Medical, Socialogical and environmental issues in cardiovascular disease epidemiology, prevention and rehabilitation.
AK Sharma, VP Gupta, H Prakash, H Bharadwaj, Rajeev Gupta
Monilek Hospital and Research Centre, Jaipur; and University of
Rajasthan, Jaipur 302004 India
To determine the prevalence of hypertension in a desert-based rural population we conducted a total community cross-sectional survey in Rajasthan. 3148 persons (1982 males and 1166 females) aged20 years were examined in a cluster of three villages. A doctor-administered questionnaire, physical examination and electrocardiogram was performed. These individuals were grouped according to the World Health Organisation guidelines for diagnosis of hypertension (systolic BP140 and/or diastolic BP90 mm Hg or known hypertensives. Prevalence of hypertension was 23.7% in males and 16.9% in females. In age-groups 20-29, 30-39, 40-49, 50-59, 60-69 and 70+ years the prevalence was: males 8%, 20%, 33%, 35%, 36% and 42% and females 7%, 15%, 23%, 29%, 26% and 53% respectively. Only 7%males and 8% females were aware of heir high blood pressure. Multivariate logistic regression analysis showed that age, illiteracy, smoking and obesity in males and age and illiteracy in females were associated with significantly greater hypertension prevalence (p<0.05). As compared to studies reported from other rural areas of India, the individuals living in the Thar desert of Rajasthan have a greater prevalence of hypertension. Role of environmental and dietary factors (extreme climate, hardness of water, salt excess, etc.) need further studies.
High blood pressure (BP) or hypertension is a major cardiovascular risk factor and leads to cerebral stroke and coronary heartdisease.1 It is also a leading cause of blindness, renal failure and congestive heart failure in developed countries. This condition is emerging as a major health problem in developing countries around the world2 and studies have reported that it is already a significant problem in urban and rural areas of India.3
Studies from Britain4 and USA5 have reported a large within-country variation in the prevalence of hypertension. In Britain hypertension prevalence is the highest in the north and the lowest in the south. This regional difference has been explained by a variety of ecological (water hardness, rainfall and temperature) and socio-economic factors. In USA hypertension prevalence is the highest in south-western states. Racial differences (more African-Americans) and socio-economic factors have been implicated. Studies from Sweden have shown influence of water hardness in determining hypertension prevlence.6 We studied hypertension prevalence in a desert-based rural population using criteria of US Fifth Joint National Committee (JNC-V) and the World Health Organisation.1,7 Ecological data were obtained from regional sources. Findings were compared with previous hypertension prevalence studies in Indian rural populations.3
A total of 3148 persons, in a cluster of three villages in Rajasthan (western India) were studied. There were 1982 males and 1166 females and comprised of 90.6% (1982 of 2188) eligible males and 59.2% (1166 of 1968) eligible females of the target population aged 20 years and more. The study was preceded by community meetings in villages with involvement of local social leaders. The subjects answered a physician-administered questionnaire on personal, socio-economic and family history and underwent detailed physical examination including a 12-lead electrocardiogram. Guidelines suggested by JNC-V1 and World Health Organisation (WHO)7 were used. The proforma recorded various social factors such as level of education and occupation. Conventional risk factors such as smoking, alcohol intake and amount of physical activity were inquired. The physical examination emphasised measurement of BP, height, weight, truncal obesity and examination of the cardiovascular system. Supine BP was measured using standardised mercury manometer. At least two readings at 5-minute intervals, as per the JNC-V guidelines, were recorded. If a high BP (140/90) was noted a third reading was taken after 30 minutes. The lowest of the three readings was taken in analysis.
Hypertension was diagnosed as per the criteria of JNC-V and WHO. Phase V of Kortakoff's sounds was taken for the determination of diastolic BP. Normal BP was defined as systolic BP <140 mm Hg and a diastolic BP <90 mm Hg. Subjects taking anti-hypertensive treatment were considered to have hypertension regardless of the measured BP. All past and current smokers and tobacco users were classified as smokers. Criteria for classification of body-mass index, obesityand physical activity have been reported.8
Table 1: Blood Pressure Levels in Rural Men (n=1982)
Age-group Numbers Mean Median Skew
Systolic BP
20-29 571 122±9 120 2.39±0.1
30-39 495 125±11 126 1.75±0.1
40-49 366 129±11 128 1.47±0.1
50-59 268 130±16 128 1.54±0.2
60-69 204 133±20 130 2.32±0.2
70± 78 134±20 130 1.26±0.3
ANOVA F=36.7; r=0.29, r2=0.08; b=2.71±0.20; p<0.001
Diastolic BP
20-29 571 78±6 78 -0.24±0.1
30-39 495 81±7 80 0.29±0.1
40-49 366 83±9 84 0.35±0.1
50-59 268 83±9 83 0.36±0.1
60-69 204 84±10 82 1.08±0.2
70± 78 84±9 84 0.42±0.3
ANOVA F=31.1; r=0.25, r2=0.06; b=1.34±0.12; p<0.001
Statistical analysis: Mean, standard deviation, median and percentile distribution of systolic and diastolic BP in males and females at different age-deciles were calculated. Inter-group differences were evaluated by analysis of variance (ANOVA). Correlation coefficients (r) were determined for age with BP levels. Regression coefficients (b) were calculated for BP with age-deciles to determine change in BP with increasing age. The prevalence rates are given in percent. To determine significant associations of hypertension risk factors with its prevalence, logistic regression analysis was performed using SPSS statistical package (SPSS Inc., Chicago, USA, version 4.0.1). Dependent variable was presence or absence of hypertension and independent variables were age, years of education, smoking, physical activity and body-mass index. Variables of smoking and physical activity were dichotomised (yes=1, no=0) and others used as continuous variables. Odds ratios and 95% confidence intervals were determined. Two-tailed p values <0.05 were considered significant.
Table 2: Blood Pressure Levels in Rural Women (n=1166)
Age-group Numbers Mean Median Skew
Systolic BP
20-29 382 119±9 120 1.45±0.1
30-39 342 124±11 122 1.43±0.1
40-49 212 127±15 126 1.96±0.2
50-59 127 130±18 126 1.51±0.2
60-69 80 127±17 128 2.05±0.3
70± 23 134±19 130 0.39±0.5
ANOVA F=21.4; r=0.27, r2=0.07; b=2.70±0.28; p<0.001
Diastolic BP
20-29 382 77±6 76 1.29±0.1
30-39 342 79±7 78 0.55±0.1
40-49 212 81±8 80 0.63±0.1
50-59 127 83±9 82 0.42±0.2
60-69 80 81±8 81 9.35±0.3
70± 23 85±11 84 0.40±0.4
ANOVA F=20.1; r=0.27, r2=0.07; b=1.52±0.16; p<0.001
The mean and median BP values in males and females are shown in Tables 1 and 2. The median values for systolic and diastolic BP are lower than mean values suggesting a positive skew of its distribution in both males and females. Age-group specific systolic and diastolic BP values are also shown in Tables 1 and 2. There is a significant increase in both systolic and diastolic BP with age (ANOVA, F>20.00, p<0.0001). Increase in BP levels with age is confirmed by correlation analysis. There are significant r values for both systolic and diastolic BP in rural men and women (r value: systolic BP: males 0.27, females 0.27; diastolic BP: males 0.25, females 0.27, p<0.001). r2 which signifies variance of BP with age is also significant (systolic BP: males 0.08, females 0.07; diastolic BP: males 0.06m females 0.07, p<0.001). Regression analysis confirmed the significant association of BP with age. Regression coefficient (b) was significant in both the groups and showed that there was an increase in systolic BP by 2.71±0.2 mmHg in males and by 2.70±0.3 mmHg in females and in diastolic BP by 1.34±0.1 mmHg in males and by 1.52±0.2 mmHg in females with each decadal increase in age.
Table 3: Age-specific Distribution of Persons with Hypertension
Age-group Males (n=1982) Females (n=1166) Total (n=3148)
  Total Patients Total Patients Total Patients
20-29 571 47(8) 382 27(7) 953 74(8)
30-39 495 101(20) 342 52(15) 837 153(18)
40-49 366 120(33) 212 48(23) 578 168(29)
50-59 268 95(35) 127 37(29) 395 132(33)
60-69 204 74(42) 80 21(26) 284 95(33)
70+ 78 33(42) 23 12(52) 101 45(44)
Total 1982 470(24) 1166 197(17) 3148 667(21)
Numbers in parentheses are percent.
The overall prevalence of hypertension using the criteria of either the systolic BP140 and/or diastolic BP>90 mmHg or hypertensives on treatment was 24% in males and 17% in females. There was an age-dependent increase in the prevalence of hypertension in both males and females (Table 3) with a low prevalence of hypertension in younger age groups and a high prevalence in older persons. Only 7.0% of males and 8.1% of female hypertensives were aware of their hypertension. However, 73% of the persons who were aware of their hypertension were on some form of drug therapy. When classified according to the older WHO criteria (160/95 mmHg) used by most of the previous Indian studies, the hypertension prevalence was 7.6% in males and 6.2% in females.
Table 4: Multivariate logistic regression analysis of hypertension with various risk factors
Risk Factor Males Females
  Odds ratio (95% CI) P value Odds ratio (95% CI) P value
Age 1.04 (1.03, 1.05) <0.001 1.04 (1.02, 1.05 <0.001
Education (yr) 0.94 (0.89, 0.99) 0.023 0.93 (0.87, 0.98) 0.015
Smoking 1.26 (1.01, 1.58) 0.043 1.06 (0.52, 2.16) 0.866
Physical activity 0.77 (0.56, 1.04) 0.093 0.29 (0.12, 0.68) 0.005
Body mass index 1.11 (1.07, 1.15) <0.001 1.10 (0.98, 1.02) 0.672
Constant -5.5033 <0.001 -3.0033 <0.001
Univariate analysis showed that illiteracy was significantly associated with hypertension. No significant relationship emerged with alcohol intake and physical activity on univariate analysis. Multivariate logistic regression analysis showed that age and low level of education in both males and females, and smoking and higher body-mass index in males were risk factors for hypertension prevalence (Table 4).
This study shows that there is a high prevalence of hypertension in a desert-based rural Indian population. According to the recently suggested JNC-V1 and WHO7 guidelines the overall prevalence of hypertension is 23.7% in males and 16.9% in females. According to the older WHO criteria9 the prevalence is 7.6% in males and 6.2% in females.
Studies from developed countries have reported that smoking, alcohol consumption, obesity and low socio-economic status as suggested by low level of education are associated with greater prevalence of hypertension.1 Similar results are seen in the present study conforming that these factors are equally important in developing countries as in the developed.
The International Clinical Epidemiology Network (INCLEN) data10 using the older WHO criteria reported that prevalence of hypertension in developing countries varied from a low of 3% in rural Thailand and 5% in rural China to a high of 22% in the Philippines and 23% in Indonesia. The data also showed that the prevalence of hypertension was more than 20% among 6 of the 12 communities studied in different countries of Asia and Latin America. In developed countries, viz. USA, the prevalence of hypertension in adults is about 40%1 which is much higher than the present study.

Studies from rural areas of developing countries have been reported in a WHO publication2 and show that the prevalence of hypertension using the older WHO criteria varied from 2-15% in different countries. The prevalence of hypertension in rural areas of Ethiopia (males 6%, females 2%), Zulu (males 7%, females 14%), Tanzania (males 2%, females 2%), Zambia (males 8%, females 10%), Nepal (males 8%, females 4%), and Tibet (males 12%, females 15%) show a wide geographic variation. Most of the studies among Indian rural populations using the older WHO criteria (BP160/95) have reported lower prevalence of hypertension. Recent studies have reported prevalence of 2.5% to 5.5% in Haryana (Gupta et al, Wasir et al),11,12 Punjab (Sharma et al),13 and Maharashtra (Joshi et al, Jajoo et al)14,15 which are significantly lower than our study. Gilberts et al17 reported a very high prevalence in a south Indian rural population. This high prevalence could be due a reflection of semi-urban nature of the rural population in Kerala.18

Studies in desert based rural populations in Rajasthan have consistently shows high prevalence of hypertension. Baldwa et al19 studied 912 rural subjects aged 21-60 years in Jaipur district, which is on the margin of the Thar desert and reported hypertension in 7.89% with a higher prevalence in females (8.81%) as compared to men (6.93%). Kumar et al20 studied 6840 rural subjects in Churu district of Rajasthan which is in the heart of Thar desert and reported a prevalence of 3.83%, more in men (4.01%) than in women (3.62%). Hussain et al21 studied 5142 subjects aged 20-70 years in Bikaner district also in Central Thar desert and reported hypertension in 6.67%, men (6.17%) had a lower prevalence than women (7.32%). Our study which has been performed in Nagaur district in the central Thar desert also shows a high prevalence of hypertension and is comparable to other Rajasthan studies.

Regional variation in hypertension prevalence has been well studied in Europe and Britain. In Europe the highest prevalence is seen in the Nordic countries which are close to the North Pole and the lowest prevalence is seen in the Mediterranean countries that are warmer in comparison.22 Environmental factors such as low temperature are suggested explanations. Similar pattern in seen in Britain where hypertension prevalence is the highest in cooler Scotland and the lowest in Wales and south-east England.4 In the US a high prevalence of hypertension in south-eastern states is considered to be due to greater number of African-Americans settled there.5 A recent study has reported a higher prevalence of hypertension in Europe as compared to the USA. Mean BP was 136/83 mmHg in European countries and 127/77 in Canada and USA and there was a 60% higher prevalence of hypertension. The cause of this difference is not known.23

Rajasthan is a desert state and the mean temperature is higher than in the states of Punjab, Haryana and Maharashtra. Higher temperatures should be associated with lower hypertension prevalence, therefore, atmospheric temperature does not explain the excess. Annual rainfall and relative humidity which have a negative correlation with hypertension prevalence, is considerably lower in Rajasthan as compared to other states and maybe important. Water hardness is also considered an important factor in determining hypertension prevalence. However, water hardness in states of Rajasthan, Punjab, Haryana and Maharashtra is almost similar.

Sodium content of the diet is an important predictor of hypertension.24 Populations with negligible sodium intake have very low blood pressures. Surveys have shown a high salt intake in Rajasthan.25 Urinary sodium content as indicator of its intake in a tribal population in Orissa was studied by Dash et al.26 They studied 4523 tribal subjects and reported hypertension in 0.44%. Daily urinary sodium excretion in a random sample of this population was 35-75 mEq in 86.3%, 76-100 mEq in 7.2% and more than 100 mEq in 6.3% while hypertensives had a mean sodium excretion of 120.7 mEq. Sodium content of diets in populations of other states is not known and needs further studies to explain the regional differences in hypertension prevalence.
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