[Impact of iron deficiency in early life stages on children's motor development: a longitudinal follow-up].

Objective: To clarify the impact of pre- and postnatal iron deficiency on children's motor development. Methods: This was a longitudinal follow-up study. A total of 114 infants (58 boys, 56 girls) born from April 2010 to December 2011 in Fuyang district of Hangzhou were enrolled. Based on cord blood and 9-month iron status, subjects were divided into prenatal iron deficiency (34 children), postnatal iron deficiency (37 children) and non-iron deficiency group (43 children). Peabody Developmental Motor Scale and BOT2-simplified version were used to evaluate the motor capacity in infants and preschoolers at 9 months, 18 months and 5 years, respectively. Hierarchical linear modeling (HLM) was used to investigate the trajectory of motor development with age, the influence of different timing of early iron deficiency on children's motor development, and the differences (adjusted for possible confounding factors) in motor development in children with pre- or postnatal iron deficiency or non-iron deficiency in different family educational environment. Results: At the age of 9 months, 18 months and 5 years, 107, 109, and 114 children were evaluated respectively. After controlling for a variety of confounding factors, it was found that children with prenatal iron deficiency had significantly lower scores of motor development compared with non-iron deficiency children (52.04 vs. 54.05 scores, ß=-2.01, P=0.007), and that children with postnatal iron deficiency had similar scores of motor development compared with non-iron deficiency children, showing no significant difference (53.07 vs. 54.05 scores, ß=-0.98, P=0.180). Regardless of the maternal education status, prenatal iron deficiency children always had lower motor scores than non-iron deficiency children (49.86 vs. 52.15 and 49.58 vs. 51.58 scores, ß=-2.29, -2.00; P=0.031, 0.049). Among the non-iron deficiency children, those whose mothers had a higher education level had higher motor scores compared with those whose mothers had a lower education level (52.45 vs. 50.46 scores, ß=1.99, P=0.035). Conclusions: The motor development of children with prenatal iron deficiency did not catch up with their counterparts without iron deficiency by 5 years of age. The results indicate the importance of preventing iron deficiency in the fetus.

Ferritin levels throughout childhood and metabolic syndrome in adolescent stage.

BACKGROUND AND AIM: Increased ferritin levels have been widely associated with cardiovascular risk in adults. Whether ferritin levels and their changes during childhood are related to metabolic syndrome (MetS) at adolescence is unknown. We aimed to evaluate these associations using levels of ferritin at 5, 10 and 16 years and their linear increases and patterns of sustained increased levels across childhood. METHODS AND RESULTS: There were four samples evaluated according to non-missing values for study variables at each stage (5 years: 562; 10 years: 381; and 16 years: 567 children; non-missing values at any stage: 379). MetS risk was evaluated as a continuous Z score. Patterns of sustained increased ferritin (highest tertile) and slope of the change of ferritin per year across the follow-up were calculated. Ferritin levels in the highest versus lowest tertile at five and 16 years were significantly positively associated with MetS risk Z score at adolescence in boys and these associations were unaffected by adjustment for covariates. Having high, compared to low/moderate ferritin level at 2 or more time periods between 5 and 16 years was related to higher Mets Z-score in boys only [e.g. 5-10 years adjusted-beta (95 %CI):0.26 (0.05-0.48),P < 0.05]. In girls, ferritin Z score at 10 and 16 years was positively and independently associated with HOMA-IR Z score. In girls, the slope of ferritin per year in the highest tertile was positively associated with MetS risk Z-score [adjusted-beta (95 %CI):0.21 (0.05-0.38),P < 0.05]. CONCLUSIONS: Ferritin levels throughout childhood are positively related to cardiometabolic risk in adolescence, with associations varying by sex.

Genetic determinants of BMI from early childhood to adolescence: the Santiago Longitudinal Study.

BACKGROUND: While the genetic contribution to obesity is well established, few studies have examined how genetic variants influence standardized body mass index Z-score (BMIz) in Hispanics/Latinos, especially across childhood and adolescence. OBJECTIVES: We estimated the effect of established BMIz loci in Chilean children of the Santiago Longitudinal Study (SLS). METHODS: We examined associations with BMIz at age 10 for 15 loci previously identified in European children. For significant loci, we performed association analyses at ages 5 and 16 years, for which we have smaller sample sizes. We tested associations of unweighted genetic risk scores (GRSs) for previously identified tag variants (GRS_EUR) and from the most significant variants in SLS at each locus (GRS_SLS). RESULTS: We generalized five variants at age 10 (P < 0.05 and directionally consistent), including rs543874 that reached Bonferroni-corrected significance. The effect on BMIz was greatest at age 10 for all significant loci, except FTO, which exhibited an increase in effect from ages 5 to 16. Both GRSs were associated with BMIz (P < 0.0001), but GRS_SLS explained a much greater proportion of the variation (13.63%). CONCLUSION: Our results underscore the importance of conducting genetic investigations across life stages and selecting ancestry appropriate tag variants in future studies for disease prediction and clinical evaluation.

Greater early weight gain and shorter breastfeeding are associated with low adolescent adiponectin levels.

BACKGROUND: Early life factors can programme future risk for cardiovascular disease. OBJECTIVES: We explored associations between adolescent adiponectin levels and concomitant metabolic alteration and also looked at the association between early life factors and adolescent adiponectin levels. METHODS: We studied a longitudinal cohort of low-income to middle-income Chilean adolescents who were enroled in an infancy iron-deficiency anaemia preventive trial and follow-up studies at the Institute of Nutrition and Food Technology, University of Chile, Santiago, Chile. In the 577 adolescents who were assessed as part of the 16-year follow-up, we evaluated independent associations between adiponectin levels and metabolic disturbances during adolescence. We also assessed the association between early life factors [short breastfeeding {<6 months} and infancy weight gain] and adolescent adiponectin levels. RESULTS: Participants were 16.8 years old (16.4-18.1), 48% female and 38% overweight/obese. Adolescent adiponectin levels were inversely associated with metabolic disturbances: altered homeostatic model assessment of insulin resistance and high-density lipoprotein cholesterol [odds ratios {95% confidence interval} = 0.87 {0.79-0.95}, p-value = 0.002, and 0.90 {0.87-0.94}, p-value < 0.001, respectively], adjusting for sex and fat mass index. Early life factors were independently associated with adolescent adiponectin levels, which decreased 0.88 ug mL-1 per each unit increase in weight-for-age z-score between 0 and 6 months and was 1.58 ug mL-1 lower among participants with short breastfeeding. CONCLUSIONS: Higher adolescent adiponectin levels were independently associated with lower odds of metabolic disturbances. Greater weight gain during infancy and shorter breastfeeding were associated with lower adolescent adiponectin levels, supporting research indicating early life as a window of opportunity for prevention of later cardiovascular alterations. © 2017 World Obesity Federation.

Breastfeeding as the sole source of milk for 6 months and adolescent bone mineral density.

Little is known regarding the relationship between early life factors and bone mineral density (BMD). We found a positive association between breastfeeding for at least 6 months, without formula supplementation, and whole body adolescent BMD z-score. INTRODUCTION: The aim of the study is to assess the role of breastfeeding BF on adolescent bone mineral density (BMD) in a cohort prospectively followed since infancy. METHODS: We studied 679 participants from an infancy iron deficiency anemia preventive trial in Santiago, Chile, followed to adolescence. Breast and bottle feeding were ascertained weekly from 4 to 12 months. At 16 years, whole body BMD was assessed by DEXA. Using linear regression, we evaluated associations between BF duration and BF as the sole source of milk and adolescent BMD z-score, adjusting for possible infancy, adolescent, and background confounders. RESULTS: Mean birth weight and length were 3.5 (0.3) kg and 50.7 (1.6) cm. For at least 6 months, BF was the sole source of milk for 26.3% and with supplementation for 36.7%. For 37%, BF was provided for less than 6 months. Mean 16-year BMD z-score was 0.25 (1.0). Covariates included male sex, birth length, and gestational age. BF as the sole source of milk ≥6 months, compared to BF < 6 months, was associated with higher adolescent BMD z-score adjusting for covariates (ß = 0.29, p < 0.05). Mixed BF was not significantly related to adolescent BMD z-score (ß = 0.06, p = 0.47). For every 30 days of BF as the sole source of milk, adolescent BMD z-score increased by 0.03 (p = 0.01). CONCLUSION: BF without formula supplementation for at least 6 months was associated with higher adolescent BMD z-score and a suggestive trend in the same direction for BMD suggests that exclusivity and duration of BF may play a role in adolescent bone health.

Obesity leads to declines in motor skills across childhood.

BACKGROUND: Poor motor skills have been consistently linked with a higher body weight in childhood, but the causal direction of this association is not fully understood. This study investigated the temporal ordering between children's motor skills and weight status at 5 and 10 years. METHODS: Participants were 668 children (54% male) who were studied from infancy as part of an iron deficiency anaemia preventive trial and follow-up study in Santiago, Chile. All were healthy, full-term and weighing 3 kg or more at birth. Cross-lagged panel modelling was conducted to understand the temporal precedence between children's weight status and motor proficiency. Analyses also examined differences in gross and fine motor skills among healthy weight, overweight, and obese children. RESULTS: A higher BMI at 5 years contributed to declines in motor proficiency from 5 to 10 years. There was no support for the reverse, that is, poor motor skills at 5 years did not predict increases in relative weight from 5 to 10 years. Obesity at 5 years also predicted declines in motor proficiency. When compared with normal weight children, obese children had significantly poorer total and gross motor skills at both 5 and 10 years. Overweight children had poorer total and gross motor skills at 10 years only. The differences in total and gross motor skills among normal weight, overweight and obese children appear to increase with age. There were small differences in fine motor skill between obese and non-obese children at 5 years only. CONCLUSIONS: Obesity preceded declines in motor skills and not the reverse. Study findings suggest that early childhood obesity intervention efforts might help prevent declines in motor proficiency that, in turn, may positively impact children's physical activity and overall fitness levels.

Maternal obesity during pregnancy is negatively associated with maternal and neonatal iron status.

BACKGROUND/OBJECTIVES: Obesity among pregnant women may adversely affect both maternal iron status throughout pregnancy and placental transfer of iron. The objective of this study was to determine the association of maternal body mass index (BMI) with (1) maternal iron status and inflammation in mid and late pregnancy, (2) the change in maternal iron status throughout pregnancy and (3) neonatal iron status. SUBJECTS/METHODS: We examined longitudinal data from 1613 participants in a pregnancy iron supplementation trial in rural China. Women with uncomplicated singleton pregnancies were enrolled in the early second trimester of pregnancy and followed through parturition. Maternal blood samples obtained at enrollment and in the third trimester and cord blood samples were analyzed for a range of hematological and iron biomarkers. RESULTS: There was a negative association between maternal BMI and iron status at enrollment (transferrin receptor (sTfR): r=0.20, P<0.001; body iron (BI): r=-0.05; P=0.03). This association was markedly stronger among obese women. Maternal BMI was positively associated with maternal inflammation (C-reactive protein: r=0.33, P<0.001). In multiple linear regression models, maternal BMI was negatively associated with neonatal iron status (cord serum ferritin: -0.01, P=0.008; BI: -0.06, P=0.006) and associated with a lower decrease in iron status throughout pregnancy (sTfR: -4.6, P<0.001; BI: 1.1, P=0.004). CONCLUSIONS: Maternal obesity during pregnancy may adversely affect both maternal and neonatal iron status, potentially through inflammatory pathways.

Prenatal Iron Deficiency and Auditory Brainstem Responses at 3 and 10 Months: A Pilot Study.

PURPOSE: To examine whether prenatal iron deficiency delays auditory brainstem response (ABR) maturation in infancy. METHODS: One hundred and fifteen full-term healthy Chinese infants with maternal and cord blood haemoglobin and serum ferritin determinations were recruited into this study. Forty-eight infants received ABR testing at 3 months, and 45 infants were tested at 10 months. Comparison of the ABR variables were made between infants with and those without evidence of prenatal iron deficiency (maternal 3rd trimester haemoglobin <110 g/L, cord blood ferritin <75 µg/L); or anaemia at 10 months (haemoglobin <110 g/L). RESULTS: Latencies for wave V and wave III-V and I-V intervals were prolonged at 3 months in infants of anaemic mothers (effect sizes 1.02-1.19 SD). At 10 months, infants with low cord blood serum ferritin (indicating low iron stores at birth) showed longer wave I latency and possibly wave V latency also, besides demonstrating a smaller wave V amplitude (effect sizes 0.58-0.62 SD). Infants with low ferritin at birth and anemia at 10 months had longer wave III-V latency than other groups. CONCLUSION: In full-term healthy infants, prenatal iron deficiency appears to have adverse effects on the developing central nervous system and auditory system as assessed by ABRs at 3 and/or 10 months.

Inhibitory control in otherwise healthy overweight 10-year-old children.

BACKGROUND: Preventing obesity is a worldwide public health priority. In vulnerable children living in obesogenic environments, with easy access to high-caloric food, alterations in inhibitory control functions might favor excessive food intake and affect energy regulation. We hypothesized that overweight/obese children would present lower inhibitory control in comparison to normal weight children. METHODS: We measured inhibitory control functions in 93 otherwise healthy overweight/obese and 92 normal weight 10-year-old children using the Stroop test and the Go/No-Go task. Event-related potentials were recorded during the Go/No-Go task. RESULTS: Overweight/obese children showed slower reaction times (1248.6 ms (95% confidence interval (CI): 1182.9-1314.3) vs 1149.0 ms (95% CI: 1083.0-1215.1)) on the Stroop test, higher reaction time variability (0.25 (95% CI: 0.22-0.27) vs 0.21 (95% CI: 0.19-0.24)) on the Go/No-Go task and decreased P300 amplitude (4.1 µV (95% CI: 3.0-5.2) vs 6.4 µV (95% CI: 5.2-7.6)) on event-related potentials compared with normal weight children. CONCLUSIONS: Our results indicate altered inhibitory control functions in otherwise healthy overweight/obese children, which might contribute to their excessive food consumption.

Satiety responsiveness and eating behavior among Chilean adolescents and the role of breastfeeding.

OBJECTIVE: To determine patterns of satiety responsiveness and its relationship to eating in the absence of hunger (EAH), in a cohort of adolescents. We also assessed whether sex, body mass index and duration of breastfeeding, during infancy, predicted satiety responsiveness and eating behavior at 16 years. METHODS: Adolescents (n=576) from a longitudinal cohort, which began as an iron deficiency anemia preventive trial, participated in an unlimited breakfast after an overnight fast, and reported satiety response on a visual analog scale after the meal, followed by an EAH procedure. Height, weight and body composition were measured before breakfast. Latent profile analysis generated profiles that captured individual differences in satiety responsiveness. Multivariable regressions, adjusted for potential confounders, evaluated the association between: (1) satiety responsiveness and EAH, and (2) breastfeeding in infancy, satiety responsiveness and EAH in adolescence. RESULTS: Participants were on average 16.7-year old, 48% female, 37% overweight/obese and 76% were breastfed as the sole source of milk for <6 months. We found three latent profiles of satiety responsiveness: 1: 'responsive' (49%); 2: 'not responsive' (41%); 3: 'still hungry' (10%). Participants in the 'not responsive' or 'still hungry' profile were more likely to eat during the EAH procedure (odds ratio (OR)=2.5, 95% confidence interval (CI)=1.8-3.6). Being breastfed for <6 months was related to higher odds of being in the 'not responsive' or 'still hungry' profile (OR=1.8, 95% CI=1.2-2.6) and EAH (OR=2.2, 95% CI=1.4-3.3). Satiety responsiveness was not influenced by sex and overweight/obesity. CONCLUSION: After an ad libitum meal, we found varied satiety responses, which related to EAH. Furthermore, shorter breastfeeding duration was associated with poorer satiety response and higher consumption during an EAH procedure. Understanding if breastfeeding influences the development of satiety responsiveness and eating behavior may be important in an era characterized by abundant calorie-dense foods and a plethora of environmental cues promoting consumption.

Night time sleep macrostructure is altered in otherwise healthy 10-year-old overweight children.

OBJECTIVE: Epidemiological evidence shows an inverse relationship between sleep duration and overweight/obesity risk. However, there are few polysomnographic studies that relate the organization of sleep stages to pediatric overweight (OW). We compared sleep organization in otherwise healthy OW and normal-weight (NW) 10-year-old children. SUBJECTS: Polysomnographic assessments were performed in 37 NW and 59 OW children drawn from a longitudinal study beginning in infancy. Weight and height were used to evaluate body mass index (BMI) according to international criteria. Non-rapid eye movement (NREM) sleep (stages N1, N2 and N3), rapid eye movement (REM) sleep (stage R) and wakefulness (stage W) were visually scored. Sleep parameters were compared in NW and OW groups for the whole sleep period time (SPT) and for each successive third of it using independent Student's t-tests or nonparametric tests. The relationship between BMI and sleep variables was evaluated by correlation analyses controlling for relevant covariates. RESULTS: The groups were similar in timing of sleep onset and offset, and sleep period time. BMI was inversely related to total sleep time (TST) and sleep efficiency. OW children showed reduced TST, sleep efficiency and stage R amount, but higher stage W amount. In analysis by thirds of the SPT, the duration of stage N3 episodes was shorter in the first third and longer in the second third in OW children as compared with NW children. CONCLUSIONS: Our results show reduced sleep amount and quality in otherwise healthy OW children. The lower stage R amount and changes involving stage N3 throughout the night suggest that OW in childhood is associated with modifications not only in sleep duration, but also in the ongoing night time patterns of NREM sleep and REM sleep stages.

Motor activity and intra-individual variability according to sleep-wake states in preschool-aged children with iron-deficiency anemia in infancy.

BACKGROUND: A chronic or acute insult may affect the regulatory processes that guide motor and behavioral performance, leading to increased intra-individual variability (IIV). Increased variability is often interpreted as an indication of regulatory dysfunction. Iron plays an important role in the regulatory processes of the nervous system and affects motor activity. To our knowledge, no study has examined the long-lasting patterns and IIV of motor activity following iron-deficiency anemia in human infants. AIMS: This study compared 48-h motor activity and variability in preschool-aged children with or without iron-deficiency anemia (IDA) in infancy. METHODS: Motor activity was recorded through actigraphs during two week-days in 47 4-year-old Chilean children (23 former IDA and 24 non-anemic in infancy). All were given oral iron as infants. Sleep-wake states were identified by means of automated software. The frequency of movement units per minute was determined for each waking/sleep state during the individual day and night periods; data were examined in blocks of 15 min. Analyses of mean frequency and duration and intra-individual variability were conducted using multivariate mixed models. RESULTS: For daytime sleep, former IDA children were more active without a difference in the total duration. They also spent less time awake throughout the individual day period. Motor activity intra-individual variability was higher in former IDA children. CONCLUSIONS: The findings suggest that IDA in infancy sets the stage for long lasting dysfunction in the neural processes regulating sleep-wake states and spontaneous motor activity patterns.

Postnatal Growth Patterns in a Chilean Cohort: The Role of SES and Family Environment.

Objective. This study examined how family environmental characteristics served as mediators in the relationship between socioeconomic conditions and infant growth in a cohort of Chilean infants. Methods. We studied 999 infants, born between 1991 and 1996, from a longitudinal cohort which began as an iron deficiency anemia preventive trial. SES (Graffar Index), the Life Experiences Survey, and the Home Observation for Measurement of the Environment (HOME) were assessed in infancy. Using path analysis, we assessed the relationships between the social factors, home environment, and infant growth. Results. During the first year, weight and length gain averaged 540 grams/month and 6.5 cm/month, respectively. In the path analysis model for weight gain, higher SES and a better physical environment were positively related to higher maternal warmth, which in turn was associated with higher average weight gain. Higher SES was directly related to higher average length gain. Conclusions. In our cohort, a direct relationship between SES and length gain developed during infancy. Higher SES was indirectly related to infant weight gain through the home environment and maternal warmth. As the fastest growing infants are at risk for later obesity, new strategies are needed to encourage optimal rather than maximal growth.

[Conclusions and recommendations of a WHO expert consultation meeting on iron supplementation for infants and young children in malaria endemic areas]. / Conclusions et recommandations à l'issue de la consultation de l'OMS sur la lutte contre la carence martiale chez le nourrisson et le jeune enfant dans les pays d'endémie palustre.

This article presents the results of an expert consultation meeting aimed at evaluating the safety and public health implications of administering supplemental iron to infants and young children in malaria-endemic areas. Participants at this meeting that took place in Lyon, France on June 12-14, 2006 reached consensus on several important issues related to iron supplementation for infants and young children in malaria-endemic areas. The conclusions in this report apply specifically to regions where malaria is endemic.

Twenty-four-hour motor activity in human infants with and without iron deficiency anemia.

Iron deficiency anemia (IDA) is a very common nutritional problem that alters motor activity. The aim of this study was to compare 24-h motor activity in the home in healthy 6-month-old infants with and without IDA. Activity was assessed via actigraphs on the leg during 24 continuous hours in 17 Chilean infants with IDA and 18 with normal hemoglobin levels. All infants were given oral iron, and activity was reassessed at 12 and 18 months. The frequency of movement units per minute was determined for each waking/sleep state during the day and night, and the duration of each state was computed. At 6 months of age, there were no differences between anemic and nonanemic infants in time per state. However, infants with IDA showed an overall increase in motor activity compared to controls. These differences were no longer observed at 12 and 18 months of age. Increased activity during the period of IDA raises the issue of a shared underlying mechanism with restless legs syndrome, a sensorimotor dysfunction where iron deficiency increases the severity of the symptoms and iron supplementation ameliorates them. Due to previous findings of decreased motor activity in the laboratory at 12 months during the waking time surrounding an afternoon nap, we also compared those data to a nap in the home. Infants with IDA were less active in the laboratory than in the home. The home versus laboratory results suggest that contextual factors affect the motor activity of IDA infants to a larger extent than controls.

Spontaneous motor activity in human infants with iron-deficiency anemia.

This study compared spontaneous motor activity in 6-month-old Chilean infants with or without iron-deficiency anemia (IDA) who were otherwise healthy. Activity was assessed in conjunction with polysomnographic recording during an afternoon nap in 11 infants with IDA and 15 with normal hemoglobin levels. All infants were given oral iron, and activity was reassessed at 12 and 18 months. Using actigraphs placed on the ankle, the frequency of movement units per minute was determined for each waking/sleep state. The total amount of time infants were in an alert-active state before and after the nap was used to calculate the proportion of movements/minute of waking. There were no differences between anemic and nonanemic infants in total recording time, duration of sleep, or motor activity during sleep. However, infants with IDA showed reduced motor activity during waking at all ages. The magnitude of the differences increased at 12 and 18 months. Thus, IDA was associated with reduced motor activity in infants even after iron treatment. It will be important to confirm these results in a larger sample and to determine the 24-h pattern of motor activity, since reduced motor activity may limit infants' opportunities to explore and learn from the social and physical environment.

Poorer behavioral and developmental outcome more than 10 years after treatment for iron deficiency in infancy.

OBJECTIVE: To determine the long-term effects of iron deficiency in infancy. DESIGN: Longitudinal follow-up study of children who had been tested and treated for iron deficiency as infants. SETTING: Periurban community near San Jose, Costa Rica. PARTICIPANTS: Of the original 191 participants, 87% were reevaluated at 11 to 14 years old (average age: 12.3 years). The children were free of iron deficiency and growing normally by US standards. Those who had chronic, severe iron deficiency in infancy (n = 48) were compared with those who had good iron status before and/or after iron therapy in infancy (n = 114). OUTCOME MEASURES: Comprehensive set of cognitive, socioemotional, and motor tests and measures of school functioning. RESULTS: Children who had severe, chronic iron deficiency in infancy scored lower on measures of mental and motor functioning. After control for background factors, differences remained statistically significant in arithmetic achievement and written expression, motor functioning, and some specific cognitive processes (spatial memory, selective recall, and tachistoscopic threshold). More of the formerly iron-deficient children had repeated a grade and/or been referred for special services or tutoring. Their parents and teachers rated their behavior as more problematic in several areas, agreeing in increased concerns about anxiety/depression, social problems, and attention problems. CONCLUSIONS: Severe, chronic iron deficiency in infancy identifies children who continue at developmental and behavioral risk >10 years after iron treatment.

Cosleeping in context: sleep practices and problems in young children in Japan and the United States.

OBJECTIVE: To determine the relationship between cosleeping and sleep problems in cultures with very different sleep practices. DESIGN: Interview study. SETTING: Families in urban Japan and the United States identified through pediatric and other professional contacts. PARTICIPANTS: Parents of healthy 6- to 48-month-old children (56 Japanese parents and 61 white US parents). All children had been breast-fed and lived in 2-parent, middleclass households. INTERVENTION: None. MAIN OUTCOME MEASURE: Sleep practices and sleep problems. RESULTS: More Japanese than US children coslept 3 or more times per week (59% vs. 15%, P<.001). All cosleeping Japanese children regularly slept all night with their parents (vs. 11% of US cosleepers, P<.001). Japanese and US children did not differ in part-night cosleeping (7% vs. 13%, P = .37). Most Japanese children had adult company and body contact as they fell asleep, and fathers slept separately in 23% of families. A greater proportion of US children had regular bedtime struggles and night waking. Within the US sample, cosleeping was associated with more bedtime struggles (P<.001), night waking (P<.01), and overall stressful sleep problems (P<.01). In the Japanese sample, cosleeping was associated only with night waking (P<.05); however, the proportion of cosleeping Japanese children with frequent night waking was at the level reported for US children who slept alone (30% vs 23%, P = .47). CONCLUSIONS: Cultural differences seem to influence the relationship between sleep practices and sleep problems. The experience of the Japanese families indicates that cosleeping per se is not associated with increased sleep problems in early childhood.