Introduction

Deficiencies of folate and vitamin B₁₂, both prenatal and early childhood, are associated respectively with slower child neurodevelopment. Brain development begins in the prenatal period and continues through puberty with rapid growth in the first two years of life.^1,2

Folate is involved in DNA synthesis, proliferation, differentiation and apoptosis of neural stem cells.³ Vitamin B₁₂ plays an important role in the conversion of phosphatidylethanolamine to phosphatidylcholine, which comprise 14 and 11% of the myelin from the central neural system, respectively.⁴

There is consistent evidence showing a positive association of dietary intake and/or plasma concentration of folate and vitamin B₁₂ from the mother during pregnancy with the mental development of children.¹ However, information about plasma concentrations and/or dietary intake of folate and vitamin B₁₂ from the child in relation to their neurodevelopment is scarce. At 18 months of age, plasma concentrations of folate and vitamin B₁₂ are positively associated with mental development.⁵ Also, in a study with adolescents a lower cognitive function was detected among those who consumed a macrobiotic diet (cereals, pulses, and vegetables, with small additions of seaweed, fermented foods, nuts, seeds, and seasonal fruit; fish occasionally; meat and dairy products avoided) until six years of age, compared to those who consumed an omnivorous diet.⁶ Additionally, in a randomized clinical trial, children from 6 to 30 months of age were supplemented for six months with folic acid (150 µg) and vitamin B₁₂ (1.8 µg); an increase was observed in the gross motor development as well as in problems solution.⁷

The aim of this study was to evaluate the association of dietary intake of folate and vitamin B₁₂ with mental and psychomotor development, at 24 and 30 months of age, in a cohort of Mexican children.

Materials and methods

This study is derived from a perinatal prospective cohort which was conducted in four municipalities in the state of Morelos, Mexico between 2001 and 2009. The detailed methodology has been previously described.^8,9 From a total of 442 births that occurred in that period, 229 children had information about: dietary intake and neurodevelopment assessment at 24 and/or 30 months of age, and were included in this report; 41 children were considered ineligible for presenting cerebral atrophy, prematurity (<37 weeks), neonatal death, congenital hypothyroidism, cleft lip/palate, perinatal asphyxia, birth weight <2 kg, coming from a twin birth and/or mother had ≤15 years of age; 102 were lost to follow-up; 69 were excluded for not having information of interest and one had a total energy intake ~4000 Kcal which was considered implausible. Maternal information about socio-demographic characteristics, dietary habits, gynecological and obstetric history, tobacco and alcohol consumption, breastfeeding, among others was also available.

This study was approved by the Ethics Committee of the National Public Health Institute of Mexico. Informed consents were obtained from study participants at the baseline and an informed re-consent letter was obtained for the evaluation of children.

Results

The mothers of the children in the study were young (22 years old), mostly primiparous (81.2%), with an average schooling of almost 11 years, an IQ of 88.6 ± 12.7 and a normal BMI at first trimester (23.5 ± 3.9 kg/m²). Only 7.5% reported having smoked and 24.2% were exposed to secondhand smoke during pregnancy. Most mothers (~85%) had a poor dietary intake of iron during the first and third trimester of pregnancy. Approximately 59% of children were born by cesarean section, 8.3% did not receive breastfeeding and had on average 30.8 ± 4.7 points in HOME scale (table I).

Table I. Parental, child and family selected characteristics among included, excluded and lost children in the study. Morelos, Mexico 2001-2009 

^* At 1st trimester of pregnancy

^‡ P<0.05

Compared with children who were excluded or lost in the postnatal follow-up (n =172), a higher percentage (69.4%) of children included in this study it received more than 12 weeks of breastfeeding and had parents with less schooling (table I).

On average, girls had higher MDI at both ages, however this difference was not statistically significant. In contrast, the PDI was significantly higher in boys than in girls, although only at 24 months old. No significant differences were observed in dietary variables under study according to gender or age at evaluation (table II). Low dietary intake of folate and vitamin B₁₂ was observed in a very small percentage of boys (from 0.79 to 3.97%) and girls (from 0.97 to 1.94%) at both 24 and 30 months of age (data not included). An increase in MDI with increased dietary folate was observed at 30 months of age (p=0.06) (table III).

Table II Child neurodevelopment and dietetic folate, vitamin B₁₂ and total energy according to age at evaluation. Morelos, Mexico 2001-2009 

^* At 24 months boys vs. girls (p<0.001)

^‡ As dietary folate equivalents

Table III Mixed models coefficients of dietary folate^* or vitamin B₁₂^* with neurodevelopment according to age at evaluation. Morelos, Mexico 2001-2009 

^* Energy-adjusted

^‡ As dietary folate equivalents

^§ Adjusted by maternal schooling, HOME, parity, child birthweight and z score of child BMI

^# Adjusted by maternal schooling, IQ, HOME, paternal schooling and child birthweight

^& Adjusted by maternal schooling, HOME, parity, BMI at 1^st trimester of pregnancy, paternal schooling, child sex, birthweight, and z score of child BMI

^≠ Adjusted by maternal schooling, maternal IQ, HOME, dietary iron intake at 3^rd trimester and BMI at 1st trimester, paternal schooling, child sex, birthweight and z score of child BMI

∞ p value=0.06

Sample sizes are different due to missing values in one or more covariables

Discussion

The results of this study may indicate increased child neurodevelopment associated with dietary folate intake. Also, they weakly suggest that dietary vitamin B₁₂ intake may have a positive association with child neurodevelopment.

Although we do not identify previous studies that would have evaluated the association between dietary folate and vitamin B₁₂ intake with child neurodevelopment, our results are similar to those reported in a study of about 500 children in northern India, where plasma concentrations of folate and vitamin B₁₂ were significantly associated with mental development at 18 months of age. Also the increment in mental development associated with folate was not observed in children with low plasma vitamin B₁₂ concentrations (<25th percentile). In our study it was not possible to evaluate the association of folate through defined strata of dietary intake of vitamin B₁₂ by a reduced sample size. In addition, our results show no association between child dietary intake of folate and vitamin B₁₂ with psychomotor development, which also was observed in the study described previously.⁵ It is possible that the lack of significance in the results of our study is explained not only by the small sample size but also by the use of the food frequency questionnaire that may have low sensitivity and specificity,¹⁷ and it has also been observed elsewhere.¹⁸ We are aware that a limitation of this study is that due to the small sample size, other nutrients related with child neurodevelopment such as iron, zinc and ω-3 PUFAs could not be analyzed.

Not only is postnatal child dietary intake of folate and vitamin B₁₂ is associated with their mental development, but so is the maternal intake of these nutrients during pregnancy.³ Previously, in mothers of children under study it was found that vitamin B₁₂ deficiency significantly reduced mental development during the first year of life (β=-1.6; 95%CI=-2.8 to -0.3). Also, dietary folate was negatively associated with mental development among offspring whose mothers were genetically susceptible (carriers of MTHFR 677TT genotype) with a dietary folate intake <400 mg/day (β=-1.8; 95%CI=-3.6 to -0.04).¹⁹

Experiments have shown that folate has specific effects on the central nervous system from the embryonic period to adulthood; it is involved in neurogenesis, proliferation, migration, neuronal differentiation and synaptic plasticity.²⁰ Its deficiency in breast feeding alters behavior and learning ability²¹ and in adulthood promotes sensory axonal regeneration.²² Folate stimulates the Notch signaling pathway and Erk 1/2 phosphorylation, participates in the biosynthesis of neurotransmitters and epigenetic mechanisms that partially explain the above effects.^20,21,23 With folate, vitamin B₁₂ is involved in the cycle of one carbon that is essential for the synthesis and integrity of the genome,²³ it contributes to the formation of myelin and the functioning of the central nervous system.²⁴

It is important to note some methodological considerations for interpreting our results. Initially, it was found that participating children received breastfeeding longer and their parents had less schooling than those who were lost or excluded from the study. This reduces the generalizability of our results. It is possible that the reported associations in this study are a conservative estimate due to random measurement error inherent to the food frequency questionnaire used to estimate dietary folate and vitamin B₁₂. However, in this respect, it was found that the total daily energy intake by the study children was similar not only to that reported in children from one to four years in the National Health and Nutrition Survey of Mexico,²⁵ but also to the recommendations of the IOM of the United States for children from one to three years.²⁶ Additionally, provisions were taken to reduce the possibility of a differential error, which included blinding of the child dietary intake to the psychologists who applied the BSID-II test as well as blinding of the child neurodevelopment status to the interviewers who collect information about child dietary intake. Moreover, it is unlikely our results are explained by confounders (i.e., home environment, breastfeeding, and maternal IQ) that were taken into account in the multivariate models. Also, in a subsample of the study population, adjustment by hemoglobin at 24 months of age (n=90), because anemia in preschoolers is highly prevalent (20.4% in 2012),²⁷ or maternal plasma folate and/or vitamin B₁₂ at first trimester of pregnancy, did not change the results (n=133) (data not shown).

In conclusion, our results suggest that dietary folate intake in early childhood may benefit the mental development of children.