Complex sentence: Spirulina does not contain vitamin B 12 naturally (see table), and spirulina supplements are not considered to be a reliable source of vitamin B 12, as they contain predominantly pseudovitamin B 12, which is biologically inactive in humans.
Split into simpler sentences: Spirulina does not contain vitamin B 12 naturally (table) and is not considered to be a reliable source of vitamin B 12 added to spirulina supplements. Spirulina supplements contain predominantly pseudovitamin B 12, which is biologically inactive in humans.