In a review article published May 2014 as part of a special issue of the journal Nutrients entitled “Vegan diets and Human health”, authors Fumio Watanabe, Yukinori Yabuta, Tomohiro Bito and Fei Teng examined Vitamin B12-containing plant food sources for vegetarians.
Through a comparison of plant-based foods, they sought to determine the best source of naturally occurring vitamin B12. Included in the review were various kinds of beans, leafy greens, other vegetables, mushrooms, and algae. They also discuss milk and egg yolks, finding the former to be very low in B12 and the latter to offer poor bioavailability of the vitamin.
After considering factors such as the concentration, consistency, and type(s) of B12 compounds, gastrointestinal absorption, and the presence of pseudovitamin B12 (as in spirulina), they declared a clear winner:
A survey of naturally occurring and high Vitamin B12-containing plant-derived food sources showed that nori, which is formed into a sheet and dried, is the most suitable Vitamin B12 source for vegetarians presently available. Consumption of approximately 4 g of dried purple laver (Vitamin B12 content: 77.6 µg /100 g dry weight) supplies the RDA of 2.4 µg/day.
Watanabe F, Yabuta Y, Bito T, Teng F. Vitamin B12-Containing Plant Food Sources for Vegetarians. Nutrients. 2014; 6(5):1861-1873.
In addition to being a great source of vitamin B12, nori contains iron and n-3 polyunsaturated fatty acids.
The authors concluded the impressive results for shiitake mushrooms in the iron department and for vitamin D2 (ergocalciferol), which they write are “also nutrients that vegetarian diets tend to lack.”