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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 32, No 4, July/August 2021

208

AFRICA

Long-term blood pressure trajectories and associations

with age and body mass index among urban women in

South Africa

Muchiri E Wandai, Samuel OM Manda, Jens Aagaard-Hansen, Shane A Norris

Abstract

Background:

Blood pressure (BP) is known to increase

inevitably with age. Understanding the different ages at which

great gains could be achieved for intervention to prevent and

control BP would be of public health importance.

Methods:

Data collected between 2003 and 2014 from 1 969

women aged 22 to 89 years were used in this study. Growth

curve models were fitted to describe intra- and inter-individ-

ual trajectories. For BP tracking, the intra-class correlation

coefficient (ICC) was used to measure dependency of obser-

vations from the same individual.

Results:

Four patterns were identified: a slow decrease in

BP with age before 30 years; a period of gradual increase

in midlife up to 60 years; a flattening and slightly declining

trend; and another increase in BP in advanced age. These

phases persisted but at slightly lower levels after adjustment

for body mass index. Three groups of increasing trajectories

were identified. The respective number (%) in the low, medium

and highly elevated BP groups were 1 386 (70.4%), 482 (24.5%)

and 101 (5.1%) for systolic BP; and 1 167 (59.3%), 709 (36.0%)

and 93 (4.7%) for diastolic BP. The ICC was strong at 0.71 and

0.79 for systolic and diastolic BP, respectively.

Conclusion:

These results show that BP preventative and

control measures early in life would be beneficial for control

later in life, and since increase in body mass index may worsen

hypertension, it should be prevented early and independently.

Keywords:

blood pressure, hypertension, body mass index, trajec-

tory, intra-class correlation coefficient

Submitted 24/8/20, accepted 31/3/21

Published online 26/7/21

Cardiovasc J Afr

2021;

32

: 208–214

www.cvja.co.za

DOI: 10.5830/CVJA-2021-014

Hypertension is a major risk factor for non-communicable

diseases (NCDs), especially stroke and heart attack,

1

and in South

Africa, it was estimated to account for 19.0% of cardiovascular

disease deaths in 2016.

2

The prevalence of hypertension in

women aged 15 years and older was also estimated at 28.5%,

3

and

increased steeply with age, with 84.0% of women aged 65 years

and older having hypertension.

4

Urban populations have been

shown to have a higher prevalence of hypertension compared

with their rural counterparts,

3

and women in such dwellings have

also been reported to have higher percentages than men.

5,6

Accelerated global efforts for the prevention and control of

NCDs began during the high-level meeting of heads of state and

governments at the 66th session of the United Nations General

Assembly in September 2011.

7

Following this, the South African

Department of Health developed a strategy in line with the

declaration in 2013, of which one of the 10 goals and targets was

to ‘reduce the prevalence of people with raised blood pressure by

20.0% by 2020 (through lifestyle and medication)’.

8

Changes in both systolic (SBP) and diastolic blood pressure

(DBP) with age are known to show an increasing trajectory

that mostly starts between 30 and 40 years.

9-11

However, from

approximately 50 years, DBP may plateau and thereafter start

to decline.

10,11

An individual’s BP trajectory can be used as an

indicator for age-related vascular stiffening or for the existence

of an underlying disease.

12

Growth curves (trajectories) play an important role in life-

course epidemiology,

13

and can be used in identifying groups

of individuals at risk of developing high BP using known risk

factors.

14

In addition, population subgroups with different BP

trajectories can be useful in selecting people who might benefit

most from intervention for the prevention of cardiovascular

disease (CVD) risk.

15

Although age is highly correlated with an increasing BP

trajectory, some studies have however reported a decrease in

SBP and DBP at the population level, especially for communities

in the developed countries of western Europe, Australasia and

North America,

16-18

and this decrease is usually attributed to

lifestyle and pharmacological interventions.

18

Understanding how individuals’ BPs change and how fast

these changes occur (intra-individual change) through their

life course, and the patterns for people with different attributes

(inter-individual differences in the intra-individual change) could

be important in determining best methods for prevention at the

MRC Developmental Pathways for Health Research Unit

(DPHRU), Department of Paediatrics, School of Clinical

Medicine, Faculty of Health Sciences, University of the

Witwatersrand, Johannesburg, South Africa

Muchiri E Wandai, MSc,

muchiriwandai@gmail.com

Shane A Norris, PhD

Biostatistics Research Unit, South African Medical

Research Council (SAMRC); Department of Statistics,

University of Pretoria, Pretoria, South Africa

Samuel OM Manda, PhD

MRC Developmental Pathways for Health Research Unit

(DPHRU), Department of Paediatrics, School of Clinical

Medicine, Faculty of Health Sciences, University of the

Witwatersrand, Johannesburg, South Africa; Health Promotion,

Steno Diabetes Center Copenhagen, Gentofte, Denmark

Jens Aagaard-Hansen, MD, MPH