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Journal of Human Hypertension (2001) 15, 487–493  2001 Nature Publishing Group All rights reserved 0950-9240/01 $15.00 www.nature.com/jhh

ORIGINAL ARTICLE

A comparison of dietary and non-dietary factors of hypertension and normal blood pressure in a Chinese population G Hu1 and H Tian2 1 Department of Physiology, University of Kuopio, Kuopio, Finland; 2Food Safety Control and Inspection Institute Tianjin, Tianjin, The People’s Republic of China

The aim of this study was to compare the differences of dietary and non-dietary factors in hypertension and normal blood pressure (BP) of Chinese urban people. Two cross-sectional population surveys were carried out in Tianjin, one of the three largest cities in China. A total of 2068 subjects aged 35–64 years were selected by a random stratified cluster sampling, 367 men and 395 women were hypertensive, and 623 men and 683 women had normal BP. The diet was assessed by food weighing plus consecutive individual 3-day food records. Health status, health behaviours and anthropomentry were assessed. The whole population had a high

sodium and low potassium consumption level. Hypertensive men and women had significantly higher daily dietary sodium intake (P ⬍ 0.05) and hypertensive women had higher dietary sodium-to-potassium ratio (P ⬍ 0.01) than men and women with normal BP. Age, body mass index, overweight and family history of hypertension were positively related to high BP. Dietary sodium intake and dietary sodium-to-potassium ratio were positively associated with high BP. Education level in women and commuting physical activity in men were inversely associated with high BP. Journal of Human Hypertension (2001) 15, 487–493

Keywords: diet; non-dietary factors; normal blood pressure; Chinese

Introduction Hypertension is a massive problem not only for economically developed countries,1 but also for developing countries, such as China. The prevalence of hypertension increased from 7.7% in 1980 to 11.9% in 1991, when hypertension was defined as systolic blood pressure (SBP) of at least 140 mm Hg, or diastolic blood pressure (DBP) of at least 90 mm Hg.2 Epidemiological studies have shown that the prevalence of hypertension varies widely across the different regions of China, with higher rates in the north than in the south. Beijing, Tianjin and Tibet are the three regions with the highest prevalence of hypertension.2,3 In Tianjin, located in north China and the third largest city in the country, the prevalence of hypertension was 13.9% in urban areas in the 1980s.4 The relation between diet and blood pressure (BP) or hypertension has been the focus of substantial investigation efforts for several decades.5–7 High

Correspondence: Dr Gang Hu, Department of Physiology, University of Kuopio, PO Box 1627, 70211, Kuopio, Finland. E-mail: hu얀messi.uku.fi Received 14 July 2000; revised 4 January 2001; accepted 14 February 2001

intake of sodium, low intake of potassium and high urinary sodium-to-potassium ratio are related to high BP.8 A very high intake of sodium has been identified in Tianjin in national or international studies.9–11 Tianjin was the centre in the Intersalt study which had the highest recorded sodium and sodium-to-potassium ratio excretion of all 52 centres.8,11 The other dietary factors including calcium, magnesium, total fat intake, dietary essential fatty acids, fibre, protein, cholesterol, and alcohol consumption may influence BP, but the relationships are less well understood.6,12,13 The non-dietary factors, age, body mass index (BMI), obesity, socioeconomic status, tobacco use, family history, physical activity and psychosocial stress are associated with BP.14–16 The Tianjin Project is the first major project aiming at prevention and control of chronic diseases in China and was launched in 1984.4 We carried out two independent cross-sectional surveys in 1989 and 1992. The population survey provided an opportunity for us to assess dietary and non-dietary risk factors of different BP patterns. The aim of this article is to clarify the main dietary and non-dietary risk factors between hypertension and normal BP in a Chinese urban population.

Risk factors of hypertension in Chinese people G Hu and H Tian

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Materials and methods The baseline survey was carried out in 1989 and follow-up survey in 1992. These surveys were crosssectional studies. The city of Tianjin has a population of 9.5 million, of whom 4 million people live in the six urban districts. Random stratified cluster sampling was employed in these surveys. First, streets were selected from the six districts. Then, resident sections in each street were chosen for the survey. Finally, individuals were drawn from the local population registers in the sampled resident sections. A total of 1550 subjects completed the survey in 1989 and 2317 subjects in 1992. The age range of two surveys was 15–64 years. The response rates were 97% in 1989 and 96% in 1992. We divided the population into two groups by BP. In the normal BP group, there were 274 men, and 281 women in 1989, and 349 men and 402 women in 1992. In the hypertension group, there were 166 men, 186 women in 1989, and 201 men and 209 women in 1992. The total numbers of normal BP were 623 men, 683 women, and hypertension were 367 men and 395 women, respectively. The present analysis covered people aged 35–64 years. The surveys included nutrition survey, a selfadministered questionnaire and an anthropometric measurement. The questionnaire mainly dealt with aspects of health status, health behaviour and health knowledge. Physical activity and family history of hypertension were assessed only in 1989. Height, weight and BP were measured. The data were collected using the same methods in 1989 and 1992. Health workers carried out the measurements. All observers were intensively trained before the field survey. The methods used for assessing the diet were food weighing plus 3-day food records. Details of the dietary methods have been published.17 The collection of data was carried out by well-trained health care workers. Standardised weighing scales of 5 kg (accuracy 0.01 kg) were used for weighing most of the foods, and weighing scales of 0.5 kg (accuracy 0.001 kg) were used for weighing salts, monosodium glutamate, and sodium carbonate. The survey started by measuring and recording all foods in each household including raw materials, processed foods and home production after supper on the first day of the survey. Then individual food intake was recorded for 3 consecutive days. A single amount was used for each person to record food intake data; however, for the foods shared with others at home, the amounts were collected by estimating portion size using the bowls and plates. Health workers visited the households after supper on the second day of the survey. They checked individual food records and recorded foods bought during the days. On a 24h recall basis, the health workers collected the data from the persons who ate at home but did not keep food records. Food waste was estimated whenever weighing was not possible. The same procedure was

Journal of Human Hypertension

repeated for 3 days. All foods were weighed again on the fourth day of the survey after collecting the third-day food records. The total individual food estimations were reconciled with the food-weighing data through adjusting the sum of the 3-day food records according to the weighed household consumption of supplies. For instance, according to the food record data, a total of 3 kg of cabbage was consumed by two persons in one household, one person consuming 1 kg, the other eating 2 kg; but according to the food weighing results, a total of only 2.4 kg cabbage was consumed, not 3 kg. The extra 0.6 kg cabbage was reduced proportionately from the amount of individual consumption. Therefore, the final results for cabbage consumption were 0.8 kg for one person and 1.6 kg for the other. Intakes of energy and nutrients were analysed using the Chinese Food Composition Tables.18 Height and weight measurements were taken using a stadiometer and beam balance scale with subjects wearing usual light indoor clothing without shoes. Height and weight were measured twice, and the mean values of the readings were used for the analysis. BMI was calculated by dividing the subject’s weight (kg) by the square of the height (m). Overweight was defined as BMI ⭓25. BP was measured from the right arm using a standard mercury sphygmomanometer after 5 min of rest with the subject in the sitting position. Following the WHO MONICA Project methodology, BP was measured twice, and the mean of the two BP measurements was used for the analysis. Hypertension was defined as SBP ⭓140 mm Hg and/or DBP ⭓90 mm Hg, or diagnosed by doctors. Smoking was assessed using a set of questions in the self-administered questionnaire. Based on the response, the participants were classified into two categories: (1) current smokers, persons who had smoked regularly and smoked at least one cigarette on average each day during the past 30 days; (2) the rest people were considered as ex-smokers and never smokers. Alcohol consumption was calculated from the food intake data and converted into milliliters of absolute alcohol per day. Demographic information included age, education (0–6 years, 7–12 years, ⬎12 years), income (low, medium, high). Family history of hypertension was defined as a history of whose grandparents, parents, brothers and sisters were once diagnosed as hypertension. Physical activity was assessed using a questionnaire. Physical activity included occupation, commuting and leisure time physical activity. MET values (metabolic equivalents = activity energy expenditure divided by resting energy expenditure) from recent compendium reports were used.19 The subjects reported their occupational activity according to three-class divisions: sedentary was physically very easy, sitting office work, intermediate was work including standing and walking, and active was strenuous work. Daily work physical activity


MET index was obtained from the product of occupational activity × 5.7 (daily working hours distributed across a week). The following MET values were used: 1.5 for sedentary and retired or housewife, 2.5 for intermediate work and 4.0 for strenuous work. The subjects were asked if they walked or bicycled to and from work, school and shopping, and the duration of the above activity. The duration was coded as 0 h (used bus or no commuting physical activity), 0.13 h (1–14 min/d), 0.25 h (1–29 min/d), 0.37 h (15–29 min/d), 0.62 h (15–59 min/d), 0.75 h (30–59 min/d) and 1.25 h (⭓60 min/d). The daily MET index for ‘going to and from work’ was obtained from the product of duration × 3.5 MET, and distributed across the week by multiplying by 0.71. Leisure time sports per week was classified into two categories: ⬎1 time, and ⬍1 time or none. The data were analysed using the SPSS program. The differences of dietary factors between hypertension and normal BP people were tested by using general factorial ANOVA (adjusted for age, BMI, energy and time of survey). To assess the relationship between hypertension and dietary and non-dietary risk factors, adjusted odds ratios (OR) were calculated by logistic regression. Analysis of association between hypertension and dietary factors was adjusted for age, BMI, energy and time of survey. When calculating the OR for risk factors between different levels of categorical variables, dummy variables were created by using lowest group as reference category ie, low education, low income, no smoking, no family history, normal weight, less than one leisure time sports.

Results The descriptive characteristics of the study sample are presented in Table 1. After adjustment for age, BMI, energy and survey-period, the average daily intakes of major nutrients among hypertension and normal BP groups are shown in Table 2. The whole population had high mean daily intake of sodium. Intake of sodium was 5709–6535 mg (as NaCl 14.3– 16.3 g). Hypertensive group had higher mean values of daily sodium intake than normal BP group (P ⬍ 0.05). Hypertensive men and women had higher dietary sodium-to-potassium ratio than normotensive group. The difference was significant in women (P ⬍ 0.01), almost significant in men (P = 0.057). Low intakes of calcium and potassium were found in the whole population. There were no significant differences of mean daily intakes of other nutrients and percentages of energy coming from carbohydrate, protein and fat. The percentage of total energy from fat was more than 30%, and the intake of cholesterol was 400 mg in the whole population. Dietary covariates were entered in logistic regression model to explain the risk factors of hypertension (Table 3). Dietary sodium intake and dietary sodium-to-potassium ratio were positively associa-

ted with BP. Univariate OR for dietary sodium, dietary sodium-to-potassium ratio were 1.07 (P ⬍ 0.05), 1.12 (P = 0.061) in men, and 1.07 (P ⬍ 0.05), 1.18 (P ⬍ 0.01) in women, respectively. Age, BMI had positive association with BP, the odds ratio (OR) of hypertension for age and BMI were 1.09, 1.18 in men (P ⬍ 0.001), and 1.08, 1.16 in women (P ⬍ .0.001), respectively (Table 4). Women with high level of education were less likely to be hypertensive compared with low level of education (P ⬍ 0.05 for trend). Overweight men were 3.14 times more likely to be hypertensive (P ⬍ 0.001) compared with normal weight men. Overweight women showed 3.23 times the same risk (P ⬍ 0.001). Men with family history of hypertension had a nearly 60% increased probability to hypertension compared with men of no family history (P ⬍ 0.05), women with family history had 120% increase in probability (P ⬍ 0.001). Men going to and from work on foot or by bicycle were inversely associated with BP (OR 0.80, P ⬍ 0.05). Income, smoking, alcohol consumption, occupational and leisure time physical activity were not significantly associated with hypertension.

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Discussion Most of studies in the relationship between BP and electrolytes have used either dietary intake or urinary excretion data. Dietary and urinary sodium, urinary sodium-to-potassium ratio were significantly and positively correlated with BP, dietary and urinary potassium were inversely related to BP.8,13,16,20–23 Some Chinese investigations have indicated that average BP, dietary and urinary sodium, and urinary sodium-to-potassium ratio were consistently higher in the north than in the south of China,2–3,23 and dietary sodium-to-potassium ratio was positively correlated with BP.24,25 In the analysis of this study, we noticed an association between dietary variables and different BP patterns. The present study showed a high sodium and low potassium consumption level in the whole population, which was agreed with the results of previous Chinese surveys and the Intersalt study.9–11,22 There were higher dietary sodium intake and dietary sodium-to-potassium ratio in the hypertensive group than normal BP group. The dietary potassium intake showed no differences between hypertension and the normal BP population, but this Chinese population had lower potassium intake than desirable. The present survey indicated that dietary sodium intake and sodium-to-potassium ratio were positively associated with high BP. High level dietary sodium intake, low potassium intake and higher dietary sodium-to-potassium ratio may be major dietary risk factors in hypertension. No significant associations were found between dietary intake of calcium, magnesium, total fat, saturated fat, sodiumto-potassium ratio, protein, cholesterol and different BP patterns. The daily calcium intake was lower Journal of Human Hypertension


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Table 1 Descriptive characteristics among hypertensiona and normal BP populations in urban Tianjin, China Men

Subjects Age (years) Body mass index (kg/m2) Diastolic BP (mm Hg) Systolic BP (mm Hg) Education (%) 0–6 (years) 7–12 (years) 13+ (years) Income (%) Low Medium High Smoking (%) Alcohol consumption (%) Overweightc (%) Subjects Family history of hypertension (%) Occupation activity (MET)d Commuting physical activity (MET) Leisure time sports/per week (%) ⬎1 time ⬍1 time or no

Women

Normotension

Hypertension

Normotension

Hypertension

623 47.4 (8.6)b 23.4 (3.2) 75.9 (7.3) 117.6 (7.2)

367 54.1 (8.2) 25.7 (4.2) 91.9 (10.1) 148.8 (17.8)

683 47.4 (8.6) 24.0 (4.0) 74.7 (6.9) 117.1 (11.4)

395 54.1 (8.2) 26.2 (4.0) 90.6 (10.6) 150.7 (20.1)

21.5 63.5 15.0

33.2 54.8 12.0

35.6 57.2 7.2

61.1 35.1 3.8

30.3 35.4 34.3 65.3 26.6 30.7 274 45.6 15.1 (7.0) 1.5 (1.0)

24.7 35.5 39.8 57.2 27.7 57.8 166 48.6 13.0 (6.3) 1.1 (1.0)

27.4 38.8 33.8 25.3 2.8 33.8 281 44.8 14.5 (6.9) 0.9 (0.9)

33.5 30.3 36.2 29.0 3.8 63.4 186 51.1 14.8 (6.9) 0.7 (0.8)

20.4 79.6

23.5 76.5

13.9 86.1

11.8 88.2

Hypertension was defined as systolic BP ⭓140 mm Hg and/or diastolic BP ⭓90 mm Hg, or diagnosis by doctors. Mean (standard deviation). c Overweight was defined as body mass index ⭓25. d MET, metabolic equivalents. a

b

Table 2 Adjusted means (s.e.) daily intake of some nutrients among hypertensiona and normal BP populations in urban Tianjin, Chinab Men

Energy (kcal) Protein (g) Total fat (g) Carbohydrate (g) Saturated fat (g) Fibre (g) Sodium (mg) Potassium (mg) Na/K ratio Calcium (mg) Magnesium (mg) Cholesterol (mg) Protein (% energy) Fat (% energy) Carbohydrate (% energy) a

Women

Normotension

Hypertension

P values

Normotension

Hypertension

P values

2599 (25) 90 (1) 89 (1) 357 (2) 20 (0.4) 14 (1) 6190 (93) 2201 (25) 2.99 (0.0) 529 (10) 375 (4) 443 (16) 14.0 (0.1) 30.4 (0.3) 55.6 (0.3)

2563 (34) 90 (1) 90 (1) 353 (3) 20 (0.5) 13 (2) 6535 (124) 2190 (28) 3.13 (0.1) 535 (13) 380 (6) 437 (21) 14.0 (0.2) 31.0 (0.4) 55.0 (0.5)

0.274 0.998 0.276 0.278 0.408 0.464 0.039 0.837 0.057 0.762 0.405 0.944 0.983 0.390 0.401

2200 (21) 76 (1) 77 (1) 299 (2) 19 (0.5) 12 (1) 5709 (84) 1939 (18) 3.08 (0.1) 477 (10) 333 (3) 425 (17) 13.9 (0.1) 31.2 (0.3) 54.9 (0.3)

2192 (28) 76 (1) 77 (1) 301 (2) 18 (0.6) 11 (1) 6011 (111) 1895 (24) 3.34 (0.1) 452 (13) 327 (5) 419 (21) 13.9 (0.1) 31.0 (0.4) 55.1 (0.4)

0.765 0.633 0.670 0.565 0.195 0.225 0.048 0.124 0.004 0.170 0.303 0.834 0.880 0.615 0.585

Hypertension was defined as systolic BP ⭓140 mm Hg and/or diastolic BP ⭓90 mm Hg, or diagnosis by doctors. Analyses use general factorial ANOVA model. Age, energy, body mass index and time of survey were adjusted.

b

(452–535 mg), cholesterol intake was higher (⬎400 mg), and the percentage of total energy from fat was more than 30% in the whole population. It has been suggested that the recommendation for Chinese subjects would be an intake of more than 800 mg calcium and 20–25% of total energy from fat per day.26 WHO recommends an intake of less than Journal of Human Hypertension

300 mg cholesterol and 15–30% of total energy from fat per day.27 Food weighing and consecutive 3-day food records were used in the present study to assess nutrients intake, which provided a more accurate estimate of individual intake compared with 24-h food records only. The limitation of collection of dietary


Table 3 Adjusted univariate odds ratios (OR) and 95% confidence intervals (CI) for dietary factors among hypertensiona and normal BP populations in urban Tianjin, Chinab Men

Energy (1000 kcal) Protein (g) Total fat (g) Carbohydrate (g) Saturated fat (g) Fibre (g) Sodium (g) Potassium (g) Na/K ratio Calcium (mg) Magnesium (mg) Cholesterol (mg) Protein (% energy) Fat (% energy) Carbohydrate (% energy) Alcohol (yes vs no) a

491

Women

OR

95% CI

P values

OR

95% CI

P values

0.87 1.00 1.00 1.00 1.13 1.00 1.07 0.98 1.12 1.00 1.00 1.00 0.99 1.01 1.00 0.99

0.69–1.09 1.00–1.01 1.00–1.01 1.00–1.00 0.83–1.55 0.99–1.01 1.00–1.13 0.79–1.21 0.99–1.26 1.00–1.00 1.00–1.00 1.00–1.00 0.97–1.01 0.99–1.03 0.95–1.05 0.54 –1.85

0.362 0.963 0.271 0.267 0.429 0.576 0.040 0.840 0.061 0.805 0.639 0.816 1.000 0.373 0.383 0.101

0.97 1.00 1.00 1.00 0.82 0.99 1.07 0.80 1.18 1.00 1.00 1.00 1.00 0.99 1.00 0.67

0.76–1.25 0.99–1.01 0.99–1.01 1.00–1.00 0.61–1.10 0.97–1.01 1.01–1.14 0.60–1.08 1.06–1.30 1.00–1.00 1.00–1.00 1.00–1.00 0.99–1.02 0.98–1.01 0.95–1.05 0.19–2.33

0.872 0.654 0.651 0.558 0.193 0.257 0.047 0.118 0.005 0.187 0.422 0.775 0.916 0.630 0.609 0.373

Hypertension was defined as systolic BP ⭓140 mm Hg and/or diastolic BP ⭓90 mm Hg, or diagnosis by doctors. Analyses use logistics regression. Age, energy, body mass index, and time of survey were adjusted.

b

Table 4 Adjusted odds ratios (OR) and 95% confidence intervals (CI) for non-dietary factors among hypertensiona and normal BP populations in urban Tianjin, Chinab Men

Age (years) Body mass index (kg/m2) Education (years) 0–6 7–12 13+ Trend Income Low Medium High Trend Smoking (yes vs no) Overweightc (yes vs no) Family history (yes vs no) Occupational activity (MET)d Commuting activity (MET) Leisure time sports per week ⬎1 time vs ⬍1 time or none a

Women

OR

95% CI

P values

OR

95% CI

P values

1.09 1.18

1.06–1.12 1.10–1.26

0.000 0.000

1.08 1.16

1.05–1.12 1.11–1.22

0.000 0.000

1.00 1.02 0.78 0.428

0.72–1.45 0.47–1.20

0.845 0.300

1.00 0.70 0.59 0.039

0.51–0.97 0.31–1.14

0.027 0.066

0.44 –1.25 0.54 –1.53

0.380 0.976

0.45–1.20 2.12– 4.91 1.45–3.50 0.99–1.06 0.85–1.44

0.232 0.000 0.000 0.138 0.693

0.34 –1.26

0.089

1.00 1.20 1.07 0.703 1.08 3.14 1.59 0.98 0.80

0.70–2.09 0.62–1.87

0.433 0.833

0.69–1.69 2.04 –4.83 1.03–2.45 0.95–1.02 0.63–0.99

0.728 0.000 0.048 0.703 0.044

1.00 0.74 0.91 0.586 0.74 3.23 2.26 1.03 1.10

0.86

0.51–1.45

0.604

0.66

Hypertension was defined as systolic BP ⭓140 mm Hg and/or diastolic BP ⭓90 mm Hg, or diagnosis by doctors. Analyses use logistics regression.cOverweight was defined as body mass index ⭓25. MET, metabolic equivalents.

b

d

data by this method is labour-intensive and time consuming. Since daily intake of nutrients is variable, using a cross-sectional nutritional survey may attenuate the relationships between dietary factors and BP. Individual dietary habits are influenced by a host of social, cultural, customary and economic factors, thus assessments of diet in a relatively homogeneous population may weaken or lack associations between hypertension status and many dietary variables.

Age has been positively correlated with high BP in both international and Chinese studies.14,22 The present study gave the same results. In both adolescents and adults, the correlation between BP and weight has been highly significant.28,29 In the present study, hypertensive men and women had significantly higher mean BMI than normal BP population showing a balance in energy intake and physical activity. Being overweight was positively associated with high BP in the whole population and was a Journal of Human Hypertension


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risk factor of hypertension. The results may support those of a previous study.30 The present survey indicated that a family history of hypertension was a major risk factor of hypertension, because family history had an independent and positive association with high BP. Education level was inversely related with cardiovascular risk factors in several previous studies.31,32 However, the relationship was only consistent in Chinese women. Most studies have reported the associations between smoking and BP, alcohol consumption and BP.16,33 The present study found, however, no associations between smoking, alcohol consumption and different BP patterns. Some studies have reported that men in a sedentary or inactive occupation had higher DBP, SBP or arterial pressure than those in an active or higher level job.34,35 A Japanese prospective cohort study has shown that walking to work and other leisure time physical activity decreased the risk for hypertension in Japanese men.36 Several population studies have demonstrated an inverse relationship between leisure time physical activity and BP levels.37–39 The present survey indicated no relationships between both occupational and leisure time physical activity and BP levels. Commuting physical activity was inversely associated with BP levels in men and is very important to urban Chinese. More than 90% of the urban population usually use bicycle or walk to and from work, school and shopping per day.40 Very few have private cars. Regular commuting physical activity may be a protecting factor for hypertension.

Conclusion The present study has shown that there were high sodium and low potassium consumption levels in the whole of the Tianjin urban population, and the hypertensive group had a high dietary sodium intake and high dietary sodium-to-potassium ratio. Age, BMI, overweight, family history of hypertension, dietary sodium intake, and dietary sodium-topotassium ratio were positively associated with high BP. Education level in women and commuting physical activity in men were inversely associated with high BP.

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