Folic acid dilemma: one vitamin may impair cognition if another is lacking.

The nutrient folic acid is generally good for brain health, but research now suggests that too much of it might harm people who get too little vitamin [B.sub.12]. Those potentially at risk include vegetarians, whose diets may contain insufficient [B.sub.12], and elderly people, who tend to absorb the vitamin inefficiently.

Intake of folic acid, or folate, is higher in the United States than in most countries in part because U.S. food manufacturers have been legally obligated since 1998 to add it to grain products, such as baked goods and breakfast cereals.

The fortification policy exists because folic acid, when consumed by women around the time they conceive, prevents serious congenital malformations called neural tube defects. Moreover, studies suggest that folic acid can safeguard neurological health in older people.

Nevertheless, some researchers are concerned that exposing the entire population to supplemental folic acid may have unintended consequences. For instance, excess folic acid can mask signs of vitamin [B.sub.12] deficiency, including anemia. [B.sub.12] deficiency can cause irreversible neurological damage.

Some researchers also speculate that excess folic acid might directly harm the nervous system. A new study of more than 1,300 people age 60 and older supports that concern.

Epidemiologist Martha Savaria Morris and her colleagues at Tufts University in Boston used data from a national survey that had measured each volunteer's cognitive performance, anemia status, and blood concentrations of folic acid and vitamin [B.sub.12], among other parameters.

About 23 percent of the volunteers had [B.sub.12] concentrations that the researchers deemed low. Within that group, people who had the highest concentrations of folic acid were 9.6 times as likely to show signs of cognitive impairment as those with less folic acid. Surprisingly, anemia was also 3.1 times as common in the group with high concentrations of folic acid.

Among people with healthy [B.sub.12] levels, however, folic acid appeared to protect against cognitive impairment, and it had no significant relationship to anemia, the researchers report in the January American Journal of Clinical Nutrition.

"We only found potential adverse effects in people who had low vitamin [B.sub.12]," Morris says. "Generally speaking, folate is good for cognition."

Pharmacologist A. David Smith of the University of Oxford in England estimates that 1.8 million U.S. seniors may be at risk of anemia and cognitive impairment because of folic acid fortification. Governments in Europe and the United Kingdom have not mandated fortification, though British officials are considering it.

"I'm recommending to the U.K. government that they don't go ahead with fortification," says Smith. He also suggests that another form of folic acid might be safer.

Martha Clare Morris, an epidemiologist at Rush University Medical Center in Chicago, says she "agrees wholeheartedly" with Smith's assessment of folic acid's danger, and she laments the absence of a system for tracking potential side effects of the U.S. fortification policy. A 2005 Rush University study first linked intake of folic acid to cognitive decline in elderly people.

The apparent risks associated with excess folate may require a change in practice among U.S. physicians, says internist Jose Luchsinger of Columbia University. "In the era of folic acid supplementation, we may have to be more proactive at looking for [B.sub.12] deficiency in the elderly" he says.