Juliana Kagura

Association of socioeconomic status change between infancy and adolescence, and blood pressure, in South African young adults: Birth to Twenty Cohort.

Objective Social epidemiology models suggest that socioeconomic status (SES) mobility across the life course affects blood pressure. The aim of this study was to investigate the association between SES change between infancy and adolescence, and blood pressure, in young adults, and the impact of early growth on this relationship. Setting Data for this study were obtained from a ‘Birth to Twenty’ cohort in Soweto, Johannesburg, in South Africa. Participants The study included 838 Black participants aged 18 years who had household SES measures in infancy and at adolescence, anthropometry at 0, 2, 4 and 18 years of age and blood pressure at the age of 18 years. Methods We computed SES change using asset-based household SES in infancy and during adolescence as an exposure variable, and blood pressure and hypertension status as outcomes. Multivariate linear and logistic regressions were used to investigate the associations between SES change from infancy to adolescence, and age, height and sex-specific blood pressure and hypertension prevalence after adjusting for confounders. Results Compared to a persistent low SES, an upward SES change from low to high SES tertile between infancy and adolescence was significantly associated with lower systolic blood pressure (SBP) at the age of 18 years (β=−4.85; 95% CI −8.22 to −1.48; p<0.01; r2=0.1804) after adjusting for SES in infancy, small-for-gestational-age (SGA) and weight gain. Associations between SES change and SBP were partly explained by weight gain between birth and the age of 18 years. There was no association between SES mobility and diastolic blood pressure, mean arterial pressure or hypertension status. Conclusions Our study confirms that upward SES change has a protective effect on SBP by the time participants reach young adulthood. Socioeconomic policies and interventions that address inequality may have the potential to reduce cardiovascular disease burden related to BP in later life.

Association Between Early Life Growth and Blood Pressure Trajectories in Black South African Children

Early growth is associated with blood pressure measured on one occasion, but whether early life growth patterns are associated with longitudinal blood pressure trajectories is under-researched. Therefore, we sought to examine the association between early growth and blood pressure trajectories from childhood to adulthood. Blood pressure was measured on 7 occasions between ages 5 and 18 years in the Birth to Twenty cohort study, and conditional variables for growth in infancy and mid-childhood were computed from anthropometric measures (n=1937, 52% girls). We used a group-based trajectory modeling approach to identify distinct height-adjusted blood pressure trajectories and then tested their association with growth between birth and mid-childhood adjusting for several covariates. Three trajectory groups were identified for systolic and diastolic blood pressure: lower, middle, and upper in boys and girls, separately. In boys, predictors of the middle or upper systolic blood pressure trajectories versus the lower trajectory were in birth weight (odds ratio 0.75 [95% confidence interval 0.58–0.96] per SD) and relative weight gain in infancy (4.11 [1.25–13.51] per SD). In girls, greater relative weight gain and linear growth in both infancy and mid-childhood were consistently associated with an almost 2-fold higher likelihood of being in the upper versus lower systolic blood pressure trajectory. The associations for the diastolic blood pressure trajectories were inconsistent. These findings emphasize the importance of identifying children at risk of progression to high blood pressure. Accelerated growth in infancy and mid-childhood may be a key target for early life intervention in prevention of elevated blood pressure progression.

Relationship between early growth and CVD risk factors in adolescents.

Low birth weight and a rapid weight gain in early childhood may lead to an increased risk for developing cardiovascular disease later in life, such as hypertension and dyslipidaemia. In this study, we examined the associations between size at birth, relative weight gain in infancy and childhood with specific cardiovascular disease risk factors in early adulthood. Adolescents (n=1935) from the Birth to Twenty plus (BT20+) cohort were included in the analysis. The following were treated as exposure variables: weight at birth, and relative conditional weight gain (CW), independent of height, between ages 0-24 months and 24-48 months. Outcomes were serum lipids and body composition variables at age 18 years. After adjusting for sex and other confounders, early life exposures were not associated with adolescent lipid profile. Following adjustment for sex and height (body size), birth weight [β=0.704 (0.40, 1.01)], CW 0-24 [β=1.918 (1.56, 2.28)] and CW24-48 [β=1.485 (1.14, 1.82)] accounted for 48% of the variance in fat mass. However, birth weight [β=0.773 (0.54, 1.01)], CW 0-24 [β=1.523 (1.24, 1.80)] and CW24-48 [β=1.226 (0.97, 1.49)] were also positively predicted and accounted for 71% of the variance in fat mass in adolescence (P<0.05). Our data suggests that birth weight and weight gain during infancy and early childhood independent of linear growth are related to adolescent body composition but not blood lipid profiles in an urban African population.

Association between infant nutrition and anthropometry, and pre-pubertal body composition in urban South African children.

Early life nutrition and growth are related to subsequent obesity risk in high-income countries. We investigated the association between nutrition and growth during infancy, and body composition at 10 years of age in 140 children selected from the Bone Health sub-study of the Birth-to-Twenty cohort from Soweto, Johannesburg, South Africa. Infant feeding and dietary data were collected during the first 12 months, and weight and height were measured at 1 and 2 years of age. At 10 years, anthropometry and dual-energy X-ray absorptiometry (DXA)-derived body composition were measured. Regression models were used to determine associations between independent and dependent variables at the 1% level of significance. A one z-score increase in birth weight was associated with a 1051 g increase in lean mass and a 0.22 increase in body mass index (BMI) z-score at the age of 10 years. After adjusting for confounders, stunting at age 1 year was associated with lower fat mass only at 10 years of age while at age 2 years, it was associated with lower lean mass only. Being underweight at one year of age was significantly associated with lower lean mass only. Weight-for-age (WAZ) change in the second year of infancy was a predictor of fat mass and BMI only. Body fatness at 10 years of age was positively associated with infant WAZ change rather than height-for-age change. There were no significant associations between infant dietary patterns, wasting and being underweight at age 2 years and pre-pubertal body composition. Further studies are needed to assess whether these associations continue during adolescence as pubertal development may be an important modifier of these associations.

Environmental lead exposure and pubertal trajectory classes in South African adolescent males and females

The effects of environmental lead exposure in the neuro-endocrine system have been shown to impact the maturation and tempo of puberty development in adolescents. In low and middle income countries very little is known regarding the detrimental health effects of childhood lead exposure with regard to the tempo of puberty development. To help address this gap in data, we examined the association between lead exposure and puberty progression in males and females. Study participants from the urban Birth to Twenty Plus (BT20+) birth cohort in Soweto-Johannesburg, South Africa with data for blood lead levels at age 13years, cord blood lead levels, pubic hair development and breast development in females, and pubic hair development and genital development in males, were included in this study. The sample comprised 1416 study participants (n=684 females). Pubertal development trajectory classes were defined using Latent Class Growth Analysis. Data were examined for (i) an association between cord blood lead levels and pubertal trajectory classes; and (ii) an association between blood lead levels at age 13years and pubertal trajectory classes. In females, there was an association between adolescent elevated blood lead levels (≥5μg/dL) and lower level of maturation at age 9years and slower progression of pubic hair and breast development (relative risk ratio (RRR)=0.45, p<0.0001; 95% CI (0.29-0.68)) and (RRR=0.46, p<0.01; 95% CI (0.27-0.77)), respectively. In males, elevated blood lead levels at birth were associated with slower tempo of pubic hair development (RRR=0.20, p<0.05). Findings from this study suggest a possible role for environmental lead in altering pubertal development in South African adolescents as shown by slower tempo of progression through the Tanner stages pubertal development in females and males. There were also gender-differences between the effects of prenatal and postnatal lead exposure during pubertal development.

Demographic, socio-economic and behavioural correlates of BMI in middle-aged black men and women from urban Johannesburg, South Africa

ABSTRACT Background: There is a high and increasing prevalence of overweight and obesity in South Africans of all ages. Risk factors associated with overweight and obesity must be identified to provide targets for intervention. Objective: To identify the demographic, socio-economic and behavioural factors associated with body mass index (BMI) in middle-aged black South African men and women. Methods: Data on demographic and socio-economic factors were collected via questionnaire on 1027 men and 1008 women from Soweto Johannesburg, South Africa. Weight and height were measured and BMI was determined. Behavioural factors included tobacco use and consumption of alcohol, and physical activity data were collected using the Global Physical Activity Questionnaire. Menopausal status was determined for the women, and HIV status was available for 93.6% of the men and 39.9% of the women. Results: Significantly more women were overweight or obese than men (87.9 vs. 44.9%). Smoking prevalence (current or former) and minutes spent in moderate to vigorous intensity physical activity was significantly different between the sexes (both p < 0.0001). In the final hierarchical model, marital status (+ married/cohabiting), household asset score (+), current smoking (-), moderate to vigorous physical activity (-) and HIV status (- HIV infected) significantly contributed to 26% of the variance in BMI in the men. In the women, home language (Tswana-speaking compared to Zulu-speaking), marital status (+ unmarried/cohabiting), education (-), current smoking (-) and HIV status (- HIV infected) significantly contributed to 14% of the variance in BMI. Conclusions: The sex difference in BMI and the prevalence of overweight and obesity between black South African men and women from Soweto, as well as the sex-specific associations with various demographic, socio-economic and behavioural factors, highlight the need for more tailored interventions to slow down the obesity epidemic.