Yet another "too much isn't good for you" story - with particular relevance to anyone taking folic acid and (maybe) folates.
High folic acid intake in aged mice causes a lowered immune response
January 11, 2016
Tufts University, Health Sciences Campus
A study in aged mice shows that excess folic acid intake causes lowered immune function because important immune cells, called natural killer cells, are less effective. These results build upon the findings of a previous study in 2005 by the same lab that found that 78 percent of healthy postmenopausal women had unmetabolized folic acid in their blood plasma, which is indicative of excess folic acid intake.