Changing trends in the prevalence of coronary heart disease.

Coronary heart disease (CHD) is the leading cause of death and disability and has major impact on developing and developed nations. CHD is the most common serious chronic illness that evolves over years but remains undiagnosed until it presents with life-threatening situations. It is the most common preventable non-communicable disease that is frequently associated with high-fat and energy-rich diet, smoking and sedentary lifestyles and is a consequence of rapid demographic transition and economic liberalization. According to the National Commission on Macroeconomics and Health the estimated number of CHD patients in India increased from 29.8 millions in 2004 to 61.5 millions in 2015 and the estimated mortality from CHD staggered from 1.3 millions in 2000 to 2.946 millions in 2015.1, 2 The coronary heart disease prevalence rates are extremely variable in different parts of the world and CHD trends are not consistent even among countries within the same geographic region. CHD drew public attention when it reached epidemic proportions in USA in early part of twentieth century and in Europe in mid twentieth century and as a result various studies like Framingham Heart Study in 1948 (FHS), seven countries study in 1958, Monica project in 1979, and similar epidemiological studies were conducted to assess the reasons for these increasing trends in CHD prevalence. Much of the current knowledge on the relation ship between diet, lifestyle and CHD was drawn from the seven countries study. The FHS was instrumental in identifying many of the factors associated with increased risk of CHD. The Monica project was developed by WHO to measure the incidence and determinants of fatal and non-fatal CHD in various populations. The increased awareness created by these studies has provided the impetus for public health initiatives against these major risk factors and the concept of preventive cardiology and as a result 2–3% annual decline in CHD prevalence rates were observed in these developed countries. The Inter Heart Study in 1999 was a response to the call given by Institute of Medicine for global data on CHD risk factors and this case control study demonstrated that abnormal lipids, smoking, hypertension, diabetes, abdominal obesity, psychosocial factors, consumption of fruits, vegetables, and alcohol, and regular physical activity account for most of the risk of myocardial infarction worldwide in both sexes and at all ages in all regions.

CHD prevalence studies in India date back to 1960 and were based on autopsy reports and insurance statistics. CHD prevalence rates in these studies varied between 0.49% and 0.63% and the prevalence rates were 6.5 times higher in males compared to females. The first Indian study involving Minnesota codes was in 1974 by Dewan which reported a CHD prevalence of 2.28% in men and 1.73% in women in rural Maharashtra. In 1987–88 Chada et al. reported 2.71% CHD prevalence rate in rural Haryana. ICMR task force study conducted in 1991–94 reported CHD prevalence rates of 11% and 10% in urban Delhi among men and women respectively. At the same time the rural areas in Haryana had a lower prevalence of CHD (5.6% and 6.4%). Studies conducted by Gupta et al. in Jaipur in 1992–95 and 2001 revealed CHD prevalence rates of (5.96% and 6.18%) and (10.5% and 10.1%) among men and women. Ramachandran et al. reported 4% CHD prevalence rate in Chennai during 1994 while Mohan et al. reported higher prevalence rate (11%) during 1996–97. Kutty et al. conducted studies in rural Kerala and reported CHD prevalence rates of 7.4% in subjects aged above 25 years. In 1995 Beegom et al. reported CHD prevalence rate of 13.9% in urban areas of Trivandrum. Oommen et al. in their study (published in this issue of IHJ) examined the trends in the prevalence of CHD in the same rural and urban pockets of Vellore district in Tamil Nadu over a period of two decades and observed a twofold rise in the prevalence of CHD among women in rural areas and a threefold rise in urban areas with a modest rise among males. The authors also noticed a rising trend in coronary risk factors with a shift in the age of onset of CHD towards younger age groups. One significant observation in this study was CHD prevalence rates are more or less same in men over the past 20 years in spite of rising trends in risk factors where as there is a sharp rise in the prevalence among women in both urban and rural communities indicating a reversal of trend in the incidence of CHD with respect to gender. Even though sedentary life styles, rising obesity rates and increasing smoking rates in women contribute to this phenomenon, this observation needs further validation. In this study more number of subjects was labelled as CHD based on symptoms alone and majority of those subjects who had ECG changes were asymptomatic. As rightly pointed out by the authors the predictive validity of Rose questionnaire in India has to be validated in the absence of ECG changes. The authors should be lauded for conducting the resurvey in the same region as few such resurveys are available in Indian literature which monitored the CHD prevalence trends over a period of two decades. Irrespective of the nature of studies; all studies conducted in the last two decades indicate a two to four fold rise in the prevalence of CHD.

Rising CHD trends in India can be attributed partly to increasing life expectancy of the population and consequent increase in biological risk factors. However, while CHD is now predominantly a disease of old age in industrialized countries premature CHD is more common in developing countries such as India as shown in the present study with higher prevalence rates even among premenopausal women. Rapid urbanization had its impact on CHD incidence and it is well documented that city living has been associated with higher rates of physical inactivity related obesity and greater mental stress. Smoking is a major risk factor for CHD and Tobacco – consumption has gone up by 2.8% in the previous three decades and 1.7% in the last decade. Cigarette manufacturers have concentrated on developing countries to create newer markets as a response to their dwindling sales in industrialized nations. Tobacco companies also got benefited from the liberalization of trade regimes. Together smoked and smokeless tobacco consumption in India exceeds 50% in men and 20% in women as per recent WHO estimates. Epidemiologic transition had its toll on CHD by increasing the consumption of energy dense diets rich in unhealthy fats, oils, sodium and sugars. The gradual disappearance of longstanding practice of faith based vegetarianism is an example of this epidemiological transition. Alarming rise in the prevalence of diabetes and chronic kidney disease in the last few decades had significant effect on CHD prevalence. Hypertension prevalence rates are around 30% in India and only one third are optimally treated. Rising trends in obesity as a result of increased consumption of food and fuel have fuelled the growth of CHD as shown in the present article. Under nutrition is reported among one third of children in this country and recent evidence suggests association between childhood under nutrition and adult onset CHD. Physical activity levels, particularly leisure time physical activity levels are low in India and evidence from Inter Heart Study reveals physical inactivity is a contributor for CHD. Dyslipidemia is seen in more than one fourth of Indian population. Low HDL and high levels of triglycerides are common among Indians and both these confer higher risk for CHD. Elevated Apo B/Apo A-1 ratio was found to be an important risk factor responsible for CHD in Indians. Even though vegetarianism is common in India fruit and vegetable consumption rates were low compared to rest of the world.6, 7 The present trend towards an escalation of CHD in India reflects rapidly changing patterns of social, economic and cultural behaviour, associated with urbanization and international trade in commodities such as food or tobacco which was seen in more developed countries in mid twentieth century. In general it is observed that communicable diseases predominate in countries at an early stage of epidemiological transition followed later by non-communicable diseases.

Two sets of studies explained the changing trends in CHD; the first set of studies (for example Monica Study) examined the causes for increased incidence and mortality rates and the second set of studies (ARIC Study) examined declining trends. Relatively few major behavioural and biological risk factors accounted for CHD incidence around the world. The key contributors to the rise in CHD across countries at all stages of development included tobacco use, abnormal blood lipids, unhealthy dietary changes and physical inactivity. The key contributors for decline in CHD in some countries include reduced tobacco use, a shift towards healthful diets, population wide preventive measures and quality treatment interventions. The North Karelia project in Finland is an important example of a comprehensive public health program that changed the CVD producing habits of the population (Table 1).

Table 1

Trends in CHD mortality rates for 100,000 populations in different nations in the years 2000 and 2012.

Country	2000			2012
	Male	Female	Total	Male	Female	Total
Australia	115.4	60.6	85.3	93.9	48.7	68.6
Brazil	125.7	78.3	100.2	97.6	54	73.7
Canada	121.5	59.3	86.7	97	80.3	88.2↑
China	58	63.4	53	105.7	98.9	102.6↑
Denmark	120.9	61.8	87.6	54.2	26	39
Egypt	225.9	159.6	189.1	236.1	165.3	197.2↑
Nepal	129.6	101.8	115.3	122.5	96.5	109.4
New Zealand	139.7	70.9	101.6	70.5	37.1	52.9
Norway	129	61.1	90.4	62.3	30.7	45.3
Pakistan	97.5	117.4	106.6	118	124.5	121↑
Russian Federation	514.7	247.9	349.5	473.1	218.7	312.9
Singapore	132.2	86	107.6	83.8	42.7	61.8
Sri Lanka	240.8	140.4	188.9	211.7	115.2	159.4
Sweden	133.4	63.4	94.3	78.5	39.9	57.3
Turkey	267.1	152.2	200.4	197.7	113.4	148.7
United Kingdom	151.1	71.9	107	75.4	32.5	52
United States	152.5	83.9	114	91	46	66.3
India	372.8	302	337.6	348.9	264.6	306.3

Even though there is considerable knowledge on aetiology and modifiable risk factors for CHD, transforming this body of evidence in to large scale feasible efforts to the specific needs of a country is difficult. Determining the nature and extent of the CHD risk factors in the local populations is the first step for a successful prevention strategy. Effective control of CHD at the population level involves educating the population on the necessary dietary and behavioural changes for good cardiac health, changing the public policy to create heart healthy environments, encouraging heart healthy partner ships between governments and civil societies and persuading industries to reduce the sale of tobacco products and unhealthy foods. As accumulation of cardiovascular risk begins early in life, a life course approach is needed to promote cardiovascular health. The health professionals should not get biased towards a technological solution to this problem as opposed to prevention as social determinants play as much role as biological and genetic factors in the causation of CHD.