Ryukyus Child Health Study Research Articles

An energy-dense diet is cross-sectionally associated with an increased risk of overweight in male children, but not in female children, male adolescents, or female adolescents in Japan: the Ryukyus Child Health Study

Epidemiologic evidence concerning the role of dietary energy density in increased body weight status during childhood and adolescence is limited, particularly in non-Western populations. We investigated the hypothesis that higher dietary energy density is associated with increasing risk of overweight in Japanese children and adolescents. This Japanese cross-sectional study included 15974 children (6-11 years old; 7956 boys and 8018 girls) and 8202 adolescents (12-15 years old; 3944 boys and 4258 girls). Dietary intake was assessed using a self-administered diet history questionnaire for children and adolescents. Dietary energy density was calculated based on foods only (excluding beverages). Body mass index (BMI) was calculated from self-reported body weight and height. Overweight (including obesity) was defined according to the International Obesity Task Force age- and sex-specific BMI cutoffs, which correspond to an adult BMI of at least 25 kg/m². The overall prevalence of overweight was 13.2%. Mean dietary energy density was 5.02 (standard deviation, 0.59) kJ/g. After adjustment for potential confounding factors, dietary energy density was positively associated with the risk of overweight in male children (P for trend = .048). No such associations were observed among female children, male adolescents, or female adolescents. In conclusion, this large cross-sectional study in Japan suggests that an energy-dense diet is associated with an increased risk of overweight in male children, but not in female children, male adolescents, or female adolescents.

Self-Reported Rate of Eating and Risk of Overweight in Japanese Children: Ryukyus Child Health Study

The possible role of eating rate in promoting obesity has long been of interest. We examined the association between rate of eating and overweight status in Japanese children and adolescents. This Japanese cross-sectional study included 15,974 children (6-11 y; 7,956 boys and 8,018 girls) and 8,202 adolescents (12-15 y; 3,944 boys and 4,258 girls). Rate of eating was self-reported according to five categories. Body mass index (BMI) was calculated from self-reported body weight and height. Overweight was defined according to the International Obesity Task Force age- and sex-specific BMI cutoffs. The overall prevalence of overweight was 13.2%. Rate of eating was positively associated with the risk of overweight, independent of protein, fat, and dietary fiber intakes. Multivariate odds ratios (95% confidence intervals) for overweight in the very slow, relatively slow, medium, relatively fast, and very fast categories were 0.31 (0.20, 0.49), 0.49 (0.40, 0.60), 1 (reference), 2.81 (2.42, 3.26), and 4.49 (3.47, 5.81) in male children; 0.42 (0.31, 0.58), 0.49 (0.41, 0.59), 1 (reference), 2.74 (2.27, 3.31), and 5.69 (3.75, 8.63) in female children; 0.13 (0.03, 0.54), 0.43 (0.28, 0.65), 1 (reference), 2.31 (1.88, 2.84), and 3.84 (2.77, 5.31) in male adolescents; and 0.55 (0.30, 1.01), 0.46 (0.33, 0.65), 1 (reference), 1.30 (0.99, 1.71), and 1.49 (0.84, 2.65) in female adolescents, respectively (all p for trend<0.0001). In conclusion, this large cross-sectional study in Japan showed that a higher rate of eating was independently positively associated with an increasing risk of overweight in children and adolescents.

Characteristics of under- and over-reporters of energy intake among Japanese children and adolescents: The Ryukyus Child Health Study

ObjectiveEvidence on factors associated with misreporting of energy intake in children and adolescents is sparse, particularly in non-Western countries. We examined the characteristics of under- and over-reporters of energy intake in Japanese children and adolescents. MethodsThis study included 25 761 Japanese boys and girls 6 to 15 y old. Energy intake was assessed using a self-administered diet history questionnaire developed for Japanese children and adolescents. Estimated energy requirement was calculated from self-reported body weight with the use of equations from the Food and Agriculture Organization (FAO)/World Health Organization (WHO)/United Nations University (UNU) Expert Consultation Report on Human Energy Requirements. Under-reporters, acceptable reporters, and over-reporters of energy intake were identified based on the ratio of energy intake to estimated energy requirement (<0.76, 0.76 to 1.24, and >1.24, respectively). The risk of being an under- or over-reporter of energy intake compared with being an acceptable reporter was analyzed using logistic regression. ResultsThe percentages of under-, acceptable, and over-reporters of energy intake were 31.6%, 53.2%, and 15.2%, respectively. Under-reporting was associated with female sex, older age, overweight and obesity, low parental education, and completion of the dietary questionnaire without the cooperation of parent(s)/caregiver(s). Over-reporting was associated with younger age, normal weight, low parental education, and completion of the dietary questionnaire by the child/adolescent alone (compared with completion by the child/adolescent and parent[s]/caregiver[s]). ConclusionsAlthough under- and over-reporting of energy intake were common and differential in this study of Japanese children and adolescents, the cooperation of parent(s)/caregiver(s) in answering the dietary questionnaire seemed to improve the quality of dietary intake data.

U-Shaped Association between Body Mass Index and the Prevalence of Wheeze and Asthma, but not Eczema or Rhinoconjunctivitis: The Ryukyus Child Health Study

Background. Studies reporting on the association between obesity and allergies have mostly focused on asthma. Little is known about the relationship of obesity to other allergic diseases, and the information that is available has been inconsistent. We examined the association between body mass index (BMI) and the prevalence of wheeze, asthma, eczema, and rhinoconjunctivitis in Japanese schoolchildren. Methods. Study subjects were 24,399 children aged 6–15 years in Okinawa, Japan. Outcomes were based on diagnostic criteria from the International Study of Asthma and Allergies in Childhood. BMI was categorized into five groups; <5th, 5th to 35th, >35th to 65th, >65th to 95th, and >95th percentile groups. Adjustment was made for sex, age, region of residence, number of siblings, smoking in the household, physical activity, paternal and maternal history of allergic disorders, and paternal and maternal educational levels. Results. The prevalence values of wheeze, asthma, eczema, and rhinoconjunctivitis in the previous 12 months were 10.8%, 7.6%, 6.9%, and 7.6%, respectively. Compared with the referent category (>35th to 65th percentile group), higher percentile categories were positively associated with the prevalence of wheeze. A U-shaped relationship between BMI and asthma was observed. No material associations between BMI percentile categories and the prevalence of eczema or rhinoconjunctivitis were found. Conclusion. These findings suggested that being either underweight or overweight might increase the likelihood of asthma among Japanese schoolchildren.

Polyunsaturated fatty acid intake and prevalence of eczema and rhinoconjunctivitis in Japanese children: The Ryukyus Child Health Study

BackgroundThe recent increase in the prevalence of allergic disorders might be a consequence of increased intake of n-6 polyunsaturated fatty acids (PUFAs) and reduced intake of n-3 PUFAs. The current cross-sectional study examined the association between intake levels and the prevalence of eczema and rhinoconjunctivitis in Japanese children.MethodsSubjects were 23,388 schoolchildren aged 6-15 years residing in Okinawa. The presence of eczema and/or rhinoconjunctivitis was determined according to the criteria of the International Study of Asthma and Allergies in Childhood. A brief diet history questionnaire for children and adolescents was administered to acquire information on dietary factors. Adjustment was made for age, sex, residential municipality, number of siblings, smoking in the household, body mass index, paternal and maternal history of allergic diseases, and paternal and maternal educational level.ResultsThe prevalences of eczema and rhinoconjunctivitis in the previous 12 months were 7.0% and 8.0%, respectively. Consumption of PUFAs, n-3 PUFAs, α-linolenic acid, n-6 PUFAs, and linoleic acid was positively associated with the prevalence of eczema: the adjusted odds ratios (ORs) between extreme quintiles (95% confidence intervals [CIs], P for trend) were 1.26 (1.07-1.48, 0.04), 1.31 (1.11-1.54, 0.009), 1.31 (1.12-1.55, 0.003), 1.26 (1.07-1.48, 0.01), and 1.27 (1.08-1.49, 0.01), respectively. Arachidonic acid intake was independently inversely related to eczema: the adjusted OR between extreme quintiles was 0.81 (0.69-0.95, 0.0008). Eczema was not associated with eicosapentaenoic or docosahexaenoic acid intake, or with the ratio of n-3 to n-6 PUFA intake. Only arachidonic acid intake was statistically significantly related to the prevalence of rhinoconjunctivitis, showing a clear inverse linear trend: the adjusted OR between extreme quintiles was 0.86 (0.74-0.997, 0.03).ConclusionsConsumption of n-3 and n-6 PUFAs, especially α-linolenic acid and linoleic acid, may be positively associated with eczema. Arachidonic acid intake may be inversely related to eczema and rhinoconjunctivitis.

Dietary glycemic index and glycemic load in relation to risk of overweight in Japanese children and adolescents: the Ryukyus Child Health Study

Epidemiologic evidence concerning the role of dietary glycemic index (GI) and glycemic load (GL) in obesity during childhood and adolescence is limited, particularly in non-Western populations. We examined the association between dietary GI and GL as well as dietary fiber intake and overweight status in Japanese children and adolescents. This Japanese cross-sectional study included 15,974 children (6-11 years; 7956 boys and 8018 girls) and 8202 adolescents (12-15 years; 3944 boys and 4258 girls). Dietary intake was assessed using a self-administered diet history questionnaire for children and adolescents. Body mass index (BMI) was calculated from self-reported body weight and height. Overweight was defined according to the International Obesity Task Force age- and sex-specific BMI cutoffs, which correspond to an adult BMI of 25 kg m(-2). The overall prevalence of overweight was 13.2%. Mean (s.d.) dietary GI was 63.0 (3.1), mean dietary GL was 85.0 (12.4) per 4184 kJ (1000 kcal) and mean dietary fiber intake was 5.9 (1.2) g/4184 kJ. After adjustment for potential confounding factors, dietary GL was positively associated with the risk of overweight in male children, female children and male adolescents (P for trend <0.0001, <0.0001 and 0.006, respectively), but not in female adolescents. No such independent associations were observed for dietary GI or fiber intake. This large cross-sectional study in Japan suggests that higher dietary GL is associated with increasing risk of overweight in male and female children and male adolescents, but not female adolescents.

Fish and n-3 Polyunsaturated Fatty Acid Intake and Depressive Symptoms: Ryukyus Child Health Study

Epidemiologic evidence on the role of fish and long-chain n-3 polyunsaturated fatty acid intake on depression during adolescence is sparse. We examined the association between fish, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) intake and depressive symptoms in a group of adolescents. This cross-sectional study, conducted in all public junior high schools in Naha City and Nago City, Okinawa, Japan, included 3067 boys and 3450 girls aged 12 to 15 years (52.3% of the eligible sample). Dietary intake was assessed by using a validated, self-administered diet-history questionnaire. Depressive symptoms were defined as present when participants had a Center for Epidemiologic Studies Depression scale score of >or=16. The prevalence of depressive symptoms was 22.5% for boys and 31.2% for girls. For boys, fish intake was inversely associated with depressive symptoms (adjusted odds ratio [OR] for depressive symptoms in the highest [compared with the lowest] quintile of intake: 0.73 [95% confidence interval (CI): 0.55-0.97]; P for trend=.04). EPA intake showed an inverse association with depressive symptoms (OR: 0.71 [95% CI: 0.54-0.94]; P=.04). DHA intake also showed a similar inverse, albeit nonsignificant, association (OR: 0.79 [95% CI: 0.59-1.05]; P=.11). In addition, intake of EPA plus DHA was inversely associated with depressive symptoms (OR: 0.72 [95% CI: 0.55-0.96]; P=.08). Conversely, no such associations were observed among girls. Higher intake of fish, EPA, and DHA was independently associated with a lower prevalence of depressive symptoms in early male, but not female, adolescents.

Dietary Folate, Riboflavin, Vitamin B-6, and Vitamin B-12 and Depressive Symptoms in Early Adolescence: The Ryukyus Child Health Study

To examine the association between dietary folate, riboflavin, vitamin B-6, and vitamin B-12 and depressive symptoms in a group of adolescents. This cross-sectional study, conducted in all public junior high schools in Naha City and Nago City, Okinawa, Japan, included 3,067 boys and 3,450 girls aged 12 years to 15 years (52.3% of eligible sample). Dietary intake was assessed using a validated, self-administered diet history questionnaire. Depressive symptoms were defined as present when participants had a Center for Epidemiologic Studies Depression Scale score of ≥16. The prevalence of depressive symptoms was 22.5% for boys and 31.2% for girls. Folate intake was inversely associated with depressive symptoms in both boys (adjusted odds ratio (OR) [95% confidence interval (CI)] in the highest (compared with the lowest) quintile, 0.60 [0.45, 0.79]; p for trend = .002) and girls (OR [95% CI], 0.61 [0.48, 0.77]; p for trend = <.001). Vitamin B-6 intake was inversely associated with depressive symptoms in both boys (OR [95% CI], 0.73 [0.54, 0.98]; p for trend = .02) and girls (OR [95% CI], 0.72 [0.56, 0.92]; p for trend = .002). Riboflavin intake was inversely associated with depressive symptoms in girls (OR [95% CI], 0.85 [0.67, 1.08]; p for trend = .03), but not in boys. No clear association was seen between vitamin B-12 intake and depressive symptoms in either sex. This study suggests that higher intake of dietary B vitamins, particularly folate and vitamin B-6, is independently associated with a lower prevalence of depressive symptoms in early adolescence.

Household smoking and dental caries in schoolchildren: the Ryukyus Child Health Study

BackgroundSecondhand smoke exposure (SHSe) is perhaps one of the most important toxic exposures in childhood. However, epidemiological studies on the relation between SHSe and dental caries are limited and have yielded inconsistent results. The present cross-sectional study examined the potential association between SHSe at home and the prevalence of dental caries in children.MethodsSubjects were 20,703 schoolchildren aged 6 to 15 years in Okinawa, Japan. Information on SHSe at home and potential confounding factors was obtained through questionnaires. Data on dental caries were obtained from school records. Children were classified as having decayed and/or filled teeth (DFT) if a dentist diagnosed these conditions. Additionally, we analyzed decayed teeth (DT) and filled teeth (FT) separately. Adjustment was made for sex, age, region of residence, toothbrushing frequency, use of fluoride, sugar intake, and paternal and maternal educational level.ResultsThe prevalence of DFT was 82.0%. Compared with never smoking in the household, former and current household smoking were independently associated with an increased prevalence of DFT (adjusted prevalence ratios [95% confidence intervals] for former household smoking and current light and heavy household smoking were 1.03 [1.00-1.05], 1.04 [1.02-1.05], and 1.04 [1.03-1.06], respectively); when analyzed separately there was an increased prevalence of DT (adjusted prevalence ratios [95% confidence intervals] for former household smoking and current light and heavy household smoking were 1.06 [1.02-1.11], 1.10 [1.06-1.13], and 1.10 [1.07-1.14], respectively) but not FT. A statistically significant dose-response relationship between cumulative smoking in the household and the prevalence of DFT and DT (P for trend < 0.0001), but not FT, was observed. In an analysis of 2 subgroups, subjects who had at least 1 deciduous tooth and subjects who had at least 1 permanent tooth, household smoking exposure was associated with an increased prevalence of DFT and DT not only in those with deciduous but also those with permanent dentition.ConclusionOur findings suggested that household smoking might be associated with an increased prevalence of dental caries in children.

Sibship size and prevalence of allergic disorders in Japan: The Ryukyus Child Health Study

A number of epidemiological studies have reported an inverse association between increasing sibship size and allergic disorders. The present cross-sectional study assessed the association between the number of siblings and the prevalence of allergic disorders during the past 12 months in Japanese schoolchildren. Study subjects were 22,750 children aged 6-15 yr in Okinawa. The outcomes were based on diagnostic criteria from the International Study of Asthma and Allergies in Childhood. Adjustment was made for age, gender, maternal age at childbirth, duration of breastfeeding, region of residence, smoking in the household, paternal and maternal history of asthma, atopic eczema, and allergic rhinitis, and paternal and maternal educational level. Significant exposure-response associations were observed between increasing total sibship size and all outcomes under investigation. Having two or more older siblings was significantly inversely related to the prevalence of atopic eczema and allergic rhinoconjunctivitis, but not wheeze or asthma. Having two or more younger siblings was independently associated with a decreased prevalence of atopic eczema, but not wheeze, asthma, or allergic rhinoconjunctivitis. The inverse relationships between sibship size and the prevalence of allergic disorders under study were weakened with advancing age, although the interactions between age groups were not statistically significant. No significant interactions were found in the association of having three or more siblings with allergic disorders between children with a positive or negative parental allergic history. These results are likely to support the in utero programming hypothesis because it is probable that the in utero environment would change with parity, although our observations could not refute the hygiene hypothesis.

Fatty acid intake and asthma symptoms in Japanese children: The Ryukyus Child Health Study

It has been hypothesized that increased consumption of n-6 polyunsaturated fatty acids and decreased consumption of n-3 polyunsaturated fatty acids have contributed to the recent increased prevalence of asthma. The present cross-sectional study examined the association of intake of specific types of fatty acids with the prevalence of asthma symptoms using data from the Ryukyus Child Health Study. Study subjects were 25,033 schoolchildren aged 6-15 years in Okinawa, Japan. Symptoms of wheeze and asthma were defined according to diagnostic criteria from the International Study of Asthma and Allergies in Childhood. Information on dietary factors was collected using a self-administered brief diet history questionnaire for children. Adjustment was made for age, sex, number of siblings, smoking in the household, body mass index, paternal and maternal history of allergic diseases, and paternal and maternal educational level. Intake of polyunsaturated fatty acids, n-3 and n-6 polyunsaturated fatty acids and linoleic acid (18:2 n-6) was independently associated with an increased prevalence of wheeze--the multivariate odds ratios for the highest quintile were 1.19 (95% confidence interval [CI], 1.05-1.35), 1.17 (95% CI, 1.03-1.34), 1.19 (95% CI, 1.04-1.35), and 1.20 (95% CI, 1.06-1.37), respectively. There was no measurable relationship of consumption of alpha-linolenic (18:3 n-3), eicosapentaenoic (20:5 n-3), docosahexaenoic (22:6 n-3) or arachidonic acid (20:4 n-6) or the ratio of n-3 to n-6 polyunsaturated fatty acids with the prevalence of wheeze. Consumption of total fat, saturated fatty acids, monounsaturated fatty acids and cholesterol were not evidently related to wheeze. No material dose-response association was found between the intake of any of the types of fatty acids considered and the prevalence of asthma. The findings suggest that consumption of both n-3 and n-6 polyunsaturated fatty acids, especially linoleic acid, may be associated with an increased prevalence of wheeze.

Dental Caries and Allergic Disorders in Japanese Children: The Ryukyus Child Health Study

Background. Dental caries is an infectious disease and is highly prevalent among children. In the etiology of allergic diseases, the hygiene hypothesis contends that infections might confer protection against the development of allergic diseases. The aim of this cross-sectional study was to investigate the association between dental caries and the prevalence of allergic disorders. Methods. Study subjects were 21,792 children 6 to 15 years of age in Okinawa, Japan. Outcomes were based on diagnostic criteria from the International Study of Asthma and Allergies in Childhood. Data on dental caries were obtained from school records. Children were classified as having dental caries if one or more teeth had decayed and/or had been filled. Adjustment was made for sex, age, region of residence, number of siblings, smoking in the household, paternal and maternal history of asthma, atopic eczema, or allergic rhinitis, and paternal and maternal educational level. Results. The prevalence of wheeze, asthma, atopic eczema, and allergic rhinoconjunctivitis in the previous 12 months was 10.8%, 7.6%, 6.8%, and 7.6%, respectively. In an overall analysis, no measurable relationship was found between dental caries and the prevalence of wheeze, asthma, atopic eczema, or allergic rhinoconjunctivitis. However, dental caries was significantly inversely associated with the prevalence of allergic rhinoconjunctivitis only among children with a positive parental allergic history: The adjusted odds ratio was 0.84 (95% confidence interval: 0.72, 0.99). Conclusions. The present findings do not support the hypothesis that dental caries was protective against allergic diseases. However, a parental allergic history may affect the association between dental caries and allergic rhinoconjunctivitis.

Tuberculin reactivity and allergic disorders in schoolchildren, Okinawa, Japan

Bacillus Calmette-Guérin (BCG) vaccination triggers a T-helper type 1 response. Whether BCG vaccination and positive tuberculin reactivity are preventive against allergic disorders remains controversial. The current cross-sectional study investigated the relationship of BCG vaccination and tuberculin reactivity with the prevalence of allergic disorders using data from the Ryukyus Child Health Study (RYUCHS). Subjects were 5717 schoolchildren aged 8-11 years in Okinawa, Japan. The RYUCHS collected information on symptoms of allergic disorders and potential confounding factors. The outcomes were based on diagnostic criteria from the International Study of Asthma and Allergies in Childhood. Data on BCG vaccination and tuberculin tests were obtained from school records. Allowance was made for grade, sex, sibship size, smoking in the household, paternal and maternal history of asthma, atopic eczema, and allergic rhinitis, and paternal and maternal educational level. No measurable relationship was found between BCG vaccination in infants and the prevalence of allergic disorders. Among 5567 BCG-vaccinated children, positive tuberculin reactivity (induration >/=10 mm) in the first grade was independently associated with a decreased prevalence of wheeze, asthma, and atopic eczema: the multivariate odds ratios for wheeze, asthma, and atopic eczema were 0.80 (95% confidence interval [CI], 0.67-0.94), 0.78 (95% CI, 0.64-0.95), and 0.77 (95% CI, 0.62-0.95), respectively. The inverse associations were more pronounced in children with a negative parental allergic history than in those with a positive parental allergic history. There was no significant relationship between tuberculin reactivity and allergic rhinoconjunctivitis. The findings suggest that positive tuberculin reactivity may be inversely associated with the prevalence of wheeze, asthma, and atopic eczema, but not allergic rhinoconjunctivitis, especially among Japanese children without a parental allergic history.

Cross‐sectional study of allergic disorders associated with breastfeeding in Japan: The Ryukyus Child Health Study

Uncertainties remain as to whether breastfeeding is protective against childhood allergic disorders. Positive relationships of breastfeeding with asthma and atopic eczema were observed in two previous Japanese studies. This cross-sectional study investigated the association between the feeding pattern after birth and the prevalence of allergic disorders during the past 12 months in Japanese schoolchildren. Study subjects were 24,077 children aged 6-15 yr in Okinawa. The outcomes were based on diagnostic criteria from the International Study of Asthma and Allergies in Childhood. Allowance was made for age, sex, number of siblings, smoking in the household, paternal and maternal history of asthma, atopic eczema, and allergic rhinitis, and paternal and maternal educational level. Breastfeeding, regardless of exclusivity, for 13 months or longer and exclusive breastfeeding for 4-11 months were independently associated with a higher prevalence of atopic eczema, particularly among children without a parental allergic history. A clear positive dose-response relationship was observed between prolonged duration of breastfeeding, regardless of exclusivity, but not exclusive breastfeeding, and the prevalence of atopic eczema. We found a significant positive trend for atopic eczema across the three categories (formula milk, partial and exclusive breastfeeding) in the first 4 months of life although the odds ratio for exclusive breastfeeding was not statistically significant. No material association was found between the feeding pattern after birth and the prevalence of wheeze or allergic rhinoconjunctivitis. Prolonged breastfeeding may be associated with a higher prevalence of atopic eczema in Japanese children.