FRIDAY, Sept. 14, 2007 (HealthDay News) -- Blood levels of folic acid have increased among American women since the federal government mandated folate fortification to prevent birth defects, but questions remain as to how much folate is enough -- or too much.
A new study by the U.S. Centers for Disease Control and Prevention (CDC) finds that the number of women of childbearing age who have low blood folate levels has plunged following a 1998 federal mandate to enrich bread and grains with added folate.
The rate of low blood folate among women has fallen from 21 percent in 1988-1994 (before the fortification program) to less than 1 percent in 2003-2004, six years after fortification began.
That should mean fewer birth defects tied to low maternal folic acid levels in pregnancy. These anomalies include serious neural tube defects such as spina bifida. According to the March of Dimes, about 3,000 pregnancies are afflicted with these defects each year.
"Clinical trials have shown that folic acid supplementation effectively reduces the number of neural tube defects," said the study's lead author Christine M. Pfeiffer, acting chief of the Nutritional Biomarkers Branch at the CDC.
Her team published its study in the September issue of the American Journal of Clinical Nutrition.
Data used in the study was taken from the National Health and Nutrition Examination Surveys for the years 1988 through to 2004.
According to the CDC analysis, folate levels have continued to rise since 1998, although there was a slight dip in women's folate concentrations between the 2001-2002 and 2003-2004 surveys. However, average blood levels were still well above federal goals for red blood cell folate for women aged 15-44, Pfeiffer said.
The recent small dip in women's folate levels may have stemmed from the surge in popularity for low-carbohydrate diets, which may have prompted many women to move away from (fortified) bread and baked goods, the researchers said. However, "the slight downward trend after fortification seems unlikely to be functionally important" in terms of mom and baby's health, the study authors added.
Their study also cites a "lack of data" on just how much folate is ideal to shield against neural tube defects, and how much is too much from a safety standpoint. Right now, experts recommend that young women in their childbearing years get about 400 micrograms per day of the nutrient, which is also found naturally in leafy green vegetables and citrus fruits.
The notion of an ideal folate dose remains controversial, said Dr. Michael Katz, senior vice-president for research and global programs at the March of Dimes. His organization, along with others, is advocating an increase in fortification levels.
According to Katz, there's been a decline in neural tube defects of about 45 percent in every country that has adopted a folic acid fortification program. That still falls well short of the 75 percent drop that experts had hoped to see, he said.
On the plus side, there's no danger of adverse effects from folate "at the levels currently used in the United States," Katz said.
"There has been absolutely no evidence that it has caused undesirable side effects," he said. "In areas where [fortification and consumption levels] are higher, such as Chile, the same obtains. So, we have absolutely no reason to believe that harm results."
Dr. Malika Shah, a neonatologist at Children's Memorial Hospital in Chicago, affirmed Katz's position, saying that women who have had one child with a neural tube defect now frequently are given "an incredible amount of folic acid, and we haven't seen any negative effects. It doesn't seem to have a downside."
One folate expert differed with those assessments, however. Initially, 4 milligrams daily was considered suitable, but a Hungarian study in the early 1990s found successful reductions in the occurrence of neural tube defects at a daily dose of only 0.8 milligrams, noted Dr. Tsunenobu Tamura, a professor of nutrition sciences at the University of Alabama, Birmingham.
"I don't think the 'more the better' idea is correct," he said. "We don't need to have more than enough. If we take too much, there is a kind of suggestive data trend in the research showing that we may promote cancer occurrence."
Tamura said the CDC study is an important step toward monitoring folic acid and the ongoing impact of the U.S. fortification program. But a systematic study is also required to identify any potential side effects, he said.
"We need to have monitoring of how much we are eating and whether there is any danger of giving too much folic acid to the general population," Tamura said. Factors such as how much enriched grain someone consumes and the use of supplements, such as power drinks that contain folic acid, can make a difference in levels, he believes.
The fortification program "is a great thing we've achieved, but we should be very careful," Tamura said.
Find out more about nutrition at the U.S. Centers for Disease Control and Prevention.