Q J Med 2000; 93: 557-558
© 2000 Association of Physicians
Correspondence |
Systolic and diastolic blood pressures and urinary sodium excretion in mainland China
Division of Cardiology, Department of Medicine, George Washington University, Washington, DC
Sir,
The relationship of sodium intake to blood pressure and prevalence of hypertension has remained somewhat controversial for many years, despite a large body of evidence from experimental and epidemiological studies across populations supporting a positive correlation between sodium and blood pressure. The report by Cheung et al.1 of a positive correlation between diastolic blood pressure and urinary sodium excretion in 70 hypertensive Hong Kong Chinese patients tends support to the findings of an earlier and much larger nationwide survey of blood pressure, hypertension and sodium intake in 950 356 men and women carried out in mainland China in 1991.2
A positive within-population relationship between sodium intake and blood pressure has been demonstrated in several studies in mainland China, using values of either dietary or urinary sodium.2–5 For instance, in a study of 663 men and women in Tianjin,6 after adjusting for confounding variables, both dietary and urinary sodium and sodium/potassium ratio were significantly and positively correlated with blood pressure. Another population study of the relation between sodium intake and blood pressure conducted in 705 men and women aged 40–59 from two population samples of farmers (one from Shanxi in northern China and the other from Guangxi in southern China) and one of fisherman from Zhejiang of eastern China showed a significant positive association of sodium intake with both systolic and diastolic blood pressures.7
In general, blood pressure and urinary sodium excretion tended to be higher in northern China, e.g. Beijing and Shijiazhuang, than in southern China, e.g. Guangzhou (Figure 1
).8. Of particular interest was the observation that in Guangzhou, a 1989 study showed a gradual rise of both systolic and diastolic blood pressures as compared with a 1985 study, associated with a corresponding increase in urinary sodium excretion. The increase in sodium intake between these two surveys coincided with the rise in the number of American fast-food restaurants, such as MacDonald's and Kentucky Fried Chicken, that had opened in Guangzhou during that period.9
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Hypertension is a very important risk factor for coronary artery disease and stroke in the Chinese population.2,10,11 Stroke is the leading cause of death from cardiovascular diseases in China.2 The 10 Chinese cohorts study showed that each 10 mmHg difference in baseline systolic blood pressure was associated with a 28% difference in risk of coronary artery disease (myocardial infarction, sudden cardiac death and death from congestive heart failure), and each 5 mmHg difference in baseline diastolic blood pressure was associated with a 24% difference in risk of coronary artery disease.2 In Western populations, a reduction in dietary intake of sodium of 100 mmol/24 h (3 g of salt, a realistic reduction) lowers systolic blood pressure in subjects aged 50–65 years by 10 mmHg on average; this reduction in blood pressure would reduce age-specific stroke mortality by 22% and mortality from heart disease by 16%.12 Ecological analysis of the association of population mean blood pressure level with incidence of coronary artery disease and stroke in 14 Chinese populations showed that a 5 mmHg lowering in the population mean level of diastolic blood pressure was associated with 16/100 000 lower incidence of coronary artery disease and 47/100 000 lower incidence of stroke.2
All of the above data confirm that elevation of blood pressure is a very important modifiable risk factor for cardiovascular diseases in China. Cutting salt intake is an important, but relatively simple and inexpensive, step in the control of hypertension in modern China.
References
1.
Cheung BMY, Ho SPC, Cheung AHK, Lau CP. Diastolic blood pressure is related to urinary sodium excretion in hypertensive Chinese patients. Q J Med2000; 93:163–8.
2. Tao SC, Zhou BF. Epidemiology of hypertension in China. Chin Med J1999; 112:878–82.[Medline]
3. Cheng TO. Changing prevalence of heart diseases in People's Republic of China. Ann Intern Med1974; 80:108–9.
4. Cheng TO. Prevalence of cardiovascular diseases among the national minorities of China. Ann Intern Med1984; 101:562–3.
5. Cheng TO. Salt and blood pressure. Lancet1989; 2:214–15.
6. Tian HG, Nan Y, Shao RC, Dong QN, Hu G, Pietinen P, Nissinen A. Associations between blood pressure and dietary intake and urinary excretion of electrolytes in a Chinese population. J Hypertension1995; 13:49–56.[ISI][Medline]
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Zhou BF, Zhang XH, Zhu AM, Zhao LC, Zhu SM, Ruan LS, Zhu LG, Liang SY. The relationship of dietary animal protein and electrolytes to blood pressure: a study on three Chinese populations. Int J Epidemiol1994; 23:716–22.
8. Zhou BF, Wu XG, Tao SQ, Yang, J, Cao TX, Zheng RP, Tian XZ Lu CQ, Miao HY, Ye FM, et al. Dietary patterns in 10 groups and the relationship with blood pressure. Collaborative Study Group for Cardiovascular Diseases and Their Risk Factors. Chin Med J1989; 102:257–61.[Medline]
9. Cheng TO. Cardiovascular disease in China. Nature Medicine1998; 4:1209–10.[ISI][Medline]
10. Cheng TO. Paul D. White Lecture—Cardiology in People's Republic of China. In: Russek HI (ed). New Horizons in Cardiovascular Practice. Baltimore, University Park Press, 1975:1–27.
11. Tung CL, Cheng TO. The changing incidence of heart disease in modern China. In: Cheng TO, ed. The International Textbook of Cardiology. New York, Pergamon Press, 1987:10–14.
12. Law M. Salt, blood pressure and cardiovascular diseases. J Cardiovasc Risk2000; 7:5–8.[ISI][Medline]
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