CARDIOVASCULAR JOURNAL OF AFRICA • Vol 21, No 1, January/February 2010
AFRICA
17
Cardiovascular Topics
The effect of ambient temperature on blood pressure in
a rural West African adult population: a cross-sectional
study
SETOR K KUNUTSOR, JOHN W POWLES
Summary
Introduction:
Associations between ambient temperature
and blood pressure have been demonstrated in countries
where the temperature varies between the seasons. This
phenomenon has been overlooked in blood pressure surveys
in sub-Saharan Africa. We assessed the effect of ambient
temperature on blood pressure in an adult population in a
West African country.
Methods:
A cross-sectional survey was carried out on a rural
Ghanaian population, investigating the effect of ambient
temperature on blood pressure in 574 randomly sampled
adults aged between 18 and 65 years.
Results:
There was a significant inverse relationship between
ambient temperature and systolic (SBP) (
p
<
0.019) and
diastolic blood pressure (DBP) (
p
<
0.036). SBP fell by 5
mmHg per 10ºC rise in ambient temperature.
Conclusion:
Higher ambient temperatures are associated
with lower blood pressures. To enhance comparability of data
from epidemiological surveys, ambient temperature should
be recorded for each blood pressure reading and findings
standardised to a fixed ambient temperature.
Keywords:
blood pressure, ambient temperature, rural, seasons
Submitted 22/5/09, accepted 9/6/09
Cardiovasc J Afr
2010;
21
: 17–20
Seasonal variations in blood pressure have been observed among
adults, children and the elderly in different countries, suggest-
ing that blood pressure is influenced by temperature changes.
Blood pressures have been found to be higher in winter and
lower in summer.
1-4
Woodhouse
et al
.
5
in their study of an elderly
population to determine the seasonal variation in blood pressure
and its relationship to ambient temperature reported that both
systolic (SBP) and diastolic blood pressures (DBP) were highest
during the winter across the whole distribution of blood pressure
readings. Hopman and Remen
6
demonstrated in 1921 that BP
was higher in the colder than the warmer months. Kauffmann
7
showed in 1924 that SBP was 20 to 30 mmHg higher on cool
days than at other times. Brown
8
demonstrated the lowering of
BP in men during the summer period, which was also demon-
strated by Rose.
9
A study conducted among children in Australia
showed that a change of 10ºC in temperature caused an estimated
difference in BP of 5 to 7 mmHg.
10
Despite the extent of evidence on the ambient temperature–
blood pressure phenomenon, not much attention has been paid
to its implications for clinical practice, and quantitative formula-
tions have not been developed to correct for this bias. There are
currently no data published on the relationship between ambient
temperature and blood pressure in sub-Saharan West African
countries, where the seasons are classified into two – the rainy
and dry seasons. Daily maximum temperatures during the dry
season range between 38 and 45ºC and those for the rainy season
are between 20 and 26ºC.
The aim of this study, part of a cross-sectional blood pressure
survey, was to study the influence of ambient temperature on
blood pressure in a rural West African adult population.
Methods
The study was conducted in the Kassena–Nankana District
(KND) of northern Ghana. Ghana is a tropical country located
on West Africa’s Gulf of Guinea, a few degrees north of the
Equator, with a total area of 238 540 km
2
. It has an estimated
population of 19.7 million, a gross domestic product (GDP) of
7.4 billion US dollars and a per capita GDP of 412 US dollars.
KND is one of the eight districts in the northernmost part of
Ghana and Navrongo is its commercial and political capital. It is
a relatively flat country with an area of 1 675 km
2
, which is whol-
ly in the sub-sahelian woodland of West Africa. The vegetation is
guinea savannah, which is characterised by short scattered trees
and a more or less continuous carpet of grasses. The mildly cool
rainy season extends from April to September and the prolonged
and intensely hot, dry season is from October to March. Rainfall
averages from 850 to 950 mm per year, with the peak occurring
in August. Daily mean temperatures range between an average
minimum of 20ºC in the rainy season and an average maximum
of 40ºC in the dry season. In the dry season, early mornings are
usually cool and the afternoons commonly hot with daily maxi-
mum temperatures going as high as 45ºC.
This was part of a cross-sectional survey to determine the
blood pressure levels in a rural West African population. A
random sample of 600 participants was drawn from a popula-
tion register, regularly updated by the Navrongo Demographic
Malaria Consortium, Comdis Muk, Kampala, Uganda
SETOR K KUNUTSOR, MD MSt,
Institute of Public Health, University of Cambridge,
Robinson Way, Cambridge, UK
JOHN W POWLES, MB BS, MA, FPHM
