The availability of vitamin B-12 from dried nori (Porphyra tenera) and spirulina (Spirulina sp.), was evaluated in rats.
Low serum, liver, and kidney cobalamin contents were measured after the depletion period using an Intrinsic Factor-based radioassay. However, no hematological abnormalities could be demonstrated in the B-12 depleted rats. After repletion, cobalamin contents of serum and kidney were significantly lower, and liver cobalamin content was higher, for both the nori- and spirulina-fed rats than for the cyanocobalamin-supplemented controls.
These data illustrate that cobalamins from algae are indeed absorbed by the rat.
In another study in 1991 though, other group of researchers found, and it cause a big confusion and uncountable misinterpretations over decades (till now, actually):
Although rising plasma vitamin B-12 concentrations in children consuming only plant foods (0.1-2.7 micrograms vitamin B-12/d) indicated that the vitamin B-12 was absorbed, elevated baseline values of (MCV) further deteriorated. In contrast, MCV improved in children receiving fish containing 0.15-0.5 microgram vitamin B-12/d or a vitamin B-12 supplement. Further studies on the specificity of current vitamin B-12 assays are warranted. It seems unjustified to advocate algae and other plant foods as a safe source of vitamin B-12 because its bioavailability is questionable.
An MCV blood test measures the average size of your red blood cells. Red blood cells move oxygen from your lungs to every cell in your body. If your red blood cells are too small or too large, it could be a sign of a blood disorder such as anemia, a vitamin deficiency, or other medical condition. - Dagnelie et al. (1991)
It was revisited in 2016:
Dagnelie et al. (1991) investigated how sea vegetables affected the hematological status of B12-deficient children and concluded that the algal-derived vitamin B12 was not bioaccessible to humans. However, their very small treatment group (n = 5) may have been insufficient to draw firm conclusions.
Takenaka et al. (2001) showed that feeding nori to vitamin B12-deficient rats yielded a 1.9-fold increase in hepatic levels of total B12 compared to those without nori supplementation.
Similarly, increased consumption of Chlorella or nori by vegan participants prevented B12 deficiency(Rauma et al. 1995).
(Helliwell et al. 2016) has established that the vast majority of cyanobacteria synthesize pseudocobalamin, but eukaryotic algae are dependent on B12 for growth. Therefore, sea vegetables are likely to be a more reliable source of the appropriate form of this vitamin.
Yamada et al. (1999) showed that air-drying asakusa-nori produced B12 analogs that are biologically inactive.
Takenaka et al. (2001): drying by lyophilization might have better nutritional outcomes.
Other factors of particular importance to preserving vitamin content include washing methods, storage temperature, light, and moisture content (Online Resource 1, Brown 1995; Jimenez-Escrig et al. 2001; Lage-Yusty et al. 2014).