Folic acid (vitamin B9) and vitamin B-12
Another pairing that simply does not work, is folic acid and vitamin B-12. According to Dobrynina, is you take too much vitamin B9 and B12 (folic acid and folate), you will no longer be able to identify a potential vitamin B-12 deficiency.
According to various studies, among which one study published in the Cochrane Database of Systematic Reviews, in rare cases, excess consumption of these two vitamins can even lead to neurological problems. Vitamin B12 deficiency causes an anemia which has similar symptoms with the anemia caused by folate deficiency. Unlike folate anemia, b12 anemia can also cause serious problems to the central and peripheral nervous systems. Taking folic acid will help with the vitamin B12 deficiency but the risk of neurological problems will still exist, according to researchers.