 How
does research prevent birth defects? The story of a recent
protective factor—folic acid—illustrates the transition from
scientific discovery to clinical care and public health policy.
DEMOGRAPHICS GIVE FIRST CLUES
The story opened with the observation that neural tube defects—serious
brain and spine abnormalities—occurred more commonly
in low-income families. Suspecting nutritional factors might
be responsible—in particular, lack of fresh vegetables
that supply the B vitamin folic acid—British researchers
gave vitamins with folic acid to pregnant women who had prior
babies with these conditions. There was an 87% reduction in
recurrences.
PUZZLING RESULTS CLARIFIED
Scientists then turned their attention to first-time occurrences
of neural tube defects. Interview studies from 1988-1993 showed
convincing results: about a 50% risk reduction in North American
women who took multivitamins with folic acid near the time
they conceived. However, a study of California and Illinois
women showed no benefit.
In 1995, a definitive California Birth Defects Monitoring
Program study helped clarify these findings. While vitamin
supplementation did lower risk in some women, there was less
benefit in other groups—namely, well educated White women
and Latina mothers. Because these women make up much of California's
population, folic acid's effect was blurred.
BENEFIT SEEN IN OTHER CONDITIONS
Our studies looked beyond neural tube defects, discovering
that folic acid—containing multivitamins lowered risk
for oral clefts, limb defects and heart defects as well. These
findings have since been confirmed in studies of other populations.
CLINICAL RECOMMENDATIONS ADOPTED
In 1992, strong cumulative evidence prompted the US Public
Health Service to recommend that all women take 0.4 milligrams
of folic acid daily. Healthcare providers echoed this message
in clinical practice.
Despite widespread public education campaigns, however, surveys
found many women still didn't get enough folic acid. Dietary
sources alone are often inadequate. And about half of pregnancies
are unplanned, so many women wouldn't have taken supplements
around the time of conception, a critical period for fetal
development.
PUBLIC POLICY INFLUENCED
With strong backing from the March of Dimes
Foundation and the Centers for Disease Control, in 1998 the
federal government mandated fortification of flour and other
foods to bolster folic acid intake among all women of childbearing
age.
Growing knowledge about folic acid and its role in lowering
neural tube defects is likely to be one reason they
have declined in the US over the last decade.
|
