What are the B vitamin suggestions based on?

The MTHFR gene codes for a key enzyme in the utilisation of B vitamins - Methyltetrahydrofolatereductase. 

Genetic variations in the MTHFR gene code for different versions of this enzyme with different efficiencies in utilising B vitamins.

Individuals that produce the less efficient versions of this enzyme will need to take in higher levels of B vitamins (particularly B6, B12 and folate) in order to see positive health effects.