Maternal dietary fibre intake during pregnancy and behavioural problems in 5-year-old children: the Kyushu Okinawa Maternal and Child Health Study

Abstract

Objective

Consumption of dietary fibre has various beneficial effects on human health. In this prebirth cohort study, we examined the association between maternal dietary fibre intake during pregnancy and the risk of childhood behavioural problems in 5-year-old Japanese children.

Method

Participants were 1199 mother–child pairs. Maternal dietary intake was assessed using a diet history questionnaire. Emotional problems, conduct problems, hyperactivity problems, peer problems and low prosocial behaviour in children were assessed using the parent-reported version of the Strengths and Difficulties Questionnaire.

Results

Significant inverse exposure–response associations were observed between maternal total dietary fibre consumption during pregnancy and the risk of childhood hyperactivity problems and low prosocial behaviour: the adjusted ORs (95% CIs, P for trend) between extreme quartiles were 0.55 (0.33 to 0.90, 0.02) and 0.64 (0.44 to 0.93, 0.004), respectively. Maternal consumption of soluble dietary fibre during pregnancy was independently inversely associated with childhood hyperactivity problems: the adjusted OR (95% CI, P for trend) between extreme quartiles was 0.57 (0.34 to 0.94, 0.03). Maternal consumption of insoluble dietary fibre during pregnancy was independently inversely associated with both hyperactivity problems and low prosocial behaviour in children: the adjusted ORs (95% CIs, P for trend) between extreme quartiles were 0.48 (0.29 to 0.80, 0.009) and 0.63 (0.43 to 0.91, 0.008), respectively. There were no associations between maternal consumption of total, soluble or insoluble dietary fibre during pregnancy and childhood emotional, conduct or peer problems.

Conclusions

Higher maternal intake levels of total dietary fibre and insoluble dietary fibre during pregnancy may be associated with a decreased risk of hyperactivity problems and a decreased risk of low prosocial behaviour in 5-year-old children. Maternal soluble dietary fibre during pregnancy may be inversely associated with childhood hyperactivity problems.

WHAT IS ALREADY KNOWN ON THIS TOPIC.

WHAT THIS STUDY ADDS

• Maternal intake levels of total dietary fibre and insoluble dietary fibre during pregnancy were inversely associated with the risk of hyperactivity problems and low prosocial behaviour in 5-year-old children. Maternal soluble dietary fibre during pregnancy was inversely associated with childhood hyperactivity problems.

HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY

• We recognise the need for additional epidemiological studies and research investigating the mechanisms that underlie these observed inverse associations.

Introduction

The definition of dietary fibre that is largely adopted with minor modifications in most countries states: ‘Dietary fibre means carbohydrate (CHO) polymers with 10 or more monomeric units, which are not hydrolyzed by the endogenous enzymes in the small intestine of humans and belong to the following categories: edible CHO polymers naturally occurring in the food as consumed; CHO polymers obtained from food raw material by physical, enzymatic or chemical means; synthetic CHO polymers’.¹ Dietary fibre is classified into soluble and insoluble fibre depending on their water solubility.¹ The main food sources of dietary fibre include whole grains, fruits and berries, vegetables, nuts and seeds and legumes.¹ Adequate consumption of dietary fibre is recognised as important for human health, with higher intakes of dietary fibre reducing the risk of several chronic diseases such as cardiovascular disease, type 2 diabetes and some cancers.²

Recent reports have investigated the relationship between maternal intake of dietary fibre during pregnancy and child behavioural development. One study based on 21 852 Norwegian mother–father–child trios showed an association between higher maternal intake of fibre during pregnancy and lower offspring attention-deficit/hyperactivity disorder (ADHD) symptom scores in early childhood (up to 8 years of age).³ Dietary fibre is known to exert neuroprotective effects via the microbiota–gut–brain axis.⁴ Recent animal models demonstrate that maternal high-fibre intake improves social deficits and brain development in offspring by restructuring the maternal gut microbiota and increasing short-chain fatty acid (SCFA) levels.⁵

To provide further evidence for the importance of maternal dietary fibre consumption on child behavioural problems, this study investigates the association between maternal intake of dietary fibre during pregnancy and the risk of behavioural problems in 5-year-old children using data from the Kyushu Okinawa Maternal and Child Health Study (KOMCHS).

Methods

Study population

The KOMCHS is a prospective prebirth cohort study designed to identify risk and preventive factors for maternal and child health issues, such as allergies, developmental disorders and depressive symptoms. Details of the baseline KOMCHS survey have been previously described.⁶ In the baseline survey, eligible participants were women who were pregnant between April 2007 and March 2008, residing in one of the seven prefectures on Kyushu Island, southern Japan (total population approximately 13.26 million), or in Okinawa Prefecture (population nearly 1.37 million). We asked 423 obstetric hospitals in these eight prefectures to distribute information leaflets explaining the KOMCHS, along with an application form to participate and a self-addressed stamped return envelope, to as many pregnant women as possible. Pregnant women who intended to participate mailed the application form to the data management centre. Using the contact information provided, research technicians gave each pregnant woman a detailed explanation of the KOMCHS by telephone and sent a self-administered questionnaire after obtaining verbal consent.

Ultimately, 1757 pregnant women between 5 and 39 weeks of gestation provided written informed consent to participate in the KOMCHS and answered a self-administered questionnaire in the baseline survey. Among these women, 1590, 1527, 1430, 1362, 1305, 1264 and 1201 mother–child pairs participated in the second (postdelivery), third (approximately 4 months post partum), fourth (approximately 12 months post partum), fifth (approximately 24 months post partum), sixth (approximately 36 months post partum), seventh (approximately 48 months post partum) and eighth (approximately 60 months post partum) surveys, respectively. A complete case analysis was performed; two of the 1201 mother–child pairs were excluded due to missing household income data. With no other missing values for exposures, outcomes, or covariates, the final analytic sample consisted of 1199 pairs (figure 1).

Figure 1. Flow chart of the study population.

Measurements

For each survey, study participants completed self-administered questionnaires and mailed them to the data management centre. Research technicians then addressed missing data or clarified illogical data through telephone interviews. The first part of the baseline questionnaire collected information on maternal age, gestation, region of residence, number of children, maternal and paternal educational levels, household income, and depressive symptoms. Depressive symptoms were assessed using the Japanese version of the Centre for Epidemiologic Studies Depression Scale (CES-D).^{7 8} The total CES-D score ranged from 0 to 60, with depressive symptoms defined as a CES-D score ≥16.

The second part of the baseline questionnaire was a semi-quantitative, comprehensive Diet History Questionnaire (DHQ) to assess dietary habits over the preceding month.9,15 Pregnant women were asked to report their average consumption frequency of eight categories of foods and beverages, ranging from ‘never’ to ‘≥2 times/day’ for foods and from ‘<1 time/week’ to ‘≥6 times/day’ for beverages, and their relative portion size in comparison with a standard portion size according to five categories: ‘50% smaller or less,’ ‘20%–30% smaller,’ ‘the same,’ ‘20%–30% larger’ and ‘50% larger or more’.¹⁵ Estimates of daily food intake (among 150 foods), energy and selected nutrients were calculated using an ad hoc computer algorithm for the DHQ based on the Standard Tables of Food Composition in Japan.¹⁶ Energy-adjusted intake, calculated using the residual method, was used for the analyses.¹⁷

The second survey questionnaire gathered data regarding the infant’s sex, birth weight, date of birth and maternal smoking status during pregnancy. Information on household smoking and breastfeeding duration was collected from the questionnaire until the fourth survey. In the eighth survey, children’s behavioural problems were assessed using a Japanese parent-reported version of the Strengths and Difficulties Questionnaire (SDQ), designed to assess the behaviour and emotions of children aged 3 to 16 years.¹⁸ The SDQ consists of five scales: emotional problems, conduct problems, hyperactivity problems, peer problems and prosocial behaviour. Each scale includes five items, resulting in a total of 25 items. Each item was rated on a three-point scale: ‘not true’ (0); ‘somewhat true’ (1); and ‘certainly true’ (2). Positively worded items were reverse-scored. The items on each scale were summed to generate scores ranging from 0 to 10. A high score on the prosocial scale reflects strengths, whereas high scores on the other four scales indicate difficulties. These scale scores were then categorised as normal, borderline or abnormal based on cut-off points previously reported in a sample of Japanese children.¹⁹

Statistical analyses

The five scale scores were dichotomised, comparing children with borderline and abnormal scores to children with normal scores. Emotional problems, conduct problems, hyperactivity problems, peer problems and low prosocial behaviour were defined as present when a child had a borderline or abnormal score in the respective scale (>3, >3, >5, >3 and <6, respectively). Intake of each dietary factor under study was categorised into quartiles based on its distribution among the 1199 mothers. A priori, we selected maternal age, gestation at baseline, region of residence at baseline, number of children at baseline, maternal and paternal education, household income, maternal depressive symptoms during pregnancy, maternal alcohol intake during pregnancy, maternal smoking during pregnancy, child’s birth weight, child’s sex, secondhand smoke exposure at home during the first year of life and breastfeeding duration as potential confounding factors. Maternal age, gestation and birth weight were used as continuous variables. In our previous studies using data from the KOMCHS, maternal intake levels of several specific nutrients and food groups during pregnancy were associated with different domains of childhood behavioural problems.20,29 To avoid overadjustment bias and maintain the interpretability of the results, we did not adjust for all previously reported nutritional factors in the KOMCHS, as many of these variables may be highly intercorrelated.2023,27

Multiple logistic regression analysis was conducted to estimate the adjusted ORs and 95% CIs for each behavioural problem according to the intake quartiles for dietary fibre (total dietary fibre, soluble dietary fibre and insoluble dietary fibre), with the lowest quartile used as the reference. The trend of association was assessed using a logistic regression model assigning consecutive integers (1 to 4) to the intake quartiles for dietary fibre, and two-sided p values <0.05 were considered statistically significant. All computations were performed using the SAS software package V.9.4 (SAS Institute). As this study was characterised as an initial exploratory investigation in this specific population with limited prior data to estimate effect sizes, a formal a priori sample size calculation was not performed. Instead, we included all available participants to maximise statistical power.

Results

Among the 1199 children aged 59 to 71 months, the prevalence values of emotional problems, conduct problems, hyperactivity problems, peer problems and low prosocial behaviour were 12.9%, 19.4%, 13.1%, 8.6% and 29.2%, respectively. The median maternal age and gestation at baseline were 32.0 years (IQR, 29.0–34.0) and 17.0 weeks (IQR, 14.0–21.0), respectively. The median maternal daily consumption of total energy during pregnancy was 7127 kJ (IQR, 6117–8465). The median daily energy-adjusted intake levels of total dietary fibre were 11.8 g (IQR, 10.1–14.4), with soluble dietary fibre at 3.0 g (IQR, 2.5–3.7) and insoluble dietary fibre at 8.4 g (IQR, 7.1–10.1).

Maternal total dietary fibre consumption during pregnancy was inversely associated with maternal depressive symptoms during pregnancy, maternal smoking during pregnancy and smoking in the household during the first year of the child’s life (table 1). Mothers with higher levels of total dietary fibre consumption were more likely to be older, have more years of education, have partners with more years of education, have higher household incomes and to have breastfed their children for 6 months or more.

Table 1. Characteristics of 1199 mother–child pairs, according to quartile (Q) of maternal total dietary fibre intake during pregnancy^*.

		Total (n=1199)†	Total dietary fibre‡
			Q1	Q2	Q3	Q4	P for trend§
Maternal age, years		32.0 (29.0–34.0)	31.0	31.0	32.0	32.0	0.0002
Gestation, weeks		17.0 (14.0–21.0)	17.0	17.0	17.0	17.0	0.56
Region of residence, %	Fukuoka Prefecture	57.8	56.2	56.0	61.7	57.3	0.85
	Other than Fukuoka Prefecture in Kyushu	32.8	32.4	33.0	31.0	34.7
	Okinawa Prefecture	9.4	11.4	11.0	7.3	8.0
Number of living children born to the same mother, %	0	40.4	41.5	45.0	38.3	36.7	0.11
	1	40.0	37.8	38.7	44.0	39.7
	≥2	19.6	20.7	16.3	17.7	23.7
Maternal education, years, %	<13	20.9	26.8	20.7	17.7	18.3	0.006
	13–14	33.3	31.4	35.0	34.7	32.0
	≥15	45.9	41.8	44.3	47.7	49.7
Paternal education, years, %	<13	28.6	33.1	30.0	26.7	24.7	0.008
	13–14	14.4	15.7	14.7	11.7	15.7
	≥15	57.0	51.2	55.3	61.7	59.7
Household income, yen/year, %	<4 000 000	32.2	41.8	31.3	29.3	26.3	0.0003
	4 000 000–5 999 999	37.5	34.8	37.7	33.3	44.0
	≥6 000 000	30.4	23.4	31.0	37.3	29.7
Maternal depressive symptoms during pregnancy, %		18.2	22.4	21.7	14.7	14.0	0.001
Maternal alcohol intake during pregnancy, %		13.2	14.1	14.0	12.7	12.0	0.39
Maternal smoking during pregnancy, %		7.3	12.4	8.0	5.0	3.7	<0.0001
Birth weight, g		3012 (2772–3246)	3026	3020	2999	3015	0.46
Male sex, %		47.4	43.1	45.7	51.3	49.3	0.06
Breastfeeding duration, months, %	<6	10.8	16.4	12.3	7.3	7.3	<0.0001
	≥6	89.2	83.6	87.7	92.7	92.7
Smoking in the household during the first year of life, %		27.4	32.8	29.7	24.7	22.7	0.002

^*Values are medians for continuous variables and percentages of participants for categorical variables.

^†Values are medians (IQRs) for continuous variables and percentages of participants for categorical variables.

^‡The intake range of each quartile was as follows: Q1 (<10.1 g), Q2 (10.1 to <11.8 g), Q3 (11.8 to <14.4 g), Q4 (≥14.4 g).

^§For continuous variables, a linear trend test was used; for categorical variables, a Mantel-Haenszel χ2 test was used.

Compared with maternal consumption of total dietary fibre during pregnancy in the first quartile, consumption in the fourth quartile was independently associated with a reduced risk of hyperactivity problems in children, with a statistically significant inverse linear trend (adjusted OR between extreme quartiles: 0.55, 95% CI 0.33 to 0.90; p for trend=0.02) (table 2). Similarly, compared with maternal consumption of total dietary fibre during pregnancy in the first quartile, consumption in the fourth quartile was independently associated with a reduced risk of low prosocial behaviour in children, with a statistically significant inverse linear trend (adjusted OR between extreme quartiles was 0.64, 95% CI 0.44 to 0.93; p for trend=0.004).

Table 2. ORs and 95% CIs for hyperactivity problems and low prosocial behaviour assessed by the Strengths and Difficulties Questionnaire in 1199 5-year-old children by quartiles of maternal dietary fibre intake during pregnancy.

	Hyperactivity problems		Low prosocial behaviour
Variables*	Risk (%)	Adjusted OR (95% CI)†	Risk (%)	Adjusted OR (95% CI)†
Total dietary fibre
Q1 (8.8)	17.7	1.00	34.5	1.00
Q2 (11.0)	12.7	0.67 (0.42 to 1.07)	32.0	0.89 (0.63 to 1.27)
Q3 (13.1)	12.0	0.64 (0.40 to 1.04)	24.3	0.58 (0.40 to 0.85)
Q4 (16.2)	10.0	0.55 (0.33 to 0.90)	26.0	0.64 (0.44 to 0.93)
P for trend		0.02		0.004
Soluble dietary fibre
Q1 (2.2)	17.1	1.00	32.1	1.00
Q2 (2.8)	12.3	0.69 (0.43 to 1.10)	30.0	0.95 (0.66 to 1.36)
Q3 (3.3)	13.0	0.69 (0.43 to 1.10)	26.3	0.70 (0.48 to 1.01)
Q4 (4.2)	10.0	0.57 (0.34 to 0.94)	28.3	0.85 (0.59 to 1.23)
P for trend		0.03		0.19
Insoluble dietary fibre
Q1 (6.3)	18.7	1.00	35.1	1.00
Q2 (7.7)	11.3	0.57 (0.35 to 0.91)	29.3	0.78 (0.54 to 1.11)
Q3 (9.1)	13.0	0.66 (0.41 to 1.05)	26.3	0.65 (0.45 to 0.93)
Q4 (11.4)	9.3	0.48 (0.29 to 0.80)	26.0	0.63 (0.43 to 0.91)
P for trend		0.009		0.008

^*Quartile medians in g/day adjusted for energy intake using the residual method are given in parentheses.

^†Adjusted for maternal age, gestation at baseline, region of residence at baseline, number of children at baseline, maternal and paternal education, household income, maternal depressive symptoms during pregnancy, maternal alcohol intake during pregnancy, maternal smoking during pregnancy, child’s birth weight, child’s sex, postnatal secondhand smoke exposure at home during the first year of life and breastfeeding duration.

Maternal consumption of soluble dietary fibre during pregnancy was independently inversely associated with the risk of hyperactivity problems in children (adjusted OR between extreme quartiles: 0.57, 95% CI 0.34 to 0.94; p for trend=0.03). Maternal consumption of insoluble dietary fibre during pregnancy was independently associated with both a reduced risk of hyperactivity problems (adjusted OR between extreme quartiles: 0.48, 95% CI 0.29 to 0.80; p for trend=0.009) and a reduced risk of low prosocial behaviour (adjusted OR between extreme quartiles: 0.63, 95% CI 0.43 to 0.91; p for trend=0.008) in children. No significant interactions were observed between maternal consumption of total, soluble, or insoluble dietary fibre and child’s sex regarding childhood hyperactivity problems or low prosocial behaviour.

There were no measurable associations between maternal consumption of total, soluble or insoluble dietary fibre during pregnancy and childhood emotional, conduct or peer problems (table 3).

Table 3. ORs and 95% CIs for emotional, conduct and peer problems assessed by the Strengths and Difficulties Questionnaire in 1199 5-year-old children by quartiles of maternal dietary fibre intake during pregnancy.

	Emotional problems		Conduct problems		Peer problems
Variables*	Risk (%)	Adjusted OR (95% CI)†	Risk (%)	Adjusted OR (95% CI)†	Risk (%)	Adjusted OR (95% CI)†
Total dietary fibre
Q1 (8.8)	14.4	1.00	21.4	1.00	10.4	1.00
Q2 (11.0)	13.0	0.89 (0.54 to 1.44)	20.3	0.99 (0.66 to 1.49)	8.3	0.84 (0.47 to 1.47)
Q3 (13.1)	10.7	0.82 (0.49 to 1.36)	17.7	0.91 (0.59 to 1.39)	8.0	0.88 (0.49 to 1.57)
Q4 (16.2)	13.7	1.15 (0.70 to 1.88)	18.3	1.03 (0.67 to 1.57)	7.7	0.81 (0.44 to 1.46)
P for trend		0.68		0.98		0.52
Soluble dietary fibre
Q1 (2.2)	13.4	1.00	19.7	1.00	9.7	1.00
Q2 (2.8)	13.3	0.97 (0.59 to 1.58)	21.3	1.16 (0.77 to 1.76)	9.3	1.03 (0.59 to 1.82)
Q3 (3.3)	13.0	1.05 (0.64 to 1.73)	18.7	0.97 (0.63 to 1.47)	8.0	0.88 (0.49 to 1.58)
Q4 (4.2)	12.0	1.05 (0.63 to 1.74)	18.0	1.07 (0.70 to 1.65)	7.3	0.84 (0.45 to 1.53)
P for trend		0.78		0.99		0.48
Insoluble dietary fibre
Q1 (6.3)	14.4	1.00	23.1	1.00	10.4	1.00
Q2 (7.7)	14.0	1.00 (0.62 to 1.62)	19.0	0.81 (0.53 to 1.22)	9.0	0.93 (0.53 to 1.63)
Q3 (9.1)	10.7	0.82 (0.49 to 1.37)	17.3	0.80 (0.52 to 1.21)	7.0	0.76 (0.41 to 1.39)
Q4 (11.4)	12.7	1.09 (0.66 to 1.79)	18.3	0.91 (0.60 to 1.38)	8.0	0.87 (0.48 to 1.56)
P for trend		0.94		0.64		0.52

^*Quartile medians in g/day adjusted for energy intake using the residual method are given in parentheses.

^†Adjusted for maternal age, gestation at baseline, region of residence at baseline, number of children at baseline, maternal and paternal education, household income, maternal depressive symptoms during pregnancy, maternal alcohol intake during pregnancy, maternal smoking during pregnancy, child’s birth weight, child’s sex, postnatal secondhand smoke exposure at home during the first year of life and breastfeeding duration.

Discussion

The current prebirth cohort study demonstrated that higher maternal intake levels of total and insoluble dietary fibre intake during pregnancy were independently associated with a reduced risk of childhood hyperactivity problems and low prosocial behaviour, whereas higher maternal soluble fibre intake during pregnancy was independently associated with a reduced risk of childhood hyperactivity problems.

In the Norwegian Mother, Father, and Child Cohort Study of 21 852 mother–father–child trios, which examined the relationship between maternal fibre intake during pregnancy and offspring ADHD symptoms at ages 3, 5 and 8 years, an association was found between higher maternal fibre intake and lower offspring ADHD symptom scores across all ages.³ Similarly, in the Japan Environment and Children Study of 76 207 mother–child pairs, higher maternal total dietary fibre intake during pregnancy was inversely related to developmental delays in communication, gross motor skills, fine motor skills, problem-solving and personal-social skills assessed using the Ages and Stages Questionnaire in children at the age of 3 years.³⁰ Our results are partially consistent with these findings.

The mechanism by which dietary fibre influences the observed association requires further investigation. Previous studies suggest potential pathways through which dietary fibre may exert effects, either via microbiota-independent mechanisms (involving interactions of dietary fibre with enterocytes, macrophages, monocytes and mast cells, or their regulation of cytokine and chemokine production and release, promoting the development of the intestinal immune system) or via microbiota-dependent mechanisms.⁴ A microbiota-dependent mechanism appears particularly relevant to the results observed in this study, as numerous reports have documented the effects of high dietary fibre intake on promoting microbial diversity.⁴ Additionally, maternal gut microbiota has been shown to correlate with neurodevelopment³¹ and behaviour³² in offspring.

This microbiota-dependent mechanism of dietary fibre function is closely linked to SCFAs, which are produced by bacterial fermentation of dietary fibre.^{4 30} A study in mice clearly demonstrates that prepregnancy maternal high-fibre intake improves social and behavioural deficits in offspring by restructuring the gut microbiome. It also protects offspring against synaptic impairment and disruptions in microglia maturation in the hippocampus and prefrontal cortex, underscoring the importance of SCFAs in these processes.⁵

Methodological strengths of the present study include data collection from a relatively large sample over an extended period, spanning from prebirth to 5 years of age, and adjustment for various potential confounding factors.

However, certain limitations should be considered when interpreting the results. Despite adjusting for numerous potential confounding factors, the possibility of residual confounding cannot be entirely dismissed. As for dietary assessment, the DHQ was designed to assess dietary intake for the month preceding completion, providing only approximate consumption data. In addition, participants completed the DHQ between the 5th and 39th week of pregnancy, potentially introducing non-differential exposure misclassification that could attenuate the measures of association. Children were stratified according to whether their mothers participated in the baseline survey by the 17th week of gestation (n=635) or from the 18th week onward (n=564). No clear differences were observed between the two groups in the strength of the associations. For hyperactivity problems, the adjusted ORs (95% CIs; p for trend) for the highest versus lowest quartiles were 0.55 (0.26 to 1.12; 0.08) and 0.48 (0.23 to 1.004; 0.06), respectively. For low prosocial behaviour, the corresponding ORs were 0.55 (0.31 to 0.95; 0.047) and 0.65 (0.39 to 1.09; 0.01).

Regarding the SDQ, the parent-reported data may be subject to bias. Furthermore, while the dichotomisation cut-off points for the five outcomes studied were based on a previous Japanese study,¹⁹ their appropriateness remains uncertain. Non-differential outcome misclassification could have biased the observed associations toward the null hypothesis.

Of the 1757 pregnant women who completed the baseline survey for this study between April 2007 and March 2008, 556 mother–child pairs were excluded because they did not participate in the eighth survey. We observed no significant differences between these 556 non-participants and the 1201 participants in the eighth survey regarding the distribution of the number of children, depressive symptoms during pregnancy or alcohol intake during pregnancy.

Compared with non-participants, participants in the eighth survey were more likely to be older, have participated in the baseline survey earlier in gestation, live in Fukuoka Prefecture, report high maternal and paternal educational levels and have a high household income.

Due to the unidentified distribution numbers of pregnant women who received the leaflet explaining the KOMCHS, an application form, and a set of self-addressed and stamped return envelopes at the 423 collaborating obstetric hospitals, we were unable to calculate the baseline participation rate. Among the 1757 participants at baseline, 978 lived in Fukuoka Prefecture. Data collected by the government of Fukuoka Prefecture revealed that there were 46 393 children born in 2007 and 46 695 children born in 2008, which suggests that the participation rate in the baseline survey of the KOMCHS must have been low. Therefore, the present study participants were probably not representative of Japanese women in the general population.

For instance, according to a population census conducted in 2000 in Fukuoka Prefecture, the proportions of women aged 30–34 years with <13 years, 13–14 years, ≥15 years and an unknown number of years of education were 52.0%, 31.5%, 11.8% and 4.8%, respectively,³³ while the corresponding figures for the present study were 20.9%, 33.3%, 45.9% and 0.0%, respectively. The crude median total fibre intake in the present study was 11.7 g/day. This is comparable to the general population, as the 2007 Japan National Health and Nutrition Survey reported median daily intakes of 11.7 g for women aged 18–29 and 12.3 g for those aged 30–49.³⁴ Therefore, although our study population may be subject to selection bias toward higher socioeconomic status, this bias is unlikely to have substantially affected our findings, as the primary exposure—dietary fibre intake—remained consistent with that of the general population.

Conclusions

Our prebirth cohort study found that a higher maternal intake level of total dietary fibre during pregnancy was independently associated with a decreased risk of hyperactivity problems and low prosocial behaviour in 5-year-old Japanese children. Maternal consumption of soluble dietary fibre was independently inversely associated with the risk of childhood hyperactivity problems, while maternal intake of insoluble dietary fibre was independently inversely associated with the risk of both childhood hyperactivity problems and low prosocial behaviour. We recognise the need for additional epidemiological studies and research investigating the mechanisms that underlie these observed inverse associations.

Data availability statement

No data are available.