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(1)

Findings of the International

Cooperative

INTERSALT Study

Stamler J, et al 1991

Hypertpnslon (1 suppl )

(2)

Introduction

• INTERSALT is an international, cooperative, cross-sectional, epidemiological study

• Focusing on the relation of sodium and potassium intake to blood pressure.

• It was deliberately designed to explore these relations

– both within populations, that is, with individuals as the units of measurement and analysis,

– and across populations in whole-population samples

(3)

Methods

• A standardized study

• 10,000 men and women in 52 populations

from 32 countries Africa, North and South

America, Asia, and Europe (north, south,

east, and west)

• Recruit 200 men and women aged 20-59

years , with 25 in each of eight age-sex

groups

(4)

Methods

• Blood pressure (sitting)

– Measured twice with a Hawksley Random Zero sphyg momanometer

– Individual participants was the mean of the two readin gs

• Both "spot" and 24-hour urine.

– Beginning and end of each 24-hour collection were su pervised by clinic staff.

– Urine aliquots were stored locally at -20°C

– Shipped frozen to the Central Laboratory at St. Rapha

(5)

Methods

• Height and weight were each measured twice wi th a stadiometer

• Sodium and potassium excretion

– Measured by emission flame photometry

– The products of concentrations in the urine and urinar y volume corrected to 24 hours

• Alcoholic drinks over the preceding 7 days was a ssessed by questionnaire and converted into vol ume

(6)

Methods

• Data forms were sent to the London Coor

dinating Center for review, editing, coding,

data entry, and analysis.

• Repeat urine collections and blood pressu

re measurements were obtained in a rand

om 8% of participants to estimate intra-indi

vidual variability

(7)

Results and Discussion

Within-Population Findings

• On relations of 24-hour urinary sodium (or

potassium) excretion to blood pressure,

multiple linear regression was used

– One controlled for only age and sex – The other for age, sex, BMI, alcohol

consumption, and 24-hour urinary potassium excretion.

(8)

Results and Discussion

Within-Population Findings --

urinary

sodium

• If no relation between sodium and blood pressure,

– About 26 of these coefficients should have had a positive sign and about 26 a negative sign

• The sodium-systolic blood pressure analysis

– With adjustment for five confounders, there were 33 positive coefficients, with significantly positive

coefficients numbering eight

(9)

Results and Discussion

Within-Popidation Findings --

urinary sodiu m

• Pooling of the 52 within-center regression coefficients, w eighted by the inverse of their variance

– Adjustment for only age and sex, is 3.54 mm Hg SBP/100 mmol 24-hour sodium excretion (Z score, 6.97)

– Adjustment for five confounders, its value is 2.17 (Z score, 3.79)

• with the exclusion of four centers from remote population s exhibiting low and very low median sodium intake

– Their Z scores was 6.93 when adjusted for only age and sex – Adjustment for five confounders, Z score was 3.69).

(10)
(11)

Results and Discussion

Within-Population Findings —

Na/K ratio

• The sign of the coefficient was positive for 37 of t he 52 multivariate analyses, with p 0.05 for eig ht of these; no coefficient was significantly negati ve

• Adjustment for only age and sex, is 2.10 mm Hg SBP/ Na/K ratio, adjustment for five confounders , its value is 1.61

• Both coefficients were significant for the sodium/ potassium ratio and diastolic blood pressure but smaller than for the sodium/potassium ratio and systolic blood pressure

(12)
(13)

Results and Discussion

Within-Population Findings --

urinary potassium

• With five-factor adjustment, significant

inverse relations were recorded for 24-

hour urinary potassium excretion and both

systolic and diastolic blood pressures

(14)
(15)

Results and Discussion

Within-Population Findings

• Both BMI and heavy alcohol consumption

were significantly and independently relate

d to systolic and diastolic blood pressures

(p<0.001)

(16)

Results and Discussion

Within-Popidation Findings

The relations between 24-hour urinary

electrolyte excretion and blood pressure,

(Table 2)

• For men aged 40-59 years,

– Significant for the regressions of SBP on both sodium and the sodium/potassium ratio

– Inverse significant for the regression of SBP on potassium

• The findings are similar for women

(17)
(18)

Urinary Sodium Excretion VS.

Blood Pressure

For several reasons, these coefficients reflecting the relati ons of 24-hour urinary sodium excretion to blood pressur e of individuals sizably underestimate the true effects. 1) The study was cross-sectional, relating current sodium e

xcretion to current blood pressure. Exposure since childh ood, even from birth, is probably important.

2) One measurement of 24-hour sodium excretion is a wea k method of quantifying habitual sodium intake of an indi vidual because of large withinindividual variability. This er ror tended to bias the true sodium-blood pressure relatio ns toward zero.

(19)

3) it is probable that there were varying degrees of incompleteness of 24-hour urine collection in

some or all centers. This shortcoming also

tended to produce underestimates of the true associations.

4) Public health and medical care campaigns in several countries (e.g., the United States and Japan) have recommended a reduction in salt intake. it would tend to bias sodium-blood

pressure associations downward or even convert positive relations to negative ones.

(20)

5) Some persons in most centers were on

antihypertensive drugs (a majority at older ages in some centers). Their blood pressures were artificially low, tending to reduce sodium-blood pressure relations.

6) Adjustment for body mass index and other confounders, which are more accurately

measured than sodium excretion and positively correlated with it, may have underestimated the

(21)

Results and Discussion

Cross-Population Findings

• 24-hour sodium excretion ranged from 0.2 mmol /24 hr ( Yanomamo, Brazil) to 242.1 mmol/24 hr (Tianjin, China)

• But none came close to the level reported for the northern Japanese in Dahl's famous figure—abo ut 435 mmol sodium/24 hr.

• 36 of the 52 centers (69%) had median 24-hour sodium excretions clustered in the range of 130- 179 mmol/24 hr

(22)

Results and Discussion

Cross-Population Findings

• With adjustment for age, sex, BMI, and alcohol consump tion (Figures 1 and 2)

• Slope for SBP or DBP with age on sample median 24-ho ur sodium excretion for 52 samples was significant (p<0. 001) ; for remain 48 samples, it was also significant (p< 0.01)

• The value for the slope of SBP with age is 0.34 mm Hg/1 00 mmol sodium/yr.

• That is, for a person who habitually eats 70 mmol sodiu m/day compared with one who eats 170 mmol sodium/d ay, a slope upward in systolic blood pressure from age 2 5 to age 55 is estimated to be less by 10.2 mm Hg.

(23)
(24)
(25)

Results and Discussion

--- four low sodium centers

• Four centers with low median sodium intak

e (Yanomamo and Xingu Indians of Brazil,

Papua New Guinea highlanders, and rural

Kenyans)

(Table 3)

– Their median SBP and DBP values were low – The slope of systolic and diastolic blood press

ures with age varied little or not at all from zer o

– The prevalence of high blood pressure was v ery low

(26)
(27)

Conclusion

• The significant, positive, independent findings of INTERSALT on sodium and blood pressure are concordant with a vast array of data from all major research disciplines.

• The INTERSALT data lend further substantive support to the judgment that the habitually high salt intake common in most populations (at levels several times above

physiological need) is among the key etiological factors producing the rise in blood pressure found in a majority of people in these populations over the decades from youth through middle age.

• This elevated salt intake is one of the key mass

exposures accounting for the high prevalence rates of frank hypertension in most contemporary societies.

参照

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