Why is Niacin the suggested solution if too much Active B12 with L-5-MTHF is taken?

Since each individual has different daily requirements for each vitamin and mineral depending on a number of factors such as diet, metabolism, medical conditions, genetics, size, age, etc., there is no one-size-fits-all dosage recommendation. Depending on these factors, it is possible to take too much of certain nutrients for your individual needs. Please see Dr. Lynch's article regarding Methylfolate Side Effects http://mthfr.net/methylfolate-side-effects/2012/03/01/ for more information.