Ulrich, C. M., & Potter, J. D. (2006). Folate supplementation: too much of a good thing?. Cancer Epidemiology Biomarkers & Prevention, 15(2), 189-193.
Henderson, A. M., Aleliunas, R. E., Loh, S. P., Khor, G. L., Harvey-Leeson, S., Glier, M. B., ... & Devlin, A. M. (2018). L-5-methyltetrahydrofolate supplementation increases blood folate concentrations to a greater extent than folic acid supplementation in Malaysian women. The Journal of nutrition, 148(6), 885-890.
Lamers, Y., Prinz-Langenohl, R., Moser, R., & Pietrzik, K. (2004). Supplementation with [6 S]-5-methyltetrahydrofolate or folic acid equally reduces plasma total homocysteine concentrations in healthy women. The American journal of clinical nutrition, 79(3), 473-478.