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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.zaDOI: 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.comShane 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