WASHINGTON, Jan. 10 (Xinhua) -- Women who are planning or capable of pregnancy should take a daily supplement containing 0.4 to 0.8 mg of folic acid, an influential U.S. panel recommended Tuesday.

The critical period for supplementation starts at least one month before conception and continues through the first two to three months of pregnancy, the U.S. Preventive Services Task Force (USPSTF) said in its final recommendation.

The USPSTF, an independent panel of national medical experts, said it found "convincing evidence" that taking folic acid before and during pregnancy provides "substantial benefits" in reducing the risk of neural tube defects in the developing fetus.

"These supplements can be taken as a daily multivitamin, prenatal vitamin, or single tablet that has the recommended amount of folic acid," Alex Kemper, a member of the USPSTF, said in a statement.

Neural tube defects are major birth defects of the brain and spine that occur early in pregnancy due to improper closure of the embryonic neural tube.

The defects may lead to a range of disabilities or death, including anencephaly, a condition in which a baby is born without parts of the brain and skull, and spina bifida, which occurs when the spinal cord and the bones surrounding the spine do not form properly.

Folic acid is found naturally in many fruits and vegetables, such as leafy greens, broccoli, and orange juice.

Additionally, in the United States, many foods such as flour, cereals, and breads are fortified with folic acid.

Daily folic acid supplementation recommendation was first issued by the USPSTF in 2009 but the group said most women in the U.S. still do not consume adequate amounts of this important vitamin.

It cited data from 2003 to 2006 showing that 75 percent of nonpregnant women aged 15 to 44 do not receive the recommended daily intake of folic acid.