We investigated whether intakes of nutrients, including folate, by women in
the periconceptional period were associated with risks of neural tube defe
ct (NTD)-affected pregnancies. Data were part of a case-control study of fe
tuses and infants with NTDs among 1989-1991 California births. We conducted
interviews with mothers of 409 NTD cases and 420 nonmalformed controls. Nu
trient intake for the 3 months before conception was derived from food freq
uency questionnaires and from questions to mothers about vitamin/mineral su
pplement use. We computed NTD risk for each nutrient controlling for the in
fluence of all other studied nutrients and for maternal education, race/eth
nicity, height, and prepregnancy weight. Most single nutrients reduced NTD
risks when intakes were considered in quartiles and unadjusted for other nu
trients. Some of the same nutrients, however, did not provide similar inter
pretations when we adjusted for other nutrients. Adjusted analyses revealed
decreased NTD risks with increased intakes of methionine, lutein, magnesiu
m, zinc, and thiamin for women who did not use vitamin supplements periconc
eptionally. We observed decreased NTD risks associated with increased intak
es of linoleic acid, cysteine, calcium, and zinc for women who used supplem
ents. We also observed increased NTD risks with increased intakes of oleic
acid. For users as well as nonusers of vitamin supplements, we observed red
uced risks with increased intakes of grains and dairy products. Chance was
a likely alternative explanation for many of the observed risk patterns.