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A correlation between blood pressure and weight was shown in both populations but this
could noi account for the extent of the differences observed.
This focussed attenLion on other possible factors including habitual salt intake and
stress. Measurements of s[ress are difficult to carry out and to quantify and were not
pursued at that time. These studies showed significant differences in the habitual salt use
between Pukapuka and Rarotonga which gave important insights in[o the part sodium and
potassium intake may play in relation to blood pressure level in communities. The intake was
t0rrrnoIlZ4 hours in Pukapuka and 120-140 mmoll?4 hours in Rarotonga (Prior et e!., f968).
Subsequent work by Page and the Harvard group has examined the relationship between
salt user and blood pressure in Solomon Island groups (Page et !, L97q. They showed that
while all groups had low pressures, the levels were cert,ainly hfuher in those from the area
where cooking nrethods and catering customs gave them a notably higher sodium intake.
These natural experiments from the Pacific have strengthened the hypothesis of a link
between hsbitual salt use and blood pressure, and has given zupporl to the hypothesis that
within a community there are some people and familier more sensitive to salt intake than
others who, above a certain threshold, will respond by developing hypertension. Below this
threshold of around 40-60 mmols blood pressures remain lower and hypertension does not
develop.
The data collected by the Epidemiology Unit in Cook Islands, Tonga and Tokelau
support this hypothesis in a general way without being able to show a consistent within
population relationship of blood pressure to salt intake.
It is now recognized that intake of potassium containing foods may have a protective
effect tending to lower blood pressure and a high intake of potassium in many of the low
blood pressure populations zupports this. The correlation of the urinary sodium to potassium
ratio with systolic and diastolic blood pressure shows a definite contribution in some studies,
This effect was not apparent in those seen in Tokelau but becomes a definite contributing
factor to blood ptessure with the increasing time Tokelauans live in New Zealand where they
move mto a higher sodium and lower potassium intake.
There is now reasonable evidenee to show that a high potassium intake is in fact
protective against blood pressure increase and this reinforces the conclusion that any efforts
to restrict sodium input should be linked with high potassium intake through a diet rich in
vegetables and potassium rich substances (McGregor, fggJ).
Other research is seeking to test whether there is a genetic abnormality present in
zubject who have hypertension and in their children before the condition is apparent in Lhe
latter (Garay and Meyer, 1919). The red cell is used as a nndel to represent how the muscle
eell of the wall of the small arterioles or blood vessels rnay be responding to sodium and
potassium. Evidence is suggesting that the rnembrane of the ned cell and white cells do react
in an abnormal way indicating some abnormality in sodium pump mechanism whereby sodium
content in red and white cells is increased in subjects with essential hypertension and also in
their norrnotensive children. This is considered as a genetie abnormality and could help
establish the genetic contribution in s.rbjects developing hypertension. It could also identify
wbjects at higher risk before hypertension had declared itself.
This rcpnesent an exciting developrnent that is very relevant to the perspective we are
considoringr particularly as there is the opportunity to examine such biological factors in
strbjecls undergoing migration and changes in blood pressure.
This example is set out in some detail to illustrate how epidemiology as a discipline can
help in the generation of rientific hypotheses and how the Pacific work had nrade its
contribution to areas that can now be moved forward by detailed basic research at cellulan
and rnembrane level. The next phase represents development of intervention programmes at
the conmunity level in order to test further the part aalt restriction and potassium increase
can play in lowering blood pressures and reducing the attributable community risk of
hypertension and its complicaLions. We will return to this when considering the future of the
Pacific Island regions in the period of the I980s to 2000.