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Background: Neural tube defects (NTDs) and Down syndrome (DS) are two of the commonest birth defects prevalent in India. Though the etiologies of these defects are multifactorial, it has long been speculated that maternal nutrition is a contributing risk factor.
Objective: To draw an understanding between the association of birth defects and sufficiency and quality of maternal nutritional intake in an Indian cohort.
Design: Analysis of a 24 hour dietary recall and food frequency questionnaire was used to quantify individual food consumption in terms of total calories, carbohydrates, proteins, fats and vitamins in a study group comprising of 75 NTD mothers, 102 DS mothers and 104 matched controls. Dietary data was compared to ICMR and USDA nutritional guidelines for women.
Results: 25 - 100% women were found to be consuming lower than recommended measures of different food groups with respect to the ICMR guidelines and 5 - 99% women were defaulters as per the USDA guidelines. Only vitamin B12 intake was significantly low in DS mothers compared to control-mothers (0.46±0.04 µg / day and 1.3±0.14 µg / day respectively, p = 0.023).
Conclusions: There was an overall deficiency given the up to 2000 Calories limit for sedentary women. Folic acid and vitamin B12 estimates were low compared to the more recent USDA guidelines. Neither folic acid nor vitamin B6 was found to be significantly associated with the risk of NTD or DS, low vitamin B12 may be a risk factor for DS.
Keywords: Maternal nutrition, dietary assessment, neural tube defects, Down syndrome
The maternal diet and wellness, both before the onset and during pregnancy are crucial to the prospects of the offspring's. Every expectant woman needs a good mixed diet that provides both adequate calories and nutrition since the growth of the developing fetus is almost entirely dependant on the provision of nutrition via maternal blood supply. Fetal development involves continuous cell proliferation, differentiation and the formation of tissues and organs. All manner of cellular activities proceed via extensive replication of DNA alongside dynamic changes in patterns of expression of a large number of developmentally regulated genes. The precise regulation of gene expression, the surrounding placental environment; including the maternal nutrition state are important contributors to the completion of normal morphogenesis. When any of these processes goes awry - because of disease or interference in normal progression of development - the consequences can be disastrous.
Abundant experimental and epidemiological data under the aegis of nutritional genomics attempts to demonstrate how nutrition influences homeostasis and the influence of dietary nutrients on the genome; such as the association of congenital anomalies with maternal nutrition and genetic factors. Vitamins and micronutrients are now well acknowledged as crucial cofactors in metabolic pathways that regulate nucleic acids synthesis and / or repair systems as well as the expression of genes3. Folic acid, vitamin B6 and B12 are three such vital micronutrients; deficiencies of which have been speculated to result in abnormal embryogenesis primarily via disruption of genomic integrity and affecting gene expression through alteration in DNA methylation: a major epigenetic feature of DNA that regulates gene transcription4. Folic acid is an important precursor of the one - carbon metabolism or the homocysteine remethylation pathway. Vitamin B6 is a cofactor of cystathionine ß synthase (EC...) and vitamin B12 is a cofactor of methionine synthase (EC...) in the same pathway. The ability of these micronutrients along with adequate quality nutrition to modulate the risk of birth defects is currently subject of much research globally. On similar lines we examined the association of maternal nutrition with two unrelated congenital birth defects, namely, NTDs and DS in the Indian population.
NTDs are actually a range of congenital malformations associated with the failure of the neural tube to close properly during early embryonic development that can lead to severe disability or even death. NTDs are physiological abnormalities with no single or attributable underlying genetic origin. The defect actually occurs at about the end of the first month after conception, at a time when most women do not even realize they are pregnant! It is hypothesized that the effect of restrictive stresses can be more profound during early pregnancy and the development of the baby's brain and neurological system is at risk during the vulnerable period76. The etiology of NTDs is multifactorial and the exact mechanisms of their occurrence are not known. Even as embryologists and geneticists try to elucidate the basis of neurulation, most of our understanding of NTDs comes from studies in mouse and amphibian models, for obvious reasons! [Frequency]
DS is another congenital disorder; a chromosomal abnormality characterized with presence of a third copy of chromosome 21 seen in the affected individual. DS is the most common cause of mental retardation [Sheth, 2003]. The chromosomal abnormality is often associated with varying types and degrees of physiological complications whose cumulative understanding is far from complete. However, abnormal chromosomal segregation during meiosis at oocyte maturation upon the initiation of ovulation in the sexually mature female leading to disomic maternal gametes has been proposed to be the primary cause of Down syndrome in more than 90% of the cases [ref]. [Frequency]
NTD and DS in the same family...
With the view of promoting good health in the general population usually with special emphasis on women of child - bearing age, government agencies issue directives or guidelines targeted to guiding both medical practitioners and the public alike. The essence of these guidelines is to bestow the ability of maintaining good nutrition coupled to healthy lifestyles alongside reducing the burden of disease. With women these guidelines aim at the optimization of maternal health reducing the risk and incidence of birth defects and the occurrence of chronic ailments by achieving optimal foetal growth and development. The Recommendations of the Indian Council of Medical Research (ICMR) Nutrition Expert Group (1968) and the United States Department of Agriculture's (USDA) Dietary Guidelines for Americans (2005) are two such guidelines that we have referred to in the current study.
Materials and Methods
The study group comprised of Indian women having a history of progeny with NTD or DS (case group), and age - and geographical origin - matched women with healthy offspring (control group). History of / or concomitant major illness namely cancer, renal or liver disease, or participation in another clinical trial within a month of enrolment in the present study, or refusal to give written informed consent for participation in the study comprised the exclusion criteria.
Seventy five women who gave birth to children with NTDs (74 mothers having children with NTDs, and 1 mother having a child with both a NTD and DS) and 102 women who gave birth to children with DS were enrolled along with 104 control mothers. Enrollment of women in the study involved the completion of an exhaustive CRF containing enrollment information, demographic data, medical and obstetric history, and diet assessments.
A single 24 hour dietary recall coupled to a food frequency questionnaire formed the basis of dietary assessment. The prime objective of the dietary recall interviews was to estimate total intake of food energy (calories), nutrients and micronutrients from foods and beverages that were consumed during the 24 hour period prior to the interview. Diet preference (vegetarian / mixed diet) was documented. During the dietary recall, participants reported details of the previous day's meal from early morning until bedtime along with vitamin supplementation. Standard measuring cups were used to aid participants in the dietary recall. The food frequency questionnaire examined information pertaining to the number of times food items such as fruits, salads, green leafy vegetables, dark vegetables, meat, fried foods, snacks, pizzas, burgers and aerated drinks etc. were consumed. Information regarding the amount of edible oils (and type), ghee, butter, hydrogenated fats and cheese consumed was used to calculate the average per capita consumption.
The study was approved by Institutional Ethics Committee. Enrolment of women in the study was subject to their providing written informed consent after being explained about the project. For the ease of participants the Informed Consent Form were prepared in English, Hindi and Marathi. If the participant was illiterate, consent was obtained by taking a thumb impression on the ICF after duly explaining the project in the presence of a family member and a doctor or a paramedic.
All data obtained from the CRFs was entered into computer databases which were used for selective retrieval to facilitate statistical analysis. Microsoft Excel 2007 (Microsoft, WA, USA) and SPSS v15 (Chicago, IL, USA) were used for statistical analyses of data.
The dietary recall data was analyzed for carbohydrate, protein, fats, vitamins B6 and B12, folic acid and total calories consumed using published exchange values. Micronutrient intake of case - and control - mothers was analyzed by t - test.
Dietary data was carefully divided into seven groups, namely: fruits, vegetables, grains, meat (and beans), milk, oils (and fats) and discretionary calorie allowances as per the USDA and ICMR Food Guides for sedentary adult women detailed in Table 1.
Mothers in the cases and control groups were matched for region of origin and consisted of Maharashtrians, Gujaratis, North Indians, and South Indians.
The mean maternal age (± standard deviation) of control mothers was 38 ± 8 years (n = 104) that of NTD mothers was 34 ± 8 years (n = 72) and of DS mothers was 38 ± 9 years (n=102).
More numbers of control mothers were graduates and post - graduates compared to the case mothers who were mostly school dropouts and matriculate. Annual income of control mothers was higher than that of case mothers. Most case mothers belonged to the poorer strata, or were from the lower middle class whereas most control mothers were from the upper middle class. More numbers of the control mothers were employed while more case mothers were housewives.
46% of control mothers, 27% of NTD mothers and 40% of DS mothers were vegetarians while the rest preferred a mixed diet. The BMIs were comparable across groups (25 ± 4 kg / m2, 25 ± 5 kg / m2 and 24 ± 5 kg / m2 for control, NTD and DS mothers respectively). Diabetes and Hypertension were fairly uncommon and most of those affected took prescribed medication, this along with consumption of different types of supplements has been summarized in Table 4.
When dietary data of the study mothers was compared to those given in the dietary guidelines, 25 - 100% women were found to be consuming lower than recommended measures of different food groups with respect to the ICMR guidelines and 5 - 99% women were defaulters as per the USDA guidelines, the details of which are reflected in Graphs 1 and 2.
The mean maternal ages across groups were comparable. It was observed that control mothers were more educated compared to case mothers.
Although dietary assessments of mothers were made at the time of enrolment which in most cases was after a substantial period since child birth, this may nevertheless reflect the mother's diet around child birth particularly in terms of diet preference and method of food preparation that do not change drastically over time.
Means of BMI were comparable between both study groups. Calorific intake throughout the cohort was lower than the 2000 calories / day recommendation of both the ICMR and USDA.
From the dietary intake calculations, it was found that the intake of folic acid in the cohort was sufficient as per ICMR guidelines (100 µg / day) although low as compared with the US Recommended Daily Allowance (RDA) of 400 µg / day according to Institute of Medicine (IOM) of the United States National Academy of Science. This could be attributed to the insufficient consumption of vegetables and meat across groups further complexed by population diversity and the prevalence of rigid socio - economic systems. There is also the wide prevalence of regional cuisines, the tradition of milling grains at small local mills sans fortification, high temperature cooking and the practice of largely consuming home cooked meals that affect the sufficiency and bioavailability of folates from food.
Vitamin B12 intake of control and NTD mothers was adequate according to Indian RDA of 1 µg / day, though it was significantly low in DS mothers. However vitamin B12 intake was lower throughout the cohort compared to the US DRI of 2.4 µg / day. Other studies have also reported such rampant deficiency in the Indian population [ref paper2.docx pg 12 and Yajnik et al., 2005]. Given that all requirement of vitamin B12 comes from food of animal origin, the sole factor that could be attributed to this endemic is the archaic vegetarianism of the major chunk of the population due to religion primarily and socio - economic reasons to a smaller extent. Growth retardation, delayed psychomotor development and sometimes permanent effects on the child's developing brain have been linked with even a mild maternal vitamin B12 deficiency [Schneede et al., 1994]. Also, low dietary intake of vitamin B12 or mal-absorption has been implicated as high risk factor for NTDs [Allen et al., 1995; Botto et al., 1999]. Low vitamin B12 status has also been associated with high plasma total homocysteine concentrations in Indians [Refsum et al., 2001]. Methionine synthase (MTR) remethylates homocysteine to methionine using vitamin B12 as cofactor. Reduced homocysteine remethylation and consequently less SAM generation due to reduced MTR activity because of inadequate vitamin B12 could be the cause of the reported high homocysteine. Lower SAM generation is then likely to result in DNA hypo-methylation. DNA hypo-methylation has been linked to abnormal chromosomal segregation [Rosenblatt, 1999], and thereby; the increased likelihood of DS in the baby.
Vitamin B6 intake was adequate according to both the Indian RDA (2 mg / day) and US RDA (1.3 mg / day) [ref].
More number of control mothers consumed supplements (Iron, Calcium and multi- vitamin) compared to case groups. There is some evidence of socio-economic status and education having an impact on the awareness in women on the consumption of supplements.
A 24 hour dietary recall coupled to food frequency questionnaire serves as a reasonable measure of estimating an individual's nutrient intake; however these are not free of limitations that might occur due to the retrospective nature of the study and errors due to recall bias.
Low vitamin B12 may be a contributing factor to the aetiology of DS, underpinning its crucial role in cellular development. Neither folic acid nor vitamin B6 was found to be significantly associated with the risk of NTD or DS. Efforts to increase awareness in women of child bearing age, about usage of micronutrient and the inability of strict vegetarian diets in providing these should nevertheless be intensified. Given the trend of poor consumption of supplements and their low palatability in apparently healthy women, the main focus of such awareness programmes should be the promotion of achieving ideal nutrition via diet with reducing dependency on supplements.