Micronutrient Intake During Pregnancy: Effects of Excessive Folic Acid on Placental Health and Function

Abstract

Background: In addition to a diet including fortified dietary staples, the use of prenatal multivitamin supplements among women has been shown, in some cases, to lead to excessive micronutrient intake levels for nutrients such as folic acid (FA). It was therefore hypothesized that prenatal vitamin supplementation, in addition to a standard Canadian diet, would place pregnant Canadians at risk for excessive FA intake. With little available research on the potential negative impact of excess FA intake in pregnancy, it was further proposed that high concentrations of FA may adversely affect placental health and function. Thus, the aim of the current study was three-fold: 1) To determine micronutrient intake in a large Canadian cohort of pregnant women; 2) To determine the extent to which FA intake in this cohort may exceed the tolerable upper intake level (UL) after prenatal supplementation; and 3) To determine the effects of excessive FA exposure on placental health and function in vitro. Methodology: Second trimester 3-day food records of pregnant women (N=216) were analyzed for micronutrient intake using ESHA Food ProcessorTM. Nutrient intake values were compared to established Dietary Reference Intake (DRI) values. In a series of experiments, the effects of exogenous folic acid (2-4000 ng/ml) on placental health and function were examined in two placental cell lines [HTR-8/SVneo (N=3) and BeWo (N=3)], and a human placenta explant model (N=6). Following a 48-hour incubation period, the effects of excessive folic acid exposure on placenta cell proliferation, viability, and apoptosis were determined, along with evaluation of placenta cell function via cell invasion and B-hCG hormone release assays. Results: Through dietary sources alone, most pregnant women studied were consuming adequate levels of most micronutrients. However the majority of examined women (>50%) demonstrated a risk of dietary inadequacy for vitamin D, vitamin E, folate, and iron. In the examined cohort, 83% of study participants reported prenatal supplement usage. In vitro exposure of human placenta cells and explants to excessive FA concentrations resulted in no significant differences in cellular proliferation, apoptosis, invasion, or B-hCG hormone production. However, decreased cell viability was observed in BeWo cells at increased FA concentrations (200-2000 ng/mL). Conclusion: Food sources alone do not appear to provide women in Canada with adequate intake of all micronutrients recommended for a healthy pregnancy. Though a prenatal supplement containing FA may be necessary for most women, current FA levels in many prenatal supplements may lead to excessive FA intake above the established UL. Yet, as measured in this study, high FA concentrations do not seem to adversely affect most primary indicators of placental cell health or function.