叶酸在怀孕期间对胎儿发育有重要作用。
叶酸缺乏会造成胎儿神经系统发育缺陷，所以美国医学会提倡所有可能怀孕的妇女补充
叶酸。
叶酸基本上没有副作用，除非长期服用每天超过1000mcg.
所以即使没有怀孕，也应该吃叶酸。
下面摘自WebMed
Folic acid is LIKELY SAFE for most people when taken by mouth or injected
into the body. Most adults do not experience any side effects when used in
doses less than 1000 mcg daily.
Folic acid is POSSIBLY UNSAFE when taken by mouth in large doses, long-term.
High doses of folic acid might cause abdominal cramps, diarrhea, rash,
sleep disorders, irritability, confusion, nausea, stomach upset, behavior
changes, skin reactions, seizures, gas, excitability, and other side effects.
There is some concern that taking too much folic acid for a long period of
time might cause serious side effects. Some research suggests that taking
folic acid in doses of 800-1200 mcg might increase the risk of heart attack
in people who have heart problems. Other research suggests that taking these
high doses might also increase the risk of cancer such as lung or prostate
cancer.
Special Precautions & Warnings:
Pregnancy and breast-feeding: Folic acid is LIKELY SAFE when taken by mouth
appropriately during pregnancy and breast-feeing. Taking 300-400 mcg of
folic acid daily is commonly used during pregnancy to prevent birth defects.
Procedures to widen narrowed arteries (angioplasty): Using folic acid,
vitamin B6, and vitamin B12 intravenously (by IV) or by mouth might worsen
narrowed arteries. Folic acid should not be used by people recovering from
this procedure.
Cancer: Early research suggests that taking 800-1000 mcg of folic acid daily
might increase the risk of cancer. Until more is known, people with a
history of cancer should avoid high doses of folic acid.
Heart disease: Early research suggests that taking folic acid plus vitamin
B6 might increase the risk for heart attack in people with a history of
heart disease.
Anemia caused by vitamin B12 deficiency: Taking folic acid might mask anemia
caused by vitamin B12 deficiency and delay appropriate treatment.
Seizure disorder: Taking folic acid supplements might make seizures worse in
people with seizure disorders, particularly in high doses.
