Maternal Nutrient Intakes and Risk of Orofacial Clefts.

Several lines of evidence support an association between maternal use of a vitamin supplement with folic acid in early pregnancy and a reduced risk for offspring with orofacial clefts. First, several studies have shown reductions in the occurrence of clefts in infants whose mothers took vitamin supplements containing folic acid, including the public health campaign conducted in China by the Centers for Disease Control and Prevention. Second, studies have also shown the association of folic acid with a reduction in the risk of cleft recurrence in a subsequent sibling. Third, mothers’ use of folic acid antagonist medications has been associated with an increased risk of delivering offspring with oral clefts. Fourth, biologic plausibility for a relation between folic acid and reduced risk for orofacial clefting is available from experimental studies.

The underlying process by which folic acid may alter risk of clefting in humans is unknown. Furthermore, a sizable proportion of risk reduction may be associated with dietary intake of folate and other nutrients. However, there is a paucity of information about dietary factors, including folate, as potential risks of orofacial clefts even though numerous nutritional factors could potentially contribute to their etiologies. Selected nutrients (including folate, niacin, thiamine, B6, B12, riboflavin, zinc, amino acids, and carbohydrates) are likely parameters on which to focus given the associations that have been observed between these factors and neural crest cell malformations, including orofacial clefts.

DISCUSSION

Our analyses investigated whether women's intake of selected nutrients in the periconceptional period, including folate, decreased or increased risks of CLP or CP. These data did not reveal reduced risks for either phenotype associated with maternal intake of vitamin supplements containing folic acid. Some evidence was observed for decreased risks associated with increasing intakes of total protein, alanine, choline, methionine, and cysteine. With respect to dietary intakes of micronutrients, most single micronutrients appeared to be associated with reduced risks of CLP in models that considered intake data in quartiles and did not adjust for other nutrients. However, only 2 nutrients, iron and riboflavin, were associated with reductions in CLP risk when adjusted for other nutrients. We did not observe strong evidence that dietary intake of any other nutrients, including folate, was associated with CLP risk. Increased dietary intake of folate, thiamine, and zinc did appear to be associated with decreased CP risk among women who did not use vitamin supplements. Analytic consideration of the potential confounding influences of maternal race/ethnicity, age, and education did not suggest alternative interpretations of the results.

The strengths of this study include its large size, its population-based ascertainment of cases and controls, its relatively short period for maternal recall between periconceptional event of interest and interview, and its geographically multicentered U.S. population base. Nevertheless, our study had some potentially important limitations. First, some of our analytic models included nutrients that were correlated; thus, precision of risk estimation was reduced in some circumstances. Second, the percentage of those eligible who participated was approximately 70%. Although this percentage is within the range of acceptability for epidemiologic studies, the effects on risk estimation from the nonparticipants is unknown.

Third, these data relied on a food frequency questionnaire to assess nutrient intake. Limitations of this type of instrument have been described. Although the instrument we used was not internally validated, validation studies have revealed that it provides reasonable estimates of usual dietary intake for diets consumed by women even in the distant past. Fourth, this study estimated risks for intake levels of nutrients and not tissue–dose levels. Given individual variation in gut absorption and maternal–fetal exchange, we do not know how well maternal intake approximates the level of a particular nutrient that reaches the developing fetus.

Our observations contribute to the limited body of evidence suggesting that a woman's periconceptional diet may influence risks of CLP or CP in her offspring. The absence of a protective effect of periconceptional use of supplements containing folic acid is inconsistent with many previous observations, but not all. The reason for this lack of an association is unknown. We speculated that the protection afforded by folic acid through supplements might no longer be operating because of higher dietary levels of folic acid from fortification of the U.S. food supply during the study time period. We explored this possibility by estimating risks associated with maternal supplement use among women whose dietary folate intake was within the lowest quartile of intake of all control mothers. The use of vitamin supplements did not reduce the risks among this subset of the study population. Furthermore, given that the lowest quartile cutoff of dietary folate intake was at a higher level than has been observed previously, we estimated risks specifically for maternal supplement use among women whose dietary folate intake was within the lowest decile of intake of all control mothers (data not shown). These stratified analyses also did not indicate reduced risks among the subset of the population whose dietary intake of folate was within the lowest decile.

Although supplemental folic acid intake has been the focus for many of the inquiries regarding the association of periconceptional nutrition with clefting, there have been a few observations made about other nutrients. In particular, investigators in The Netherlands have observed reduced risks of CLP associated with increased maternal dietary intakes of several B vitamins, including thiamine, niacin, and pyridoxine, and increased intakes of vegetable protein, fiber, beta-carotene, vitamin C, vitamin E, iron, and magnesium. These investigators observed lower serum zinc and serum vitamin B6 concentrations in mothers who previously delivered infants with CLP compared with mothers who delivered nonmalformed infants, but did not observe associations between CLP and mothers’ serum glucose or myoinositol levels. Munger et al, in a study conducted in the Philippines, also observed lower serum vitamin B6 levels and higher folate levels in mothers who had previously delivered infants with CLP.

The integration of current study data with the existing literature suggests that periconceptional intake of B vitamins, choline, protein/selected amino acids, and iron may contribute to reduced clefting risks. Moreover, risks associated with these nutrient intakes may vary depending on whether the phenotype is CLP or CP alone. Animal experiments support the role of B vitamins. For example, B vitamins, particularly B1, B2, and B6, given in high dosages can reduce the incidence of clefts in selected murine strains.

Conclusion:

Our observations contribute to the limited body of evidence suggesting a woman's periconceptional diet may influence clefting risks in her offspring. Our finding of no reduction in clefting risk with periconceptional use of supplements containing folic acid is inconsistent with many previous observations but not all.