微克。。。Overdose risks The risk of toxicity from folic acid is low, because folate is a water-soluble vitamin and is regularly removed from the body through urine.[62] The Institute of Medicine has established a tolerable upper intake level (UL) for folate of 1 mg for adult men and women, and a UL of 800 µg for pregnant and lactating (breast-feeding) women less than 18 years of age. Supplemental folic acid should not exceed the UL to prevent folic acid from masking symptoms of vitamin B12 deficiency.[63] There is growing concern worldwide that prenatal high folic acid in the presence of low vitamin b12 causes epigenetic changes in the unborn predisposing them to metabolic syndromes, central adiposity and adult diseases such as Type 2 diabetes. Another active area of research and concern is that excess folic acid in utero causes epigenetic changes to the brain leading to autism spectrum disorders.