Skip to main content
Public Health Nutrition logoLink to Public Health Nutrition
. 2016 Apr 18;19(14):2572–2579. doi: 10.1017/S1368980016000756

Serum and red-blood-cell folate demonstrate differential associations with BMI in pregnant women

Minxue Shen 1,2,3, Shazia Hira Chaudhry 2,3,4, Amanda J MacFarlane 5, Laura Gaudet 2,3, Graeme N Smith 6, Marc Rodger 3,4,7, Ruth Rennicks White 2,3, Mark C Walker 2,3, Shi Wu Wen 1,2,3,4,*
PMCID: PMC10270987  PMID: 27087411

Abstract

Objective

To examine the association between BMI and folate concentrations in serum and red blood cells (RBC) in pregnant women.

Design

A cross-sectional comparison of folate concentrations in serum and RBC sampled simultaneously from the same individual.

Setting

The Ottawa Hospital and Kingston General Hospital, Ontario, Canada.

Subjects

Pregnant women recruited between 12 and 20 weeks of gestation.

Results

A total of 869 pregnant women recruited from April 2008 to April 2009 were included in the final analysis. Serum folate was inversely associated and RBC folate positively associated with BMI, after adjusting for folic acid supplementation, age, gestational age at blood sample collection, race, maternal education, annual income, smoking and MTHFR 677C→T genotype. In stratified analyses, this differential association was significant in women with the MTHFR CC variant. In women with the CT and TT variants, the differential associations were in the same direction but not significant. Folic acid supplementation during pregnancy did not alter the differential association of BMI with serum and RBC folate concentration. This indicates that the current RBC folate cut-off approach for assessing risk of neural tube defects in obese women may be limited.

Conclusions

BMI is inversely associated with serum folate and positively associated with RBC folate in pregnant women, especially for those with the MTHFR CC variant.

Keywords: Obesity, BMI, Folate, Folic acid, Pregnancy


Folate status in women of childbearing age is important due to its role in the prevention of neural tube defects (NTD). Previous studies have observed a differential association between obesity and serum and red-blood-cell (RBC) folate concentrations in men, non-pregnant women of childbearing age and postmenopausal women( 1 5 ). Specifically, serum folate was found to be negatively associated, while RBC folate was positively associated, with BMI among non-pregnant adults( 1 5 ). The mechanisms for this differential association of obesity with serum and RBC folate concentrations are not clearly understood. Some investigators have suggested that the altered pharmacokinetics and distribution of folate in obese v. normal-weight persons may explain, at least in part, these differences( 6 , 7 ). It was observed that the peak serum folate concentrations of obese and normal-weight women were statistically different after a single oral dose of folic acid (0·4 mg), but there was no difference in overall area under the curve, indicating that obesity does not impair the absorption of folic acid but may lead to redistribution of folate from circulation into tissue. Folate requirements are higher in pregnancy in order to maintain placental and fetal growth, and accelerated folate catabolism and haemodilution during pregnancy can also result in decreased circulating folate concentrations( 8 10 ). Given the potential physiological and pharmacokinetic differences in pregnant v. non-pregnant populations, the association of obesity with serum and RBC folate concentrations may be altered. Owing to the observed differential associations of folate with BMI in previous studies, the standard RBC folate cut-off approach for assessing NTD risk in obese women may be limited. Lower serum folate in obese women may reflect a redistribution of folate in response to the higher mass of maternal tissue, potentially limiting the amount of folate available to the developing embryo which accesses folate through serum folate rather than RBC folate, thus increasing the risk of NTD. The identification of subgroups of women who may be susceptible to low folate status or respond differently to folic acid supplementation will ensure that public health interventions can be tailored to meet the needs of the entire population. We therefore examined the association of BMI with serum and RBC folate concentrations in pregnancy using data collected in the Ottawa and Kingston (OaK) Birth Cohort study( 11 ).

Method and materials

Data source

We used a subset of data from the OaK Birth Cohort, a prospective cohort study that recruited pregnant women at The Ottawa Hospital and Kingston General Hospital, Ontario, Canada, from September 2002 to April 2009. The subset included participants recruited from April 2008 to April 2009, from whom both serum and RBC folate were measured (Fig. 1). Participants were recruited between 12 and 20 gestational weeks and later delivered in the Ottawa–Carleton and Kingston regions. Participants were referred to the research team by clinic staff and asked to participate at their first antenatal visit. They were recruited into the study after information about the purpose of the study was provided and their written consent was obtained.

Fig. 1.

Fig. 1

Flowchart of participants, illustrating the procedure of study group identification (OaK, Ottawa and Kingston; GA, gestational age; RBC, red blood cells; MTHFR, methylenetetrahyrofolate reductase gene)

At the time of recruitment, participants’ self-reported demographic and lifestyle information including age, race, education, household income, folic acid supplementation and smoking. Nurses measured current height and weight at recruitment. Participants provided the brand name(s) of vitamin supplement(s) that were being consumed at the time of recruitment. Total daily supplemental folic acid intake was calculated based on the frequency of use and folic acid dose from all vitamin supplements. For women who were using more than one vitamin supplement, the total daily supplemental folic acid dose was calculated as the combined intake from all supplement sources.

Fasting blood samples were collected at the time of routine blood work, in order to avoid additional venepuncture. The blood samples were drawn from the antecubital vein or from the hand of the participating women at gestational age between 12 and 20 weeks, and measured in batches every month (i.e. the samples were stored for up to 1 month). Blood samples for serum folate testing were collected in serum separator tubes (Becton Dickinson, Franklin Lakes, NJ, USA) and allowed to clot. Samples were centrifuged for 10 min at 3000 g to separate serum. Serum was then removed and stored at −20°C until analysis. Folate concentrations were measured using the Beckman Coulter Access 2 and Unicel DxI 800 immunoassay analysers using the manufacturer’s reagents (Beckman Coulter, Brea, CA, USA).

Blood samples for measuring RBC folate concentration were collected in 3 ml purple-top EDTA tubes. Haematocrit was determined in fresh samples using an OSM3 hemoximeter (Radiometer, Copenhagen, Denmark). Samples were frozen at −20°C until analysis, at which point they were thawed and cells were lysed using Access RBC Folate Lysing Agent (Beckman Coulter). RBC folate concentrations were quantified using the Beckman Coulter UniCel DxI 800 Access Immunoassay System measured by competitive protein-binding assay. RBC folate concentrations were adjusted for haematocrit as described by the manufacturer.

Blood samples for genotyping the 677C→T polymorphism in the methylenetetrahyrofolate reductase gene (MTHFR) were collected in K2EDTA Vacutainer tubes. Samples were centrifuged at 1100 g and DNA was extracted using the BioRobot M48 and MagAttract DNA Blood Midi Kit (Qiagen, Hilden, Germany). PCR was used to amplify DNA regions of interest and genotyping was performed using the ABI 3130xl Genetic Analyzer and the ABI Prism SnaPshot Multiplex Kit (Applied Biosystems Inc., Foster City, CA, USA), which allows genotyping of several SNP in the same reaction( 12 ). The laboratory procedures for genotyping have been described previously( 11 , 13 ). For quality control, all assays were tested in hospital laboratories that are accredited by Ontario Laboratory Accreditation (OLA) and the Institute for Quality Management in Healthcare (IQMH), and are ISO certified for quality, competence and beyond.

Statistical analysis

Biomarker concentrations were non-normally distributed; therefore the geometric mean was used in our analysis. In regression analyses, logarithmic transformations were applied to variables with skewed distributions.

BMI was calculated and categorized into normal and underweight (<25·0 kg/m2), overweight (25·0–29·9 kg/m2) and obese (≥30·0 kg/m2). Underweight cases (n 41) were combined with normal-weight cases due to limited sample size. Use of folic acid supplements was categorized as: (i) no supplement; (ii) supplement with folic acid intake ≤1 mg/d; and (iii) supplement with folic acid intake >1 mg/d.

Characteristics of the participants were described and compared across BMI categories using χ 2 tests. ANCOVA was used to examine folate concentrations associated with participant characteristics, including BMI, daily folic acid supplement intake, MTHFR 677C→T genotype (CC, CT and TT), maternal age, gestational age at blood sample collection, race, maternal education, household annual income and smoking.

Multiple linear regression analysis was used to examine associations of folate concentrations with BMI, in all samples and in subgroups stratified by MTHFR 677C→T genotype or folic acid supplementation. Interaction between BMI and genotype was tested in the overall model. Supplementary analysis using the pre-gravid weight (self-reported) was also performed. The level of significance was set at 0·05. Statistical analyses were performed using the statistical software package SAS version 9.2.

Results

A total of 889 participants who had complete records for both serum and RBC folate concentrations were identified in the cohort. Seven participants reported the use of vitamin supplements but did not include information on dose, and thirteen women missed information on MTHFR 677C→T genotype, leaving 869 participants for the final analysis (Fig. 1).

The overall geometric mean concentration of serum folate was 45·7 (sd 18·7) nmol/l and the geometric mean concentration of RBC folate was 1549 (sd 378) nmol/l. Serum folate <7·0 nmol/l was non-existent, and only one participant’s serum folate was below 10 nmol/l. Demographic characteristics are shown in Table 1. Thirty-five participants (4 %) were not taking any vitamin supplements. The proportion of overweight and obesity were 26 % and 23 %, respectively. Twelve per cent of participants were homozygous for the MTHFR 677C→T variant (TT). Gestational age at recruitment, education, annual income, folic acid supplementation and MTHFR 677C→T genotype were statistically different among the BMI categories. Women with BMI ≥ 30·0 kg/m2 had a higher gestational age at recruitment, lower education, lower income, lower supplement use and were more likely to have the MTHFR CC variant.

Table 1.

Demographic characteristics of the study participants by BMI category: pregnant women (n 869) recruited between 12 and 20 weeks of gestation, Ottawa and Kingston (OaK) Birth Cohort study, April 2008–April 2009

BMI (kg/m2)
Overall <25·0 25·0–29·9 ≥30·0 P §
BMI (kg/m2) 869 100·0 446 51·3 226 26·0 197 22·7
Age (years)
≤29 420 48·3 223 50·0 107 47·3 90 45·7 0·181
30–34 293 33·7 145 32·5 70 31·0 78 39·6
≥35 156 18·0 78 17·5 49 21·7 29 14·7
GA at recruitment (week)
12 584 67·2 308 69·1 158 69·9 118 59·9 0·048
13–15 239 27·5 113 25·3 55 24·3 71 36·0
16–20 46 5·3 25 5·6 13 5·8 8 4·1
Maternal education
High school and below 170 19·6 91 20·4 34 15·0 45 22·8 0·010
College/university not completed 77 8·8 31 6·9 19 8·4 27 13·7
College/university completed 622 71·6 324 72·7 173 76·6 125 63·5
Race
Caucasian 796 91·6 400 89·7 211 93·4 185 93·9 0·111
Other races 73 8·4 46 10·3 15 6·6 12 6·1
Household annual income ($CAN)
Declined 46 5·3 31 6·9 6 2·6 9 4·6 0·005
≤49 999 244 28·1 128 28·7 54 23·9 62 31·5
50 000–79 999 274 31·5 123 27·6 77 34·1 74 37·5
≥80 000 305 35·1 164 36·8 89 39·4 52 26·4
Smoking
No 734 84·5 367 82·3 200 88·5 167 84·8 0·110
Yes 135 15·5 79 17·7 26 11·5 30 15·2
Folic acid supplement||
Non-users 35 4·0 10 2·2 9 4·0 16 8·1 0·009
≤1 mg/d 710 81·7 377 84·6 183 81·0 150 76·1
>1 mg/d 124 14·3 59 13·2 34 15·0 31 15·8
MTHFR 677C→T genotype
CC 371 42·7 181 40·6 90 39·8 100 50·8 0·036
CT 394 45·3 212 47·5 112 49·6 70 35·5
TT 104 12·0 53 11·9 24 10·6 27 13·7

GA, gestational age; MTHFR, methylenetetrahyrofolate reductase gene.

Data are presented as n and %. BMI = [weight (kg)]/[height (m)]2. BMI was measured in pregnancy (between 12 and 20 weeks of gestation); this may lead to misclassification of BMI category.

§

P value of χ 2 test.

||

Folic acid from supplements, not including folic acid from fortified foods or naturally occurring food folate.

Table 2 shows the determinants of serum and RBC folate concentrations. BMI showed an inverse association with serum folate but a positive association with RBC folate whether adjusted for or not (Table 2). Serum folate was lower with each additional variant allele such that CC > CT > TT; however, the trend was not statistically significant. Conversely, unadjusted and adjusted RBC folate was higher in participants homozygous for the T allele such that TT > CC and TT > CT. Folic acid supplementation was associated with higher serum and RBC folate concentrations. Gestational age at recruitment was a determinant of serum folate, and maternal age, gestational age at recruitment, education and smoking were determinants of RBC folate.

Table 2.

Geometric mean concentrations of serum and RBC folate by characteristics of participants: pregnant women (n 869) recruited between 12 and 20 weeks of gestation, Ottawa and Kingston (OaK) Birth Cohort study, April 2008–April 2009

Serum folate (nmol/l) RBC folate (nmol/l)
Unadjusted geometric mean 95 % CI Adjusted geometric mean 95 % CI Unadjusted geometric mean 95 % CI Adjusted geometric mean 95 % CI
Overall 45·7 44·1, 47·4 1549 1521, 1577
BMI (kg/m2)
<25·0 47·5 45·2, 50·0 47·4 45·2, 49·6 1500 1460, 1541 1503 1467, 1540
25·0–29·9 45·4 42·6, 48·3 45·0 42·2, 48·0 1549 1494, 1606 1532 1481, 1585
≥30·0 40·3 37·5, 43·3 41·0* 38·3, 44·0 1591 1527, 1657 1604* 1546, 1663
MTHFR 677C→T genotype
CC 46·4 44·0, 49·0 46·6 44·3, 49·0 1552 1504, 1602 1553 1513, 1594
CT 44·8 42·6, 47·0 44·3 42·2, 46·5 1471 1432, 1512 1473* 1436, 1510
TT 43·0 39·2, 47·3 44·1 40·1, 48·5 1712* 1629, 1799 1704*, 1622, 1790
Folic acid supplement
Non-users 24·1 21·8, 26·6 25·8 21·9, 30·5 1275 1155, 1409 1306 1197, 1426
≤1 mg/d 44·2* 42·9, 45·7 44·1* 42·6, 45·8 1512* 1485, 1540 1514* 1517, 1613
>1 mg/d 61·4*, 53·7, 70·3 61·0*, 55·9, 66·5 1743*, 1666, 1824 1722*, 1645, 1803
Age (years)
≤29 42·3 40·2, 44·4 43·4 41·3, 45·6 1430 1392, 1469 1470 1433, 1509
30–34 47·5* 44·8, 50·3 46·5 43·9, 49·3 1603* 1560, 1647 1564* 1517, 1613
≥35 49·7* 45·8, 53·9 48·0 44·4, 51·9 1700* 1633, 1771 1650* 1583, 1720
GA at recruitment (week)
12 45·9 44·1, 47·8 45·7 43·9, 47·5 1512 1478, 1546 1512 1481, 1544
13–15 44·9 41·8, 48·3 45·7 42·9, 48·6 1554 1498, 1611 1555 1504, 1607
16–20 39·2* 35·0, 43·8 38·0* 33·0, 43·8 1707* 1581, 1843 1693* 1571, 1825
Maternal education
High school and below 40·2 36·9, 43·7 42·1 38·6, 45·9 1327 1269, 1388 1408 1345, 1473
College/university not completed 42·6 38·1, 47·7 43·2 38·6, 48·4 1502* 1403, 1607 1496 1410, 1589
College/university completed 47·1* 45·2, 49·0 46·4 44·5, 48·4 1599* 1563, 1635 1574* 1540, 1608
Race
Caucasian 44·8 43·3, 46·5 44·9 43·4, 46·5 1531 1503, 1558 1532 1504, 1560
Other races 49·9 43·8, 56·9 49·0 43·6, 54·9 1559 1456, 1668 1545 1454, 1642
Household annual income ($CAN)
≤49 999 40·7 37·9, 43·8 43·2 40·1, 46·6 1375 1320, 1432 1490 1432, 1550
50 000–79 999 46·4* 43·7, 49·2 46·2 43·5, 49·0 1576* 1527, 1626 1544 1496, 1593
≥80 000 47·6* 44·9, 50·5 45·5 42·9, 48·4 1615* 1571, 1659 1540 1492, 1590
Declined 48·9 41·9, 57·0 49·3 42·7, 56·9 1645* 1537, 1760 1656 1535, 1786
Smoking
No 45·5 43·9, 47·1 45·1 43·5, 46·7 1569 1541, 1597 1553 1524, 1583
Yes 44·1 39·9, 48·7 46·2 42·3, 50·6 1352* 1280, 1427 1426* 1360, 1495

RBC, red blood cell; MTHFR, methylenetetrahyrofolate reductase gene; GA, gestational age.

*

Significantly different from the first category of the listed variables (P < 0·05).

Significantly different from the second category of the listed variables (P < 0·05).

Adjusted for all other variables listed.

Table 3 shows the association between BMI and serum or RBC folate, for all participants and in subgroups stratified by MTHFR 677C→T genotype or folic acid supplementation, adjusted for demographic variables. Overall, serum folate was inversely associated with BMI and RBC folate was positively associated with BMI. Interaction between BMI and genotype was not significant (P>0·05) in the overall model (data not shown). When stratified by MTHFR genotype, serum folate was inversely associated with BMI in women with CC and CT variants, while RBC folate was positively associated with BMI in women with the CC variant. In women with the TT variant, both associations were insignificant, but the direction remained consistent with that observed for the CC and CT variants.

Table 3.

Association of BMI with serum and RBC folate, stratified by MTHFR 677C→T genotype and folic acid supplementation; pregnant women (n 869) recruited between 12 and 20 weeks of gestation, Ottawa and Kingston (OaK) Birth Cohort study, April 2008–April 2009

Serum folate RBC folate
β 95 % CI P β 95 % CI P
All participants§ −0·32 −0·50, −0·16 <0·001 0·14 0·05, 0·22 0·001
MTHFR 677C→T genotype||
CC −0·42 −0·66, −0·17 <0·001 0·19 0·06, 0·32 0·003
CT −0·25 −0·49, −0·02 0·037 0·10 −0·02, 0·22 0·107
TT −0·16 −0·64, 0·32 0·521 0·10 −0·16, 0·36 0·449
Folic acid supplementation||
Non-users −0·62 −1·09, −0·14 0·011 0·44 −0·12, 1·00 0·124
≤1 mg/d −0·32 −0·48, −0·16 <0·001 0·12 0·02, 0·22 0·015
>1 mg/d −0·21 −0·78, 0·37 0·478 0·22 0·03, 0·41 0·021

RBC, red blood cell; MTHFR, methylenetetrahyrofolate reductase gene; β, the partial regression coefficient of log-transformed BMI.

BMI, serum folate and RBC folate concentrations were log-transformed.

§

Regression coefficient of BMI in all participants, adjusted for MTHFR 677C→T genotype, folic acid supplementation, age, gestational age at recruitment, race, maternal education, household annual income and smoking.

||

Regression coefficient of BMI in subgroups stratified by MTHFR 677C→T genotype or folic acid supplementation, adjusted for age, gestational age at recruitment, race, maternal education, household annual income and smoking.

Supplementary analysis using self-reported pre-gravid weight yielded similar results (data not shown).

Discussion

Our study confirmed a differential association of BMI with serum and RBC folate concentrations in pregnant women, such that BMI and serum folate concentration had an inverse relationship, and BMI and RBC folate concentration had a positive relationship. The differential associations were not significant in women with CT or TT genotype, although the direction of these associations was consistent in women with MTHFR CC genotype. Our data indicate that the differential association between serum and RBC folate and BMI observed in non-pregnant obese women likely persists into pregnancy. Serum folate was also found to be inversely associated with BMI at mid and late pregnancy in Korean women, although no RBC folate was measured simultaneously in that study( 14 ). In both Canadian and American populations, non-pregnant obese women, including those of childbearing age, have been shown to have lower plasma folate and higher RBC folate in comparison to normal-weight women( 2 , 5 , 7 ). These associations remained even after adjustment for dietary and supplemental folate intake, an important consideration given the observed pattern of lower folate intake among obese women( 2 , 5 ).

The associations were significant only for women with CC genotype and not significant for those with TT owing to limited sample size in the TT group, as well as increased measurement error attributed to the use of a competitive protein-binding assay to measure RBC folate, which is an important limitation of the present study. We observed a CC>CT > TT pattern in serum folate concentration, but a reversed TT>CC and TT>CT pattern for RBC folate concentration. In a meta-analysis, Tsang et al. reported a CC>CT>TT pattern in serum and RBC folate concentrations measured by microbiological assay, which was reversed for RBC folate concentrations measured by protein-binding assay( 15 ). The differences between the assays are due to differences in affinity of the assays for various folate forms. Plasma folates are exclusively monoglutamates and the majority are in the form of 5-methyltetrahydrofolate, whereas the majority of RBC folates are variable-length, long-chain polyglutamate 5-methyltetrahydrofolate. RBC folates must be hydrolysed into the monoglutamate form. The differences in affinities among these folate forms, as well as inconsistent proportion of folate forms among those with MTHFR 677C→T homozygous genotype (TT), impair the interpretation of RBC folate concentration measured by protein-binding assay( 16 ).

There are several other limitations to our study. First, the study design is cross-sectional, and serum and RBC folate were measured in early pregnancy; therefore, it is not possible to determine whether these associations hold through late pregnancy when haemodilution could have a significant effect. Second, the type and dose of supplements were self-reported and may be subject to measurement error due to inaccurate patient report and irregular pattern of use. We did not conduct dietary surveys on participants. Previous studies reported that obese women tended to under-report their food intake( 17 , 18 ), and folate from naturally occurring food sources exhibits variable and incomplete bioavailability, which can be affected by physiological conditions, pharmaceuticals and genetic polymorphisms( 19 21 ). Third, BMI was measured in early pregnancy (95 % were measured before 15 weeks) and this may lead to misclassification of obesity, although the weight gain in early second trimester is generally small( 22 ). Finally, samples were measured in batches and the storage time varied, but was no longer than 1 month. Serum folate stored in a frost-free freezer at −20°C for even a short period may be relatively unstable and sensitive to minor temperature fluctuations( 23 ). This may contribute to the variation in folate concentrations.

There are several strengths of the present study. First, to our knowledge, it is the first study to examine the association of obesity with serum and RBC folate concentrations in pregnant women. Because of the difference in folate metabolism between the non-pregnant and pregnant populations, it is important to examine if the observed differential association between obesity and folate concentrations measured from serum v. RBC would persist in a pregnant population( 1 5 ). Second, our study was based on data collected in a prospective cohort, which mitigates recall bias. Third, serum folate and RBC folate concentrations in our study were derived from the same fasted participants, thereby mitigating bias/confounding when examining the association between serum and RBC folate with BMI.

It is not clearly understood why obesity was inversely associated with serum folate concentration but positively associated with RBC folate concentration. Obese women may demonstrate lower serum folate concentrations due to volumetric dilution of the blood. Alternatively, higher RBC folate may be due to the redistribution of folate from circulation into tissues. Cell culture and animal studies have shown that the expression of tissue folate receptors and transporters is responsive to folate concentrations: folate deficient conditions induce the expression of reduced folate carrier in rat intestine and cultured human Caco2 cells( 24 , 25 ) whereas supplementation reduces its expression( 26 ). It could be hypothesized that the delay in absorption of folate observed in obese women may alter the expression of cellular folate transporters/receptors such that it promotes cellular uptake.

Folate status in women of childbearing age is important due to the role of folate in the prevention of NTD. The placenta takes up folate from the maternal plasma by the reduced folate carrier, the proton-coupled folate transporter and the folate receptor α( 27 , 28 ). Placental uptake of circulating folate ensures an adequate folate supply to the developing fetus. Obese women are at increased risk for NTD-affected pregnancy( 29 32 ). A proportion of the NTD risk associated with maternal obesity may be due to lower circulating folate in obese women, which can be corrected to some degree with higher folate intake( 29 ). On the other hand, it must be noted that a proportion of the NTD risk associated with obesity appears to be independent of folate status and may be due to other metabolic disturbances( 33 ). Obese women of childbearing age may therefore require supplemental folic acid to increase or maintain a plasma folate status that is associated with maximal protection from NTD. However, folate status associated with NTD protection is currently expressed in terms of RBC folate( 34 ). Because of the observed differential association of RBC folate with BMI, the standard RBC folate cut-off approach for assessing NTD risk in obese women may be limited. The relationship between RBC folate and serum folate, and how they relate to NTD risk reduction, may need to be determined for women of all BMI categories to determine appropriate ‘cut-offs’ for NTD protection.

A second consideration is whether obese women respond to folic acid supplementation similar to normal-weight women. Folic acid supplement use did not necessarily mitigate the observed differential association of BMI with serum and RBC folate in these pregnant women. A pharmacokinetic study found that obese women demonstrated a lower peak serum folate concentration after a 400 µg bolus folic acid dose and a lower area under the curve in the absorptive phase (0–3 h post-bolus), but no difference in the overall area under the curve( 7 ). The data indicate that obesity may delay the absorption of folic acid but that overall absorption is not impaired. It should be noted that the women in our study had a folate status associated with maximal protection from NTD risk (≥906 nmol/l)( 35 ). In our study, the overall mean RBC folate was 1549 (sd 378) nmol/l and 1275 (95 % CI 1155, 1409) nmol/l in supplement non-users. This is comparable to findings from the Canadian Health Measures Survey (2007–2009) where mean RBC folate (also measured by immunoassay) was 1142 (95 % CI 1153, 1239) nmol/l in women of childbearing age who did not consume a folic acid supplement( 36 ). These findings are reflective of the mandatory folic acid fortification of white wheat flour in Canada. The relationship of obesity with folate status may be more of a concern in countries where fortification is not widespread and supplement use is lower.

The differential association of obesity with serum folate concentration v. RBC folate concentration observed in the present study deserves attention in research and perinatal health practice alike. The identification of subgroups of women who may be susceptible to low folate status or respond differently to folic acid supplementation will ensure that public health interventions can be tailored to meet the needs of the entire population. Obesity is a known risk factor for a number of adverse maternal and infant outcomes including pre-eclampsia( 37 , 38 ), gestational diabetes( 39 , 40 ) and NTD( 41 ). Folic acid deficiency is a known risk factor for NTD( 42 , 43 ) and may be associated with other pregnancy complications such as pre-eclampsia( 44 , 45 ) and other congenital anomalies( 46 , 47 ). As a result, in the study of the association between folate status and adverse maternal and infant outcomes, it is critical to use the appropriate biological specimens for the measurement of folate. Since BMI is positively associated with RBC folate but inversely associated with serum folate, the observed associations between folate status and pregnancy complications may be overestimated if serum folate is used while underestimated if RBC folate is used. Folate status varies substantially during pregnancy( 8 ), which can further complicate the accurate assessment of folate status.

In summary, we confirmed the differential associations of folate with BMI in pregnant women, indicating that the RBC folate cut-off approach for assessing NTD risk may be limited. Because absorption and metabolism of folate are modified by adiposity, RBC folate may not reflect freely available folate at cellular level in pregnant women.

Acknowledgements

Acknowledgements: The authors thank the staff and pregnant women at The Ottawa Hospital and Kingston General Hospital for their support and participation in this study. Financial support: This research was supported in part by the Canadian Institutes for Health Research (CIHR; grant numbers MOP53188, MOP 82802 and MCT-98030). The CIHR had no role in the design, analysis or writing of this article. Conflict of interest: None. Authorship: S.W.W. designed and initiated the study; S.W.W., M.R. and M.C.W. secured funding and resources for the study; M.S. performed statistical analysis of the data and drafted the manuscript; R.R.W. managed the implementation of the study; S.H.C., A.J.M., L.G., G.N.S., R.R.W. and S.W.W. made critical revisions to the manuscript; all authors reviewed and approved the manuscript. Ethics of human subject participation: This study was conducted according to the guidelines laid down in the Declaration of Helsinki and all procedures involving patients were approved by the research ethics boards of The Ottawa Hospital and Kingston General Hospital. Written informed consent was obtained from all patients.

References

  • 1. Kimmons JE, Blanck HM, Tohill BC et al. (2006) Associations between body mass index and the prevalence of low micronutrient levels among US adults. Med Gen Med 8, 59. [PMC free article] [PubMed] [Google Scholar]
  • 2. Bird JK, Ronnenberg AG, Choi SW et al. (2015) Obesity is associated with increased red blood cell folate despite lower dietary intakes and serum concentrations. J Nutr 145, 79–86. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 3. Mojtabai R (2004) Body mass index and serum folate in childbearing age women. Eur J Epidemiol 19, 1029–1036. [DOI] [PubMed] [Google Scholar]
  • 4. Mahabir S, Ettinger S, Johnson L et al. (2008) Measures of adiposity and body fat distribution in relation to serum folate levels in postmenopausal women in a feeding study. Eur J Clin Nutr 62, 644–650. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 5. Tinker SC, Hamner HC, Berry RJ et al. (2012) Does obesity modify the association of supplemental folic acid with folate status among nonpregnant women of childbearing age in the United States? Birth Defects Res Part A Clin Mol Teratol 94, 749–755. [DOI] [PubMed] [Google Scholar]
  • 6. Stern SJ, Matok I, Kapur B et al. (2011) A comparison of folic acid pharmacokinetics in obese and nonobese women of childbearing age. Ther Drug Monit 33, 336–340. [DOI] [PubMed] [Google Scholar]
  • 7. da Silva VR, Hausman DB, Kauwell GP et al. (2013) Obesity affects short-term folate pharmacokinetics in women of childbearing age. Int J Obes (Lond) 37, 1608–1610. [DOI] [PubMed] [Google Scholar]
  • 8. Higgins JR, Quinlivan EP, McPartlin J et al. (2000) The relationship between increased folate catabolism and the increased requirement for folate in pregnancy. BJOG 107, 1149–1154. [DOI] [PubMed] [Google Scholar]
  • 9. Walker MC, Smith GN, Perkins SL et al. (1999) Changes in homocysteine levels during normal pregnancy. Am J Obstet Gynecol 180, 660–664. [DOI] [PubMed] [Google Scholar]
  • 10. Açkurt F, Wetherilt H, Löker M et al. (1995) Biochemical assessment of nutritional status in pre- and post-natal Turkish women and outcome of pregnancy. Eur J Clin Nutr 49, 613–622. [PubMed] [Google Scholar]
  • 11. Walker MC, Finkelstein SA, Rennicks White R et al. (2011) The Ottawa and Kingston (OaK) Birth Cohort: development and achievements. J Obstet Gynaecol Can 33, 1124–1133. [DOI] [PubMed] [Google Scholar]
  • 12. Di Cristofaro J, Silvy M, Chiaroni J et al. (2010) Single PCR multiplex SNaPshot reaction for detection of eleven blood group nucleotide polymorphisms: optimization, validation, and one year of routine clinical use. J Mol Diagn 12, 453–460. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 13. Ferraro ZM, Barrowman N, Prud’homme D et al. (2012) Excessive gestational weight gain predicts large for gestational age neonates independent of maternal body mass index. J Matern Fetal Neonatal Med 25, 538–542. [DOI] [PubMed] [Google Scholar]
  • 14. Kim H, Hwang JY, Kim KN et al. (2012) Relationship between body-mass index and serum folate concentrations in pregnant women. Eur J Clin Nutr 66, 136–138. [DOI] [PubMed] [Google Scholar]
  • 15. Tsang BL, Devine OJ, Cordero AM et al. (2015) Assessing the association between the methylenetetrahydrofolate reductase (MTHFR) 677C→T polymorphism and blood folate concentrations: a systematic review and meta-analysis of trials and observational studies. Am J Clin Nutr 101, 1286–1294. [DOI] [PubMed] [Google Scholar]
  • 16. Bagley PJ & Selhub J (1998) A common mutation in the methylenetetrahydrofolate reductase gene is associated with an accumulation of formylated tetrahydrofolates in red blood cells. Proc Natl Acad Sci U S A 95, 13217–13220. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 17. Scagliusi FB, Polacow VO, Artioli GG et al. (2003) Selective underreporting of energy intake in women: magnitude, determinants, and effect of training. J Am Diet Assoc 103, 1306–1313. [DOI] [PubMed] [Google Scholar]
  • 18. Scagliusi FB, Ferriolli E, Pfrimer K et al. (2009) Characteristics of women who frequently under report their energy intake: a doubly labelled water study. Eur J Clin Nutr 63, 1192–1199. [DOI] [PubMed] [Google Scholar]
  • 19. Prinz-Langenohl R, Brönstrup A, Thorand B et al. (1999) Availability of food folate in humans. J Nutr 129, 913–916. [DOI] [PubMed] [Google Scholar]
  • 20. Babu S & Srikantia SG (1976) Availability of folates from some foods. Am J Clin Nutr 29, 376–379. [DOI] [PubMed] [Google Scholar]
  • 21. Obeid R, Koletzko B & Pietrzik K (2014) Critical evaluation of lowering the recommended dietary intake of folate. Clin Nutr 33, 252–259. [DOI] [PubMed] [Google Scholar]
  • 22. Institute of Medicine (2009) Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: National Academies Press, National Academy of Sciences. [PubMed] [Google Scholar]
  • 23. Bailey LB (2009) Folate in Health and Disease, 2nd ed. Boca Raton, FL: CRC Press. [Google Scholar]
  • 24. Said HM, Chatterjee N, Haq RU et al. (2000) Adaptive regulation of intestinal folate uptake: effect of dietary folate deficiency. Am J Physiol Cell Physiol 279, C1889–C1895. [DOI] [PubMed] [Google Scholar]
  • 25. Subramanian VS, Chatterjee N & Said HM (2003) Folate uptake in the human intestine: promoter activity and effect of folate deficiency. J Cell Physiol 196, 403–408. [DOI] [PubMed] [Google Scholar]
  • 26. Ashokkumar B, Mohammed ZM, Vaziri ND et al. (2007) Effect of folate oversupplementation on folate uptake by human intestinal and renal epithelial cells. Am J Clin Nutr 86, 159–166. [DOI] [PubMed] [Google Scholar]
  • 27. Yasuda S, Hasui S, Yamamoto C et al. (2008) Placental folate transport during pregnancy. Biosci Biotechnol Biochem 72, 2277–2284. [DOI] [PubMed] [Google Scholar]
  • 28. Solanky N, Requena Jimenez A, D’Souza SW et al. (2010) Expression of folate transporters in human placenta and implications for homocysteine metabolism. Placenta 31, 134–143. [DOI] [PubMed] [Google Scholar]
  • 29. McMahon DM, Liu J, Zhang H et al. (2013) Maternal obesity, folate intake, and neural tube defects in offspring. Birth Defects Res Part A Clin Mol Teratol 97, 115–122. [DOI] [PubMed] [Google Scholar]
  • 30. Gao LJ, Wang ZP, Lu QB et al. (2013) Maternal overweight and obesity and the risk of neural tube defects: a case–control study in China. Birth Defects Res Part A Clin Mol Teratol 97, 161–165. [DOI] [PubMed] [Google Scholar]
  • 31. Shaw GM, Velie EM & Schaffer D (1996) Risk of neural tube defect-affected pregnancies among obese women. JAMA 275, 1093–1096. [DOI] [PubMed] [Google Scholar]
  • 32. Waller DK, Shaw GM, Rasmussen SA et al. (2007) Prepregnancy obesity as a risk factor for structural birth defects. Arch Pediatr Adolesc Med 161, 745–750. [DOI] [PubMed] [Google Scholar]
  • 33. Parker SE, Yazdy MM, Tinker SC et al. (2013) The impact of folic acid intake on the association among diabetes mellitus, obesity, and spina bifida. Am J Obstet Gynecol 209, 239.e1–e8. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 34. World Health Organization (2015) Optimal Serum and Red Blood Cell Folate Concentrations in Women of Reproductive Age for Prevention of Neural Tube Defects. Geneva: WHO. [PubMed] [Google Scholar]
  • 35. Daly LE, Kirke PN, Molloy A et al. (1995) Folate levels and neural tube defects. Implications for prevention. JAMA 274, 1698–1702. [DOI] [PubMed] [Google Scholar]
  • 36. Shi Y, De Groh M & MacFarlane AJ (2014) Socio-demographic and lifestyle factors associated with folate status among non-supplement-consuming Canadian women of childbearing age. Can J Public Health 105, e166–e171. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 37. Lisonkova S & Joseph KS (2013) Incidence of preeclampsia: risk factors and outcomes associated with early- versus late-onset disease. Am J Obstet Gynecol 209, 544.e1–544.e12. [DOI] [PubMed] [Google Scholar]
  • 38. Roberts JM, Bodnar LM, Patrick TE et al. (2011) The role of obesity in preeclampsia. Pregnancy Hypertens 1, 6–16. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 39. Baci Y, Üstüner I, Keskin HL et al. (2013) Effect of maternal obesity and weight gain on gestational diabetes mellitus. Gynecol Endocrinol 29, 133–136. [DOI] [PubMed] [Google Scholar]
  • 40. Chu SY, Callaghan WM, Kim SY et al. (2007) Maternal obesity and risk of gestational diabetes mellitus. Diabetes Care 30, 2070–2076. [DOI] [PubMed] [Google Scholar]
  • 41. Rasmussen SA, Chu SY, Kim SY et al. (2008) Maternal obesity and risk of neural tube defects: a metaanalysis. Am J Obstet Gynecol 198, 611–619. [DOI] [PubMed] [Google Scholar]
  • 42. Czeizel A & Dudas I (1992) Prevention of the first occurrence of neural-tube defects by periconceptional vitamin supplementation. N Engl J Med 327, 1832–1835. [DOI] [PubMed] [Google Scholar]
  • 43. MRC Vitamin Study Research Group (1991) Prevention of neural tube defects: results of the Medical Research Council Vitamin Study. Lancet 338, 132–137. [PubMed] [Google Scholar]
  • 44. Wen SW, Champagne J, Rennicks White R et al. (2013) Effect of folic acid supplementation in pregnancy on preeclampsia: the folic acid clinical trial study. J Pregnancy 2013, 294312. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 45. Wen SW, Chen XK, Rodger M et al. (2008) Folic acid supplementation in early second trimester and the risk of preeclampsia. Am J Obstet Gynecol 198, 45.e1–e7. [DOI] [PubMed] [Google Scholar]
  • 46. Pei L, Zhu H, Zhu J et al. (2006) Genetic variation of infant reduced folate carrier (A80G) and risk of orofacial defects and congenital heart defects in China. Ann Epidemiol 16, 352–356. [DOI] [PubMed] [Google Scholar]
  • 47. Feng Y, Wang S, Chen R et al. (2015) Maternal folic acid supplementation and the risk of congenital heart defects in offspring: a meta-analysis of epidemiological observational studies. Sci Rep 5, 8506. [DOI] [PMC free article] [PubMed] [Google Scholar]

Articles from Public Health Nutrition are provided here courtesy of Cambridge University Press

RESOURCES