Folate Levels Fall in Young U.S. Women

It's not clear why blood folate levels dropped in this decade, but there are several possible explanations, experts said.

Increasing obesity rates among young women may be a factor. Research has found obese people metabolize folate differently than thinner folk, and some doctors believe heavier women need more folic acid to prevent neural tube defects, Green said.

Diet trends may have been be another factor, said Dr. Joseph Mulinare, a CDC epidemiologist who was the study's lead author.

He noted that in 1998, the Food and Drug Administration began requiring that folic acid be added to breads, cereals and other products that use enriched flour. Whole-grain breads were not under that mandate because they already contain some folate.

Low-carb diets increased in popularity during the early 2000s. Women who avoided flour and bread products because of their carbohydrates may have also taken in less folic acid, Mulinare said.

Vitamins and supplements are the best way to get the recommended daily dose of 400 micrograms of folic acid. But only a third of women of child-bearing age take a folic acid-containing supplement every day, he said.

Eating certain foods also helps, especially breads, cereals and other products containing enriched flour.

While whole-grain breads contain natural folate, it's a smaller amount than the folic acid in enriched breads. So the popularity of whole-grain breads "may be a factor" in the drop in folate levels, Mulinare said.