| RECENT TRENDS IN HYPERTENSTION EPIDEMIOLOGY IN INDIA | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Rajeev Gupta | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Department of Medicine, Monilek Hospital and Research Centre, Jawahar Nagar; and Mahatma Gandhi National Institute of Medical Sciences, Sitapura; Jaipur 302004 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Cardiovascular diseases caused 2.3 million deaths in India in the year 1990, this is projected to double by year 2020. Hypertension is directly responsible for 57% of all stroke deaths and 24% of all coronary heart disease deaths in India. Indian urban population studies in mid 1950s used older WHO guidelines for diagnosis (BP 160 and/or 95 mm Hg) and reported hypertension prevalence of 1.2 to 4.0%. Subsequent studies report steadily increasing prevalence from 5% in 1960's to 12-15% in 1990's. Hypertension prevalence is lower in rural Indian population although there has been a steady increase over time here as well. Recent studies using revised criteria (BP140 and/or 90 mm Hg) have shown high prevalence of hypertension among urban adults: men 30%, women 33% in Jaipur (1995), men 44%, women 45% in Mumbai (1999), men 31%, women 36% in Thiruvananthapuram (2000), 14% in Chennai (2001), and men 36%, women 37% in Jaipur (2002). Among the rural populations hypertension prevalence is men 24% , women 17% in Rajasthan (1994). Hypertension diagnosed by multiple examinations has been reported in 27% male and 28% female executives in Mumbai (2000) and 4.5% rural subjects in Haryana (1999). |
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| There is a strong correlation between changing lifestyle factors and increase in hypertension in India. The nature of genetic contribution and gene-environment interaction in accelerating the hypertension epidemic in India needs more studies. Pooling of epidemiological studies shows that hypertension is present in 25% urban and 10% rural subjects in India. At an underestimate there are 42 million hypertensives in rural and 45 million in urban populations. 70% of these would be Stage I hypertension (systolic BP 140-159 and/or diastolic BP 90-99 mm Hg). Recent reports show that borderline hypertension (systolic BP 130-139 and/or diastolic BP 85-89 mm Hg) and stage I hypertension carry a significant cardiovascular risk and there is need to reduce this blood pressure. Population-based cost-effective hypertension control strategies should be developed. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Table 1: Cardiovascular deaths by region in the years 1990 and 2020. Global Burden of Disease Study1,2 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| GLOBAL BURDEN OF HYPERTENSION | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Cardiovascular diseases account for a large proportion of all deaths and disability worldwide. Global Burden of Disease Study reported that in 1990 there were 5.2 million deaths from cardiovascular diseases in economically developed countries and 9.1 million deaths from the same causes in developing countries.1 However, whereas about one-quarter of all cardiovascular disease deaths occurred in persons who were less than 70 years of age in the developed world, more than about half of these deaths occurred in those less than 70 years in the developing world.2 It has been predicted that by the year 2020 there will be an increase by almost 75% in the global cardiovascular disease burden. Almost all of this increase will occur in developing countries. (Table 1). | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| The situation in India is more alarming. It was reported that of a total of 9.4 million deaths in India in 1990, cardiovascular diseases caused 2.3 million deaths (25%). 1.2 million deaths were due to coronary heart disease and 0.5 million due to stroke.1 It has been predicted that by 2020 there would be a 111% increase in cardiovascular deaths in India. This increase is much more than 77% for China, 106% for other Asian countries and 15% for economically developed countries.2 Control of the predicted increase in cardiovascular diseases will require modification of risk factors that have two characteristics. First, the risk factors must have high attributable risk or high prevalence, or both. Second, most or all of the risks must be reversible cost effectively. Blood pressure (BP) is directly associated with risks of several types of cardiovascular disease, and the associations of blood pressure with disease risk are continuous, indicating that large proportions of most populations have non-optimal blood pressure values.3 Moreover, most or all blood pressure related risk appears to be reversible within a few years with inexpensive interventions. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Table 2: Indian Hypertension Prevalence Studies (BP 160/95)4 |
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| Hypertension is directly responsible for 57% of all stroke deaths and 24% of all coronary heart disease deaths in India.2 This fact is important because hypertension is a controllable disease and a 2mm Hg population-wide decrease in blood pressure can prevent 151,000 stroke and 153,000 coronary heart disease deaths in India.2 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| RECENT INDIAN STUDIES |
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| Trends in hypertension prevalence in India have been reviewed in this journal and elsewhere.4,5 Studies have shown a high prevalence of hypertension in both urban and rural areas. Prevalence rates are almost similar to those in the USA. To determine the changing trends of hypertension prevalence in Indian urban and rural populations aged 20-70 years, we evaluated previous hypertension epidemiological studies (Table 2).3-5 Indian urban population studies in the mid 1950s used the standardised WHO guidelines for diagnosis of hypertension (known hypertension or BP160 mm Hg systolic and/or 95 mm Hg diastolic) and reported hypertension prevalence of 1.2 to 4.0%. Subsequent studies report steadily increasing hypertension prevalence- 4.35% in Agra (1961), 6.43% in Rohtak (1975), 15.52% in Bombay (1980), 14.08% in Ludhiana (1985), 10.99% in Jaipur (1995), 11.59% in Delhi (1997), 13.1% in Chandigarh (1999) (x2 for trend= 5.99, p=0.014). Statistical analysis shows a significant positive trend confirmed by non-parametric analysis (Mantel-Haenszel test, p=0.014) as well as regression analysis (r=0.70, p=0.026). |
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| Although there is generally a lower prevalence of hypertension in rural Indian population, there has been a steady increase over time in this rural population as well. It has also increased over the years- 0.52% in Bombay (1959), 1.99% in Delhi (1959), 3.57% in Haryana (1978), 5.41% in Delhi (1983), 5.59% in Rajasthan (1984), 2.63% in Punjab (1985), 4.02% in Maharashtra (1993), 3.41% in Maharasthtra (1993), 7.08% in Rajasthan (1994) and 3.58% in Haryana (1998) (x2 for trend= 2.75, p=0.097). In South Indian rural subjects, that are almost urbanised, the prevalence has been reported to be as high as 17.8% (1993) and 12.46% (1994) in recent years. Overall there is a significant increase in hypertension prevalence in rural areas although the rise is not as steep as in urban populations (r=0.67, p=0.025). On comparison of mean levels of BP from 1942 to 1995 it is seen that in urban men aged 40-49 years there is a significant increase in systolic BP (r=0.95, p<0.001) but not in diastolic (r=0.43, p>0.2). This is of obvious clinical significance in light of the recent evidence that systolic BP is more closely linked to cardiovascular events and cardiac mortality.6 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Systolic BP140 mm Hg and/or diastolic BP90 mm Hg is the currently accepted dividing line based on epidemiological and intervention studies.7 This level has been shown to be associated with increased cardiovascular risk in prospective cohort and case-control studies in USA and Europe. Framingham study reported that there was a continuum of risk of stroke and coronary heart disease with increasing diastolic BP and the levels where risks were not present were unknown.8 Stamler et al analysed US studies of correlation of BP levels with cardiovascular risks and showed that both systolic and diastolic BP have continuous, graded, strong, independent, and etiologically significant relationship to the outcome variables such as cardiovascular mortality and all-cause mortality.9 |
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| Table 3: Recent Indian Hypertension Prevalence Studies (BP140/90) |
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| No prospective studies similar to Framingham or other studies exist among Indians and therefore the level of BP where risk of cardiovascular events increase is not well defined. Most of the studies from developing countries show a lower mean population BP as compared to developed countries.10-12 Therefore, the population norms as well as the values above which high BP causes vascular risk could be lower in these countries.12 However, in absence of prospective data and also because of the current recommendations of World Health Organisation7 and many Indian Consensus Groups we shall accept the criteria of systolic140 mm Hg and/or diastolic90 mm Hg as cut-off level for diagnosis of hypertension. |
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| In this article we shall focus on recent Indian studies (Table 3). The prevalence of hypertension defined by recent World Health Organisation criteria has been reported among some urban Indian populations. Gupta et al (1995)13 reported hypertension in Jaipur in 30% men and 33% women aged20 years. Gupta et al (1999)14 reported hypertension in 44% men and 45% women in Mumbai, Joseph et al (2000)15 reported it in 31% men and 41% women in Trivandrum, while Mohan et al (2001)16 reported an age-adjusted prevalence of 14% in Chennai. Gupta et al (2002)17 reported its prevalence in 36% men and 37% women in Jaipur. Anand (2000)18 reported hypertension in 34.1% middle-class executives in Mumbai but after multiple blood pressure measurements it was confirmed in 26.8% male and 27.6% female officers. These findings are in consonance with other regions of Asia where it has been reported that, at any one time, about half of all individuals have high blood pressure.2 |
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| Among the rural populations hypertension prevalence using recent criteria was first reported by Gupta et al (1994)19 in subjects aged 20 years. Hypertension was present in 24% men and 17% women. Prevalence of hypertension diagnosed on the basis of multiple blood pressure measurements was reported by Malhotra et al (1999)20 who reported it in 3.5% men and 5.8% women in Haryana adults aged 16-70 years; this low prevalence was attributed to very low body-mass index in this population. |
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| Figure 1: Age-specific hypertension prevalence (%) in an urban Indian population in years 199513 and 200217. No significant change in the prevalence at any age-group is observed (p >0.05). | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Is hypertension prevalence increasing in India? Meta-analysis of previous Indian prevalence studies has shown that there has been a significant increase in hypertension in both urban and rural areas (Table 2). This increase is associated with increasing mean systolic blood pressure levels. These studies were widely distributed in time and the methodologies were different. Observer bias cannot be excluded. We performed successive cross sectional studies to determine the change in blood pressure levels and hypertension prevalence in Jaipur.13,17 In 1995, the overall prevalence of hypertension in adults >20 years was 30% in men and 33% in women while in 2002 the age-adjusted prevalence is 30% in men and 34% in women (p=n.s.). Age-specific prevalence rates are shown in Figure 1 and no significant differences are seen. These results show that over a short-term of 7 years there is no significant change in hypertension prevalence in an urban Indian population. The mean blood pressure levels also did not change.12,17 Possibly a longer time is needed to effect changes in a given population. Prospective cohort studies within a population are needed to answer these questions as multiple factors are involved in hypertension variation in epidemiological studies. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| GENETIC OR ENVIRONMENTAL INFLUENCES |
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| Although the precise reasons for the increase in hypertension prevalence among Indians is not established, several possibilities exist. Studies among the unacculturated societies have shown lower BP levels that are not influenced by age.21 Data show that among the so-called unacculturated and less-cultured Indian rural populations there is only a small increase in prevalence in hypertension over the years.4 On the other hand, in urban populations that are being exposed to stress of acculturation and modernisation, the hypertension prevalence rates have more than doubled in the last 30 years. Important hypertension risk factors are genetic and environmental (Table 4). There are a large number of genes that are responsible for hypertension. Single-gene-related hypertension is, however, rare. Intermediate phenotypes are more important and prevalent than gene mutations. These phenotypes are familial dyslipidaemia, metabolic syndrome, insulin resistance, body-fat distribution, kallikrein deficiency, sodium sensitivity, nonmodulation of aldosterone and renal blood flow, abnormal cellular ion transport systems (Na, Li, K, H transport systems), and blood pressure reactivity. The nature of genetic contribution to hypertension needs more studies among Indians.3 Population and animal studies suggest a polygenic or oligogenic model for hypertension wherein susceptibility imparted by any single gene is modest and quantitative.21 Such genetic variations would be expected to modulate response to environmental exposure and may only achieve significance through cumulative integration of lifetime experiences. Although this scenario greatly complicates the task of genetic epidemiologists, major studies are currently under way and are likely to produce a list of common genes contributing to hypertension. Essential hypertension may be considered the result of interactions between genes and environment.4,22 The environmental effects are powerful and explain most of the BP differences between populations.22 Obesity, especially truncal obesity, is a powerful influence because of the associated insulin resistance that often leads to cardiovascular dysmetabolic syndrome and is associated with hypertension. Other important environmental factors are smoking, alcohol intake, physical inactivity, dietary excess of sodium and fat and deficiency of potassium and fibre intake, and psychosocial stress. There is epidemiological evidence that population demographic changes in India have increased hypertension risk factors. There is increasing life expectancy, urbanisation, development, and affluence in India.23 In 1901 only 11% of the population was living in an urban area; this proportion was 17.6% in 1951, 18.3% in 1961, 20.2% in 1971, 23.7% in 1981 and 26.1% in 1991. There is a strong correlation between urbanisation and increase in hypertension prevalence (r=0.92, p<0.01). Affluence as measured by evaluation of per capita net domestic product, growth of production, and human development index has also increased sharply in India in the recent years and correlates positively with the hypertension increase. Tobacco production, which is a surrogate for its consumption, is increasing at a very high rate in India. Per capita fat and oil consumption has also increased in the last 40 years. It was 5.79 kg/person/year in 1961, 5.85 in 1971, 6.48 in 1981 and 6.96 in 1987. Salt consumption was 10.7 gm/person/day in 1971 and increased to 13.0 in 1981, 15.8 in 1991 and 16.9 in 1994. We hypothesise that summation of these sociodemographic and lifestyle factors is accelerating the hypertension epidemic currently sweeping India and other developing countries. Gene-environment interaction in accelerating the hypertension epidemic needs more studies. |
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| Table 4: Hypertension Risk Factors | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| EPIDEMIOLOGICAL STUDIES AND IMPLICATIONS FOR TREATMENT |
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| The Treatment of Mild Hypertension Study (TOMHS)24 showed that lowering of mildly raised BP (Stage I hypertension: systolic 140-159 and/or diastolic 90-95 mm Hg) by drugs was associated with improved outcome as compared to placebo group. In Multiple Risk Factor Intervention Trial (MRFIT)9 there was an excess of mortality at systolic BP >110 mm Hg although statistical significance was achieved at BP of >120 mm Hg. Stamler (1992)25 commented that an average population systolic BP of 110 mm Hg is a realistic goal. In India, we need to examine the absolute numbers of patients with hypertension that would be eligible for treatment if we employ these recommendations. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Epidemiological studies have shown that hypertension is present in 25% of urban and 10% of rural subjects in India. There is a difference in measurement methodology of blood pressure in epidemiological studies as compared to clinic-based measurements. It has been reported that epidemiological studies that rely on single-session measurements over-diagnose hypertension by 20-25%.18 If we discount this proportion, 19% adults in the urban and 7.5% in the rural areas shall be eligible for hypertension therapies. Translating these proportions into numbers reveals a massive burden of this disease in India. According to 2001 census there are 600 million adults in India of whom 420 million are in rural and 180 million in urban areas and the absolute number of hypertensives in India shall be 31.5 million rural and 34 million urban subjects, a total of 65.5 million. An Indian epidemiological study reported that 70% of these would be Stage I hypertension (systolic BP 140-159 and/or diastolic BP 90-99 mm Hg).26 The stage I hypertension (45.5 million subjects) can be managed initially by lifestyle measures. However, recent reports from the Seven Countries Study27 and Framingham Study28 show that borderline hypertension (systolic BP 130-139 and/or diastolic BP 85-89 mm Hg) and stage I hypertension carries a significant cardiovascular risk and there is need to reduce this blood pressure. Pharmacological therapies in this class of individuals need more studies although TOMHS demonstrated that it is helpful in reducing cardiovascular end-points. 24 For Stage 2 and 3 hypertension multiple studies recommend pharmacological therapy and, therefore,20 million persons in India belonging to this class require regular anti-hypertensive medications. This carries a huge economic burden on already over-stressed Indian economy. Studies that examine cost-effective approaches to optimally control blood pressure among Indians are needed. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| REFERENCES |
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| EDITOR IN CHIEF |
| Dr.
Rajeev Gupta (MD PhD FACC) |
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| HON. EDITOR |
| Dr.
Soneil Guptha (MD FACC FESC) |
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