The Scientific Evidence: Nori's Bioavailable B12
For years, there has been confusion within the plant-based community regarding seaweed as a source of vitamin B12. This stemmed from early studies that didn't differentiate between various types of algae, some of which contain inactive 'pseudo-vitamin B12'. However, recent and more rigorous research has specifically focused on nori (purple laver) and provided definitive answers. A notable 2024 randomized controlled trial investigated the bioavailability of vitamin B12 from nori in vegetarians. The study found that consuming just 5 grams of nori per day for four weeks led to a significant improvement in the participants' vitamin B12 status. This was measured using a panel of biomarkers, including holotranscobalamin (holoTC) and homocysteine (Hcy), which are reliable indicators of active B12 levels in the body.
The key takeaway from this research is that the vitamin B12 found in purple laver is not an analogue that blocks absorption but is instead the genuine, bioavailable form. The study's authors also noted that the improvement in B12 status was comparable to that seen with other reliable sources like fortified milk or supplements. This provides strong evidence that nori can be a legitimate component of a vegetarian or vegan's strategy for meeting their B12 needs, alongside fortified foods and supplements.
Nori vs. Spirulina and Other Algae
It is critical to distinguish nori from other algae, particularly spirulina, which is often mistakenly promoted as a reliable source of vitamin B12. The B12 compounds in many other sea vegetables and microalgae, including spirulina and some forms of chlorella, are largely inactive analogues. These pseudo-B12 compounds can interfere with the absorption and metabolism of true vitamin B12, potentially worsening a deficiency.
Here are some key differences between nori and spirulina:
- Bioavailability: Nori has been shown to contain biologically active and absorbable vitamin B12, as confirmed by human trials. In contrast, spirulina contains mostly pseudo-B12 that is not effective in humans.
- Impact on B12 status: Consuming nori has a beneficial effect on B12 status markers. Older studies that included spirulina showed worsened B12 status, likely due to the inactive analogues.
- Nutrient profile: While both are nutrient-dense, nori is rich in iodine and certain antioxidants, while spirulina is an excellent source of protein and other B vitamins but is unreliable for active B12.
Comparison Table: Nori vs. Spirulina
| Feature | Nori (Purple Laver) | Spirulina (Blue-Green Algae) |
|---|---|---|
| Primary Form of B12 | Contains biologically active vitamin B12 (true cobalamin). | Contains mostly inactive pseudo-vitamin B12 analogues. |
| Bioavailability in Humans | Proven to be bioavailable and improve B12 status in human trials. | Not bioavailable; may interfere with true B12 absorption. |
| Reliability for B12 | Considered a potential, though variable, dietary source. | Not a reliable source and should not be depended on for B12 needs. |
| Other Noteworthy Nutrients | Excellent source of iodine, antioxidants, and Omega-3s. | High in protein, iron, and several B vitamins (not B12). |
| Primary Use | Sushi wraps, snacks, garnish. | Powder supplements, tablets. |
How Much Nori is Needed for Your B12 Needs?
While nori contains bioavailable B12, it is not a consistently precise source. The B12 content can vary significantly depending on the variety, growing conditions, and processing. Some tests have shown roasted nori to contain between 23.1 and 52.8 µg per 100g. A study found that 5g per day provided 1.9 µg of B12, close to the Recommended Dietary Allowance (RDA) of 2.4 µg. However, relying solely on nori could lead to insufficient intake due to this variability and the risk of consumption fatigue. Therefore, nori is best considered as a helpful component of a varied diet, not as the sole B12 solution. Frequent consumption alongside fortified foods can enhance overall B12 intake.
Fortified Foods and Supplements: The Reliable B12 Strategy
For vegans and vegetarians, particularly those who have been on a restricted diet for a long time, relying on fortified foods and B12 supplements remains the most reliable strategy to avoid deficiency. The Vegan Society and other health organizations consistently emphasize this point.
Reliable Vegan B12 Sources:
- Fortified Plant Milks: Many soy, oat, and other plant-based milks are fortified with B12. Check the label for cyanocobalamin, the most common supplemental form.
- Fortified Cereals: A quick and easy way to add B12 to your morning routine. Again, check the nutrition label.
- Nutritional Yeast: This popular vegan condiment is often fortified and provides a cheesy, nutty flavor. A typical serving can provide over 100% of the daily value for B12.
- B12 Supplements: For many, especially those with poor absorption or low dietary intake, a daily or weekly supplement is the most reliable method.
Conclusion
In conclusion, yes, nori does contain bioavailable vitamin B12 that can be absorbed by the human body. Recent human research has confirmed its effectiveness in improving the B12 status of vegetarians. However, due to the natural variability of B12 content in nori, it should not be treated as the only source for individuals on plant-based diets, especially for long-term health. The most prudent approach is to include nori as a complementary source alongside reliable fortified foods and/or supplements to ensure adequate intake and prevent B12 deficiency. For more information on vegan nutrition, including B12, see the Vegan Society's Guide to B12.
