WHY FOLIC ACID?
Folic acid works to prevent these birth defects only if taken before pregnancy and in the first few weeks of pregnancy. Since NTDs originate in the first month of pregnancy, before many women know they are pregnant, it is important for a woman to have enough folic acid in her system before conception. Folic acid is recommended for all women of childbearing age because 50 percent of pregnancies in this country are unplanned.
Studies show that, if all women consumed the recommended amount of this vitamin, beginning before conception and continuing into the first month of pregnancy, up to 70 percent of all NTDs could be prevented.
The neural tube is
the embryonic structure that develops into the brain and spinal cord.
This structure, which starts out as a tiny ribbon of tissue, normally
folds inward to form a tube by the 28th day after conception. When this
process goes awry and the neural tube does not close completely, defects
in the brain and spinal cord can result. About 2,500 babies are born with
NTDs each year, and many other affected pregnancies end in miscarriage
The most common NTDs are spina bifida and anencephaly. Spina bifida, often called open spine, affects the backbone and, sometimes, the spinal cord. Children with
the severe form of
spina bifida have some degree of leg paralysis and bladder and bowel control
problems. Anencephaly is a fatal condition in which a baby is born with
a severely underdeveloped brain and skull.
Studies also suggest that folic acid may help prevent some other birth defects as well, including cleft lip and palate. top
The Centers for Disease Control (CDC) recommends that all women who can become pregnant take a multivitamin that contains 400 micrograms of folic acid every day and eat a healthy diet. This is the only sure way a woman can get all the folic acid and other vitamins she needs. Most women get less than half of the recommended amount of folic acid daily.
The Institute of Medicine also recommends that women eat a diet rich in foods that contain folate or folic acid. Folate is the natural form of folic acid that is found in foods. Orange juice, other citrus fruits and juices, leafy green vegetables, beans, peanuts, broccoli, asparagus, peas, lentils and whole grain products all contain folate. Synthetic (manufactured) folic acid is added to certain grain products, including flour, rice, pasta, cornmeal, bread and cereals. These foods are considered "fortified" with folic acid.
The body more readily absorbs folic acid from vitamin supplements and fortified foods than folate from food. It is estimated that 50 percent of food folate is absorbed by the body, while approximately 85 percent of folic acid in fortified foods and 100 percent of the folic acid in a vitamin supplement are absorbed. Cooking and storage also destroy some of the folate in foods. The body cannot distinguish the origin of the vitamin, however; once in the bloodstream the biological function is the same.
Numerous studies have
shown that the synthetic form of folic acid helps prevent NTDs.
This is why the March of Dimes, the Centers for Disease Control and Prevention
(CDC), and the Institute of Medicine recommend that women who could become
Women need to get
enough folic acid every day throughout their reproductive years. To prevent
a woman must take folic acid daily at least one month before she conceives
and continue taking it through the first trimester (three months) of pregnancy.
All women capable of becoming pregnant-not just those planning a pregnancy-
should consume enough folic acid every day, because half of all the pregnancies
in the United States are unplanned. Remember, NTDs occur before many women
know that they are pregnant. top
How folic acid prevents NTDs is not well understood. Most studies suggest that it may correct a nutritional deficiency, while others suggest that supplemental folic acid helps some people compensate for inborn errors in how the body processes folates.
For example, a 1997 study found that as many as one in seven people may carry a genetic mutation (change) that causes them to have a deficiency in folic acid, even if they are consuming a diet that contains the recommended amount of folates. These people have problems breaking down folates found in food to forms of folic acid the body can use, resulting in lower folic acid levels in the blood. Most mothers of babies with NTDs don't have this gene mutation, but studies suggest that women who do may be at increased risk of having a baby with an NTD. However, taking folic acid raises levels of the vitamin in the blood, which can reduce the risk of having an affected baby. A new study also suggests that women with this mutation may have an increased risk of placental problems, such as placental abruption (when the placenta peels away from the wall of the uterus before delivery). This risk may be reduced by taking folic acid throughout pregnancy.
Besides helping to prevent certain birth defects, folic acid plays other important roles during pregnancy. A pregnant woman needs extra folic acid to help her to produce the additional blood cells she needs. Folic acid also is crucial to support the rapid growth of the placenta and fetus. This vitamin is needed to produce new DNA (genetic material) as cells multiply. Without adequate amounts of folic acid, cell division could be impaired, possibly leading to poor growth in the fetus or placenta. One study found that women who were deficient in folic acid were more likely to have a baby who was premature and of low birthweight (less than 5-1/2 pounds).
Another recent study
found that low levels of folate may be a risk factor for repeated early
There are several different types of NTDs. Spina bifida and anencephaly comprise 90% of all NTDs that occur. Encephalocele accounts for the remaining 10%. It is estimated that 4,000 pregnancies in the United States each year are affected by NTDs. Of that number, approximately 2,500 infants with NTDs are born.
When the upper end of the neural tube fails to close properly, early in the first month of pregnancy, two different types of NTDs can result: anencephaly and encephalocele.
When the lower end
of the neural tube fails to close properly, also during the first month
of pregnancy, spina bifida results. Meningocele, and myelomeningocele
are types of spina bifida.
Note: A third type of spina bifida is spina bifida occulta which consists of a small gap in the backbone or spine but no protrusion of the spinal cord or meninges (membranes that cover the spinal cord and the brain). Ordinarily, treatment is not needed, because there are usually no symptoms or disability. In fact, most people are unaware that they have this minor defect of the spine. top
Women should be aware that there are certain tests to indicate if a fetus has been affected by an NTD. When the neural tube fails to close, a fetal substance, AFP (alpha-fetaprotein), leaks into the amniotic fluid (fluid in the mother's uterus) and the mother's blood. Between the 16th and 18th week after a woman's last period, a test of a mother's blood revealing a high AFP level is an indicator that a pregnancy possibly is affected by an NTD.
If the blood test
reveals a high levels of AFP, the woman is encouraged to have an ultrasound
and possibly an amniocentesis. The ultrasound can be effective in diagnosing
all three types of NTDs. Ultrasound is used also before the amniocentesis
to identify where the placenta is located in the mother's uterus . Locating
the placenta reduces the risk of harm to the fetus during the amniocentesis.
During an amniocentesis, amniotic fluid is taken from the mother's uterus
with a long needle. This fluid is then tested for AFP levels. The results
of this test along with an extensive ultrasound examination are used to
confirm NTD-affected pregnancies. Women should be aware that these tests
cannot detect all NTDs and that there are sometimes "false positives"
associated with maternal blood serum AFPs. top
Historically, in the United States, NTD rates have been higher in East, particularly in the Appalachian region, than in the West. Similar geographic-based NTD rate variations have been observed in other countries also. Why these variations occur is not known but may be due to socio-economic levels, race/ethnicity, or other factors. top
NTDs occasionally result from chromosomal abnormalities or genetic traits. Also, it is plausible that many NTDs have a genetic component. NTDs are more likely to recur in families that already have an affected child, and they are more likely to occur in some racial/ethnic groups than others. Folic acid may work by correcting a folate deficiency or by overriding an inherited disorder of folate metabolism. It is known that 50-70% of NTDs can be prevented through the consumption of 400 micrograms of folic acid per day. top
The CDC guideline published in August 1991 and the PHS guideline published in September 1992 recommend that women who have had a previous NTD-affected pregnancy consume 400 micrograms (0.4 milligram) of folic acid daily if they are not planning a pregnancy and 4,000 micrograms (4.0 milligrams) of folic acid daily under the direction of their health care provider if they are planning a pregnancy.
More studies of the prevention of NTDs among other higher risk women need to be done. Nevertheless, these women should follow the PHS recommendation of 400 micrograms (0.4 milligram) of folic acid daily throughout their childbearing years. If they are planning a pregnancy, it is advisable for them to discuss their potential risk for having an affected child with their physician. They should talk about the advantages and disadvantages of using 4,000 micrograms (4 milligrams) periconceptionally (that is, one month before conceiving a baby through the first three months of pregnancy). Other high-risk women include:
The average total lifetime cost to society for each infant born with spina bifida is approximately $532,000 per child. This estimate is only an average. For many children, the total cost may be well above $1,000,000. The money involved does not address the physical and emotional tolls upon the families affected. top
Although not conclusive, there is some evidence that periconceptional use of folic acid may prevent other types of birth defects. These include cleft lip and cleft palate as well as some congenital heart defects, limb-reduction defects, and urinary tract defects.
High levels of the amino acid homocysteine are independently associated with an increased risk for heart disease and stroke. Studies have shown that taking folic acid lowers homocysteine levels in both men and women, but it has not been proven yet that folic acid supplementation lowers the risk for heart disease and stroke.
Folic acid may play
a role in prevention of cancers of the cervix and colon and lung, but
more study is needed. top
The FDA had allowed for additional amounts of folic acid (beyond the level of 140 milligrams per 100 grams) to be added to individual enriched cereal-grain products whose levels of folic acid may be lost due to factors such as food preparation and product shelf life. Thus, depending on the type of food and the estimated loss of folic acid due to many factors, different amounts of folic acid are added to enriched cereal-grain products to ensure that 140 micrograms of folic acid will be consumed per 100 grams of enriched cereal-grain product. top
*Source: Preventing Neural Tube birth Defects: A Prevention Model and Resource Guide. CDC 2002.