Unmetabolized folic acid causes the same symptoms as MTHFR mutations. Cornet, Dominique et al. “High doses of folic acid induce a pseudo-methylenetetrahydrofolate syndrome.” SAGE open medical case reports vol. 7 2050313X19850435. 17 May. 2019, doi:10.1177/2050313X19850435
Excess unmetabolized folic acid can interfere with processes needed for normal use of folate. Henry, Curtis J et al. “Folate dietary insufficiency and folic acid supplementation similarly impair metabolism and compromise hematopoiesis.” Haematologica vol. 102,12 (2017): 1985-1994. doi:10.3324/haematol.2017.171074
Zinc interacts with folic acid in the intestines and lowers absorption. Southon, S. (1990), "ZINC, IRON AND FOLIC ACID", Nutrition & Food Science, Vol. 90 No. 5, pp. 2-3. https://doi.org/10.1108/eb059310
Effect of oral folic acid supplements on zinc, copper, and iron absorption and excretion. Milne DB, Canfield WK, Mahalko JR, Sandstead HH. Effect of oral folic acid supplements on zinc, copper, and iron absorption and excretion. Am J Clin Nutr. 1984 Apr;39(4):535-9. doi: 10.1093/ajcn/39.4.535. PMID: 6711464
Intestinal transport of zinc and folic acid: a mutual inhibitory effect. Ghishan FK, Said HM, Wilson PC, Murrell JE, Greene HL. Intestinal transport of zinc and folic acid: a mutual inhibitory effect. Am J Clin Nutr. 1986 Feb;43(2):258-62. doi: 10.1093/ajcn/43.2.258. PMID: 3946290.
Methylation balancing is unique to each person, but can be done through diet and lifestyle changes.