lowering of MMA levels), and that there has been no RCT to prove otherwise.
But now, there has been an RCT, and it shows that nori really does seem to contain real B12 and that ... it does seem to increase vitamin B12 status.
The study results - Huang et al. (2024) - were published in a well-respected journal (Eur J Nutr) by Dr. Chiu's working group from Taiwan. This working group has published many papers with studies of vegetarians and vegans in Taiwan.
The study participants were vegetarians, including a handful of vegans. The study results were not reported for vegans separately in the main manuscript. But I made these six figures based on the "vegans only" data, based on Supplementary material 3 and info provided by the corresponding author (I asked).
Note: The participants ate quite a lot of nori: 5 or 8 grams per day.
Note 2: Although nori has a relatively moderate iodine content, eaten a lot of nori means ingesting a lot of iodine. However, 5 or 8 grams of nori would typically still contain less than 600 µg of iodine, which is the tolerable upper intake level (TUIL) proposed in Europe (by EFSA) for adults. In the USA, the TUIL for iodine is 1,100 µg/day (for adults).
Please refer to the original paper for the full results, including all participants. I was just curious what the results would be if one only looks at the vegans.
- Control group: no nori
- Low-dose nori intervention group: 4 sheets of nori (5 g) per day = 1.9 µg vitamin B12 per day
- High-dose nori intervention group: 7 sheets of nori (8 g) per day = 3.1 µg vitamin B12 per day
Every grey box in the figures below represents one single participant.
Serum homocysteine (Hcy)
4c combined B12 score (inclduing the four B12 parameters above) [note: the commas on the X axis are European "decimal commas", and should be decimal points in English, like inside the grey boxes - I was to lazy to change it.]
Please refer to the original paper for more info.
Here are some excerpts from the Huang et al. 2024, however:
"During the pre-planning stage, four brands of commercially available unflavored roasted nori, and one fresh nori harvested from Penghu island near Taiwan were purchased and tested for vitamin B12 content, and all of them contained true vitamin B12 (rather than analogues), as detailed in Table S1. We chose one commercial brand with opaque packaging and containing the highest vitamin B12 (48.4 µg/100 g) for the intervention, as transparent packaging may expose nori to light and contribute to vitamin B12 photo-degradation. ............However, when we sampled the nori from the batch used for the actual trial, it contained a lower amount of vitamin B12 (38.6 µg/100 g). This value would actually change the estimated vitamin B12 content to 1.9 and 3.1 µg for 5 g and 8 g of nori, respectively. These values were used for actual computation when assessing vitamin B12 intakes from nori. We also sampled the same brand of nori at different time throughout the year (Table S2)............... Serum vitamin B12 and folate concentrations were analyzed using electrochemiluminescence immunoassay (Roche cobas e601). Hcy was analyzed using Chemiluminescent microparticle immuno assay (Abbott ARCHITECT 1L71/ABRL004/R4). The remaining blood samples (for MMA and holoTC) were centrifuged at 3000 rpm for 15 min at 4℃ shortly after collection, and stored at a -80℃ freezer for analysis of serum MMA and holoTC at the end of the trial. Serum MMA was analyzed by the Department of Chemistry, Fu Jen Catholic University (New Taipei City, Taiwan) using liquid chromatography with tandem mass spectrometry (LC–MS-MS) (Sigma-Aldrich M54058). Serum holoTC was analyzed using an ELISA kit (IBL-International) by Yi-Her Laboratory (Yilan, Taiwan). ...................... 15 main sources of vitamin B12 for vegetarians and vegans in Taiwan: milk, liquid yogurt, yogurt, cheese, eggs, nori, mushroom, kimchi, fermented tofu [these are also mentioned as potential B12 sources], and the six available brands of plant-milk that are fortified with vitamin B12. ........................All participants [i.e., not just the vegans] showed improvement in all four vitamin B12 biomarkers except one participant who experienced a slight increase in MMA; however, this participant had a very low MMA value to begin with, and that both pre- and post- MMA concentration (from 49 to 142 nmol/L) were well below the cut point for deficiency (> 271 nmol/L). The detailed changes of biomarkers for each individual could be found in Fig. S1. ..................The high-dose group generally showed similar trends of improvement, though statistically significant pre-post improvement was observed only in serum vitamin B12 (+ 62 [31, 76] pmol/L) and Hcy (-3.5 [-5.3, -0.7]). For all the vitamin B12 nutritional biomarkers, there were no significant differences between low-dose and high-dose groups. Both within-group and among-group changes in serum folate were insignificant, as shown in Fig. 3(f). ................................If nori contains substantial amount of harmful analogues as previously suggested [6], functional markers such as Hcy and MMA would have worsen[ed]. The lowering of Hcy was unlikely influenced by folate nutritional status as serum folate did not change........................Is nori a reliable food source of vitamin B12?
Most plant foods – tempeh or other fermented products, organic vegetables grown with manure fertilizers – are unreliable sources of vitamin B12, as their vitamin B12 contents depend on haphazard contamination or adventitious presences of vitamin B12-producing microbes. On the contrary, Takenaka et al.’s experiment showed that purple laver cultured aseptically (treated with antibiotics) in medium devoid of vitamin B12 contained 50 ± 2 µg of vitamin B12 per 100 g dried weight, suggesting that vitamin B12 in purple laver [nori] is not by contamination and that purple laver may be able to biosynthesize cobalamin [vitamin B12] from within [36].
One possible objection to recommending nori as a food source of vitamin B12 is the variability of vitamin B12 contents. We sampled and tested vitamin B12 contents of all major brands we could find and at six different times throughout the year and all of them appeared to contain substantial amount of vitamin B12. Even the sample with the lowest amount (23.1 µg/100 g), if consumed at 5 g/d, could provide about 1.2 µg (50% RDA). Other published data also consistently showed similar levels, ranging from 28.9 (seasoned and toasted) to 133.8 µg/100 g (dried purple laver) [[studies from Japan:] 15 [Koseki et al. 2023, published in a Frontiers journal], 28 [Miyamoto et al. 2009], 36 [Takenaka et al. 2003]]. Although more sampling and testing are always warranted, the consistency of the results suggests that nori is likely a reliable source of vitamin B12. Our study found that 5 g of nori per day improved vitamin B12 intakes (from a meagre 0.3 µg to 2.0 µg [83% RDA]) in vegetarians, accompanied by improvement in vitamin B12 biomarkers.
..........................................Besides nori, other promising sea vegetables, such as Wolffia globosa duckweed ["Pham", duckweed, a freshwater plant] [41] and Taiwanese laver (hong-mao tai) [42] have been shown to increase vitamin B12 biomarker in human and warrant more rigorous testing. ................... ................... at the time of this study, there were only very few foods fortified with vitamin B12 (only a few imported plant-based milks and none of the meat analogues) in Taiwan, that the chance of confounding by other fortified foods were low. In addition, we analyzed the vitamin B12 content in nori of major brands commercially available, and at different seasons throughout the year to evaluate the variation of vitamin B12 content in nori to support our understanding on the reliability and the generalizability of nori as a source of vitamin B12. ..........................." Huang et al. 2024