Blood pressure tracking in urban black South African children: Birth to twenty cohort

Background: Hypertension is an emerging public health problem in South Africa. Recent evidence from longitudinal studies has shown that hypertension in adulthood can be traced back to childhood. There is scarcity of longitudinal data on paediatric blood pressure (BP) particularly in African populations. The objective of this study is to assess the prevalence of hypertension and evaluate BP tracking between childhood and late adolescence among South African black Children. Methods: This study utilized data from the Birth to Twenty cohort, which is comprised of children born in Soweto, Johannesburg in 1990 (N=3273, 78.5 % black). Data on BP and anthropometry were collected at six follow-up periods between ages 5 and 18 years. Blood pressure status was classified using the Fourth report on National High Blood pressure program in children and adolescents. Pearson correlation coefficients and relative risk ratios (RR) were used to describe tracking of BP between childhood and late adolescence. Results: The overall point prevalence ranged from 9.2 to 16.4 % for prehypertension and 8.4 to 24.4 % for hypertension. Tracking coefficients ranged from 0.20 to 0.57 for SBP and 0.17-0.51 for DBP in both sexes over the 14 years of measurement. The proportion of children who maintained an elevated BP status between childhood, adolescence and age 18 years ranged from 36.1% at age 5 years to 56.3 % at age 13 years. Risk of having elevated BP at 18 years ranged from; RR: 1.60 (95 % CI: 1.29-2.00) at 5 years to RR: 2.71 (95 % CI: 2.32-3.17) at 14 years of age. Conclusions: This study reports high prevalence of elevated BP which tracks from early childhood into late adolescence. These findings emphasize the importance of early identification of children at risk of developing elevated BP and related risk factors plus timely intervention to prevent hypertension in adulthood.