Seungmi Yang

Variation in Child Cognitive Ability by Week of Gestation Among Healthy Term Births

The authors investigated variations in cognitive ability by gestational age among 13,824 children at age 6.5 years who were born at term with normal weight, using data from a prospective cohort recruited in 1996-1997 in Belarus. The mean differences in the Wechsler Abbreviated Scales of Intelligence were examined by gestational age in completed weeks and by fetal growth after controlling for maternal and family characteristics. Compared with the score for those born at 39-41 weeks, the full-scale intelligence quotient (IQ) score was 1.7 points (95% confidence interval (CI): -2.7, -0.7) lower in children born at 37 weeks and 0.4 points (95% CI: -1.1, 0.02) lower at 38 weeks after controlling for confounders. There was also a graded relation in postterm children: a 0.5-points (95% CI: -2.6, 1.6) lower score at 42 weeks and 6.0 points (95% CI: -15.1, 3.1) lower at 43 weeks. Compared with children born large for gestational age (>90th percentile), children born small for gestational age (<10th percentile) had the lowest IQ, followed by those at the 10th-50th percentile and those at the >50th-90th percentile. These findings suggest that, even among healthy children born at term, cognitive ability at age 6.5 years is lower in those born at 37 or 38 weeks and those with suboptimal fetal growth.

The contribution of material, psychosocial, and behavioral factors in explaining educational and occupational mortality inequalities in a nationally representative sample of South Koreans: Relative and absolute perspectives

The contributions of material, psychosocial, and behavioral factors in explaining socioeconomic inequalities in health have been explored in many Western studies. Most prior investigations have looked at relative abilities to explain such inequalities. In addition, little research focuses on Asian countries, despite the fact that the prevalence and socioeconomic distribution of risk factors for mortality are different there. This study examined relative and absolute abilities of material, psychosocial, and behavioral pathways to explain educational and occupational inequalities in mortality in a nationally representative sample from South Korea. The 1998 and 2001 National Health and Nutrition Examination Survey data were pooled and linked to national mortality data. Of 8366 men and women over 30 years of age, 310 died between 1999 and 2005. Nine pathway variables were examined: three material factors (income, health insurance, and car ownership status), three psychosocial factors (depression, stress, and marital status), and three behavioral factors (smoking, alcohol consumption, and physical exercise). The relative risk and relative index of inequality were used as measures of relative inequality, and risk differences and the slope index of inequality were used as measures of absolute inequality. Material factors explained a total of 29.0% of the excess in relative risk for education and 50.0% of the excess in relative risk for occupational class. Material factors explained 78.6% of the excess in absolute mortality difference for education and 41.1% for occupational class. Psychosocial factors for both education and occupational class had a relative and absolute explanatory power of less than 15%. Behavioral factors showed a relative explanatory power of about 15%, but absolute explanatory power reached 84.0% for education and 105.4% for occupational class. However, the number of deaths used to calculate the absolute explanatory power was small. Results of this study suggest that absolute socioeconomic mortality inequalities could be substantially reduced if behavioral risk factors were reduced in the whole population.

Understanding the rapid increase in life expectancy in South Korea

OBJECTIVES We assessed life expectancy increases in the past several decades in South Korea by age and specific causes of death. METHODS We applied Arriagas decomposition method to life table data (1970-2005) and mortality statistics (1983-2005) to estimate age- and cause-specific contributions to changes in life expectancy. RESULTS Reductions in infant mortality made the largest age-group contribution to the life expectancy increase. Reductions in cardiovascular diseases (particularly stroke and hypertensive diseases) contributed most to longer life expectancy between 1983 and 2005 (30% in males and 28% in females). Lower rates of stomach cancer, liver disease, tuberculosis, and external-cause mortality accounted for 30% of the male and 20% of the female increase in longevity. However, higher mortality from ischemic heart disease, lung and bronchial cancer, colorectal cancer, breast cancer, diabetes, and suicide offset gains by 10% in both genders. CONCLUSIONS Rapid increases in life expectancy in South Korea were mostly achieved by reductions in infant mortality and in diseases related to infections and blood pressure.

Emergence of Socioeconomic Inequalities in Smoking and Overweight and Obesity in Early Adulthood: The National Longitudinal Study of Adolescent Health

OBJECTIVES We examined whether socioeconomic inequalities in smoking and overweight and obesity emerged in early adulthood and the contribution of family background, adolescent smoking, and body mass index to socioeconomic inequalities. METHODS Using data from the National Longitudinal Study of Adolescent Health we employed multinomial regression analyses to estimate relative odds of heavy or light-to-moderate smoking to nonsmoking and of overweight or obesity to normal weight. RESULTS For smoking, we found inequalities by young adult socioeconomic position in both genders after controlling for family background and smoking during adolescence. However, family socioeconomic position was not strongly associated with smoking in early adulthood. For overweight and obesity, we found socioeconomic inequalities only among women both by young adult and family socioeconomic position after adjusting for birthweight, other family background, and body mass index during adolescence. CONCLUSIONS Socioeconomic inequalities in smoking emerged in early adulthood according to socioeconomic position. Among women, inequalities in overweight or obesity were already evident by family socioeconomic position and strengthened by their own socioeconomic position. The relative importance of family background and current socioeconomic circumstances varied between smoking and overweight or obesity.

Exposure to parental smoking and child growth and development: a cohort study

BackgroundStudies on adverse childhood health and development outcomes associated with parental smoking have shown inconsistent results. Using a cohort of Belarusian children, we examined differences in cognition, behaviors, growth, adiposity, and blood pressure at 6.5 years according to prenatal and postnatal exposure to parental smoking.MethodsUsing cluster-adjusted multivariable regression, effects of exposure to prenatal smoking were examined by comparing (1) children whose mothers smoked during pregnancy with those of mothers who smoked neither during nor after pregnancy and (2) children whose mothers smoked during and after pregnancy with those whose mothers smoked after pregnancy only; effects of postnatal smoking were examined by comparing (1) children whose mothers smoked after pregnancy only with those of mothers who smoked neither during nor after pregnancy and (2) children whose fathers smoked with those whose fathers did not smoke among children of non-smoking mothers after adjusting for a wide range of socioeconomic and family characteristics.ResultsAfter adjusting for confounders, children exposed vs unexposed to prenatal maternal smoking had no differences in mean IQ, teacher-rated behavioral problems, adiposity, or blood pressure. Children exposed to maternal postnatal smoking had slightly increased behavioral problems [0.9, 95% CI: 0.6, 1.2 for total difficulties], higher body mass index [0.2, 95% CI: 0.1, 0.3], greater total skinfold thickness [0.4, 95% CI: 0.04, 0.71], and higher odds of overweight or obesity [1.4, 95% CI; 1.1, 1.7]. Similar magnitudes of association were observed with postnatal paternal smoking.ConclusionsNo adverse cognitive, behavioral and developmental outcomes were associated with exposure to maternal prenatal smoking. Observed associations with postnatal smoking of both parents may reflect residual confounding by genetic and family environmental factors.

Decomposition of socio-economic differences in life expectancy at birth by age and cause of death among 4 million South Korean public servants and their dependents

BACKGROUND Differences in life expectancy at birth across social classes can be more easily interpreted as a measure of absolute inequalities in survival. This study quantified age- and cause-specific contributions to life expectancy differences by income among 4 million public servants and their dependents in South Korea (9.1% of the total Korean population). METHODS Using 9-year mortality follow-up data (208,612 deaths) on 4,055,150 men and women aged 0-94 years, with national health insurance premiums imposed proportionally based on monthly salary as a measure of income, differences in life expectancy at birth by income were estimated by age- and cause-specific mortality differences using Arriagas decomposition method. RESULTS Life expectancy at birth gradually increased with income. Differences in life expectancy at birth between the highest and the lowest income quartile were 6.22 years in men and 1.74 years in women. Mortality differentials by income among those aged ≥50 years contributed most substantially (80.4% in men and 85.6% in women) to the socio-economic differences in life expectancy at birth. In men, cancers (stomach, liver and lung), cardiovascular diseases (stroke), digestive diseases (liver cirrhosis) and external causes (transport accidents and suicide) were important contributors to the life expectancy differences. In women, the contribution of ill-defined causes was most important. Cardiovascular diseases (stroke and hypertensive disease) and external causes (transport accidents and suicide) also contributed to the life expectancy differences in women while the contributions of cancers and digestive diseases were minimal. CONCLUSIONS Reductions in socio-economic differentials in mortality from stroke and external causes (transport accidents and suicide) among middle-aged and older men and women would significantly contribute to equalizing life expectancy among income groups. Policy efforts to reduce mortality differentials in major cancers (stomach, liver and lung) and liver cirrhosis are also important for eliminating Korean mens socio-economic inequalities in life expectancy.

Birth Weight and Cognitive Ability in Childhood Among Siblings and Nonsiblings

OBJECTIVES. The purpose of this work was to examine whether the positive association between birth weight and childhood cognitive ability is seen within siblings from the same family, as well as between nonsiblings, and to determine whether these associations vary with age. METHODS. We compared the association of birth weight with cognitive ability measured at ages 5 to 6, 7 to 9, and 11 to 12 years among a total of 5402 children from different families with that among 2236 to 3083 sibships from the National Longitudinal Study of Youth 1979-Children. RESULTS. In the whole cohort, there were positive associations between birth weight and cognitive ability at all ages, with the association increasing with age from a 0.81-point increase at ages 5 to 6 years to 1.30 and 1.44 points at ages 7 to 9 and 11 to 12 years, respectively, per 1 SD of gestational age- and gender-adjusted birth weight z score. With adjustment for covariates, there was marked attenuation of these associations. Mean differences were 0.28 points in children aged 5 to 6 years, 0.67 points in those aged 7 to 9 years, and 0.52 points in those aged 11 to 12 years after adjusting for childs gender, race or ethnicity, year of birth, and age at test; maternal age, height, parity, education, smoking during pregnancy, and cognitive ability; and household income. Our family-based analyses that separated within- and between-family effects found that the between-family associations were much stronger than the within-family associations. However, adjustment for potential confounders attenuated the between-family associations, and there was no evidence for a difference in association comparing the between- and within-family associations. CONCLUSIONS. In these data, the positive association between birth weight and childhood cognitive ability at ages 5 to 12 years is explained largely by family characteristics rather than a specific intrauterine effect.

Do population-based interventions widen or narrow socioeconomic inequalities? The case of breastfeeding promotion

BACKGROUND Despite numerous population-based randomized intervention trials, the impact of such interventions on socioeconomic inequalities has rarely been examined. We used data from a large cluster-randomized trial to assess the impact of a breastfeeding promotion intervention on socioeconomic inequalities in breastfeeding (exclusivity and duration) and in child cognitive ability at early school age. METHODS The Promotion of Breastfeeding Intervention Trial (PROBIT) randomized 31 Belarusian maternity hospitals and their affiliated polyclinics either to receive a breastfeeding promotion intervention modelled on the WHO/UNICEF Baby-Friendly Hospital Initiative or to continue the standard practices in effect at the time of randomization. We estimated and compared inequalities in discontinuation of exclusive breastfeeding before 3 months and of any breastfeeding before 12 months and in child verbal IQ at age 6.5 years, across maternal education strata between the two intervention arms. FINDINGS Socioeconomic inequalities in discontinuing exclusive breastfeeding before 3 months were negligible in the control group. However, graded inequalities by maternal education emerged in the intervention group {relative risk [RR] = 1.12 [95% confidence interval (CI): 1.04, 1.20] for partial university and RR = 1.20 [95% CI: 1.11, 1.31] for secondary education or less vs complete university; risk difference [RD] = 0.06 [95% CI: 0.03, 0.09] and 0.10 [95% CI: 0.06, 0.14], respectively}. For discontinuing any breastfeeding before 12 months, small socioeconomic gradients in the control group were widened in the intervention group (RR = 1.04 and 1.16, respectively, for mothers with secondary education or less). Despite these differential effects on breastfeeding, however, we observed a small, nonsignificant reduction in socioeconomic inequalities in child verbal IQ at age 6.5 years. CONCLUSIONS A population-based intervention to promote breastfeeding slightly widened socioeconomic inequalities in breastfeeding but not those in child cognitive ability.

Duration of gestation, size at birth and later childhood behaviour

Although many previous studies have reported an association between preterm birth or small size at birth and later behaviour, multiple methodological limitations threaten the validity of causal inferences from reported associations. The authors have examined the association between gestational age and gestational age-specific size at birth (weight, length and head circumference) and behaviour in a large sample of children born healthy at term. The data were from the 6.5-year follow-up of 13,889 Belarusian children who participated in the Promotion of Breastfeeding Intervention Trial, a cluster-randomised trial of a breast-feeding promotion intervention. Child behaviour was measured using the parent and teacher versions of the Strengths and Difficulties Questionnaire (SDQ). Differences in SDQ scores by gestational age and by birthweight, birth length and birth head circumference standardised for gestational age and sex (z-scores) were analysed after controlling for potentially confounding maternal and family factors. There was no association between gestational age and child behaviour after adjusting for potential confounding factors. Lower birthweight-for-gestational age was associated with higher scores in problem behaviours including total difficulties, conduct problems, hyperactivity, emotional symptoms and peer problems. Similar but smaller differences were observed with birth length and birth head circumference, but those differences were attenuated with adjustment for birthweight. The patterns of association were consistent in both parent and teacher assessments. Among school-age children born at term within normal range of birthweight, fetal growth, but not gestational age, was associated with behavioural problem scores.

The changing gender differences in life expectancy in Korea 1970-2005

Women live much longer than men in Korea, with remarkable gains in life expectancy at birth for the past decades. The gender differential has steadily increased over time, reaching a peak of more than 8 years in 1980s, and decreased thereafter to 6.7 years in 2005. Studies to investigate the pattern and contributing factors to changes in the life expectancy gender gap have been mostly from Western countries, and there has been no such study in Asian countries, except in Japan. We therefore aimed to examine age- and cause-specific contributions to the changing gender differentials in life expectancy in Korea, in particular the decline of the gap, using a decomposition method. Between 1970 and 1979 when the gender gap in life expectancy widened, faster mortality decline among women in ages 20-44 explained 66% of the total increase in the gender gap, which would be due to substantial improvements in reproductive health among women and excess male mortality in occupational injuries and transport accidents. Although greater survival advantage among elderly women over 70 contributed to further increase in the gender gap, the contributions from younger ages with the ages 15-64 contributing the most (-2 years) resulted in the overall reduction of the gender gap which began in 1992 and continued to 2005. Among causes of death, liver diseases (-0.5 years, 38% of the total decline), transport accidents (-0.4 years, 31%), hypertensive diseases (-0.3 years, 19%), stroke (-0.1 years, 11%), and tuberculosis (-0.1 years) contributed the most to the overall 1.4 years reduction in the gender gap. However, changes in mortality from lung cancer (+0.3 years), suicide (+0.3 years), chronic lower respiratory diseases (+0.2 years), and ischemic heart diseases (+0.1 years) contributed to widening the gap during the same period. In sum, while smoking-related causes of death have contributed most to the narrowing gap in most other industrialized countries, these causes contributed toward increasing the gender gap in Korea. Instead, liver disease, hypertension-related diseases, and transport accidents were major contributing causes of death to the narrowing of gender differentials in life expectancy in Korea.