Cohort studies around the world: methodologies, research questions and integration to address the emerging global epidemic of chronic diseases

With ageing populations, increased economic prosperity and the ensuing lifestyle changes, there has been a dramatic increase in the burden of chronic non-communicable diseases in countries of the developing world. The distribution of risk factors for chronic diseases among populations in developing countries has traditionally been very different from that in their Western counterparts, thus resulting in considerable variation in disease distribution in these settings. However, with the increase in globalization along with rapid advancements in technology, many developing countries are now faced with the challenge of a dual disease burden, battling existing communicable infectious diseases as well as the emerging epidemic of non-communicable chronic diseases. This paper highlights the need for multiple cohort studies on chronic diseases around the world, and explores some of the challenges in establishing and maintaining these studies in resource-constrained settings.     

Introduction. Symposium: Obesity in developing countries: biological and ecological factors

Over the past decade there has been an increasing concern about the impact of chronic, noncommunicable diseases on the health of developing world populations. Traditionally, major causes of illness and death in developing countries have been linked to infectious diseases and undernutrition, and these are still major public health problems in several regions of the world. But recent projections indicate that in 20 y noncommunicable diseases will account for over 60% of the disease burden and mortality in the developing world. Obesity is recognized as an underlying risk factor for many of these chronic conditions. As in developed societies, the risk for obesity in developing countries is also strongly influenced by diet and lifestyle, which are changing dramatically as a result of the economic and nutrition transition. This symposium discusses key aspects of the phenomenon of obesity in the developing world and provides some specific examples from countries facing increasing prevalence of that condition.     

Nutritional transition and non-communicable diet-related chronic diseases in developing countries

It is increasingly recognized that developing countries are undergoing an epidemiologic transition similar to that which occurred in industrialized countries in previous centuries. While infectious diseases are still the main cause of morbidity and mortality, there is a marked increase in chronic non-communicable diseases, particularly in the most advanced developing countries, and these diseases are expected to take the lead in a decade or two. Most of these diseases, above all coronary heart diseases, stroke and diabetes, are related to diet and lifestyles, for example tobacco and alcohol consumption. As a matter of fact, these societies are also facing a growing epidemic of overweight and obesity, due to the frequent energetic imbalance between energy-dense food consumption and reduced daily physical expenditure. This health transition, favoured by demographic changes towards aging populations, is occurring at an increased pace in urban societies widely exposed to the modernization of lifestyle, sedentary occupation, and to lipid- and sugar-rich food, often poor in fibre and micronutrients. Increased world access to cheaper vegetable oil is thought to have triggered off this accelerated and generalized trend, though animal food, rich in saturated fat, and imported or locally-made industrialized food also play a role. While increased national and household incomes facilitate the initial change, as the transition advances poor people progressively become the main victims, as has been observed in the more advanced developing countries. Metabolic imprinting due to intra-uterine and infant malnutrition, which are still common in these societies, is also thought to play a significant role in the increase in the expression of insulin resistance, obesity and chronic diseases when these children are exposed to abundant food and modern lifestyle, later in life. Treatment and secondary prevention of nutrition-related chronic diseases and associated disabilities have an ever rising cost in industrialized countries, which is far beyond the means of the still fragile economies of developing countries. This double burden of infectious diseases and undernutrition that still exist, and of non-communicable diseases and overnutrition represents a threat to the frequently unprepared health care services in developing countries. There is a clear need to focus health policies on the prevention of chronic diseases through primary health care services, the use of mass media for communication and education about healthy nutrition and lifestyle, and the adaptation of public policies. Nutritionists must also adapt to this changing nutritional situation which may result in apparently contradictory nutritional status findings within societies if not even within households.     

Contrasting socioeconomic profiles related to healthier lifestyles in China and the United States

Health disparity by socioeconomic status has recently become an important public health concern. Socioeconomic status may affect health status through several pathways including lifestyle choices. The authors tested the link between socioeconomic status and lifestyle in China (in 1993) and in the United States (in 1994-1996), countries with high contrasts in development, to understand health discrepancy issues cross-nationally. Healthfulness of lifestyle was measured using the Lifestyle Index, a summary score that integrates four key lifestyle factors: diet, physical activity, smoking, and alcohol consumption. Income and education were used as indicators of socioeconomic status. In China, as socioeconomic status improved, lifestyle was less healthy (relative odds for the highest socioeconomic status group = 0.19, 95% confidence interval: 0.10, 0.35). Conversely, in the United States, higher socioeconomic status was related to a healthier lifestyle (relative odds for the highest socioeconomic status group = 3.81, 95% confidence interval: 2.94, 4.94). The contrasting relation between socioeconomic status and lifestyle depicts different phases of the lifestyle transition (changes in lifestyles accompanying economic development). The differences may in part explain why nutrition-related noncommunicable diseases are more prevalent in the developing world among people with a high socioeconomic status, whereas often the opposite is found in developed societies. Public health programs may benefit by advising each socioeconomic status group separately, while considering the country's level of development.     

Epidemiological and nutrition transition in developing countries: impact on human health and development

Whereas common infectious and parasitic diseases such as malaria and the HIV/AIDS pandemic remain major unresolved health problems in many developing countries, emerging non-communicable diseases relating to diet and lifestyle have been increasing over the last two decades, thus creating a double burden of disease and impacting negatively on already over-stretched health services in these countries. Prevalence rates for type 2 diabetes mellitus and CVD in sub-Saharan Africa have seen a 10-fold increase in the last 20 years. In the Arab Gulf current prevalence rates are between 25 and 35% for the adult population, whilst evidence of the metabolic syndrome is emerging in children and adolescents. The present review focuses on the concept of the epidemiological and nutritional transition. It looks at historical trends in socio-economic status and lifestyle and trends in nutrition-related non-communicable diseases over the last two decades, particularly in developing countries with rising income levels, as well as the other extreme of poverty, chronic hunger and coping strategies and metabolic adaptations in fetal life that predispose to non-communicable disease risk in later life. The role of preventable environmental risk factors for obesity and the metabolic syndrome in developing countries is emphasized and also these challenges are related to meeting the millennium development goals. The possible implications of these changing trends for human and economic development in poorly-resourced healthcare settings and the implications for nutrition training are also discussed.     

The global impact of noncommunicable diseases: estimates and projections

With the aging of populations in developing countries there is both a demographic and an epidemiological transition which affects the impact of chronic degenerative diseases on the health status of the populations. Demographic transition takes place in countries where there are effective programmes of disease control which allow for survival during the early years of childhood and adolescence. This results in an increase in life expectancy which places larger proportions of the population in the age range (60 years and older) in which chronic degenerative diseases become the major determinants of health status. Epidemiological transition in diseases may also be brought about by shifts in social and economic patterns which favour detrimental changes in risk factors for the chronic degenerative diseases. Such changes may include health-related behaviour which augments dietary consumption of fats and alcohol, increases obesity, increases smoking and decreases physical activity. Such changes in risk-factor levels increase the prevalence of chronic degenerative diseases which manifest themselves at later ages, and for which early preventive actions could be cost-effective. In order to illustrate the impact of both demographic and risk-factor effects, analyses are made of the impact of increases in life expectancy on cause-specific mortality in both developing and developed countries. It is shown that there is great similarity in the effect of major noncommunicable diseases on the life expectancy of adults in both developed and developing countries. The major differences are seen to be in the proportions of deaths expected from such diseases as cancer, diabetes, heart disease, stroke and cirrhosis; but not in the distribution of age at death which is the better measure of disease impact. Demographic analyses, computing indirect estimates of mortality, also demonstrate that there are currently more chronic disease deaths in developing than developed countries and that as expectation of life increases in developing countries the global chronic disease burden will be greatly concentrated in the developing countries. Analyses of risk-factor reduction by feasible intervention strategies, e.g. smoking cessation campaigns, treatment of high blood pressure, using relationships between risk factors and diseases established in longitudinal studies carried out in developed countries, point out that the effect of risk-factor control in long-living populations can be hidden by the dependency of risk factors and various related causes of death, e.g. smoking has an impact on lung cancer, ischaemic heart disease and emphysema, but at different ages.(ABSTRACT TRUNCATED AT 400 WORDS)     

山东省6县（区）部分人群预防SARS行为调查分析

目的了解山东省不同地域居民SARS流行期生活行为及流行前后行为变化情况。方法选择城市和乡镇社区对于SARS传播和控制意义较重要的具有代表性的7个人群进行入户式现场调查。结果人们从个人卫生、公共卫生、提高身体素质、减少接触机会、维护生态平衡等多个方面约束或改进了个人行为。92.0%的被调查者认为非典流行促使自己改进了生活习惯。结论山东省人群非典期间采取预防行为的比率很高,为今后SARS、禽流感及其他呼吸道传染病的预防奠定了良好的基础。     

Obesity and diabetes in vulnerable populations: reflection on proximal and distal causes

Around the world obesity and diabetes are climbing to epidemic proportion, even in countries previously characterized by scarcity. Likewise, people from low-income and minority communities, as well as immigrants from the developing world, increasingly visit physicians in North America with obesity, metabolic syndrome, or diabetes. Explanations limited to lifestyle factors such as diet and exercise are inadequate to explain the universality of what can be called a syndemic, a complex and widespread phenomenon in population health produced by multiple reinforcing conditions. Underlying the problem are complex factors-genetic, physiological, psychological, familial, social, economic, and political-coalescing to overdetermine these conditions. These interacting factors include events occurring during fetal life, maternal physiology and life context, the thrifty genotype, the nutritional transition, health impact of urbanization and immigration, social attributions and cultural perceptions of increased weight, and changes in food costs and availability resulting from globalization. Better appreciation of the complexity of causation underlying the worldwide epidemic of obesity and diabetes can refocus the work of clinicians and researchers to work at multiple levels to address prevention and treatment for these conditions among vulnerable populations.     

Health sector reform in South Asia: new challenges and constraints

In early 1990s, Jamison, Mosley and others concluded that a profound demographic and consequent epidemiological transition is taking place in developing countries. According to this classical model, by the year 2015, infectious diseases will account for only about 20% of deaths in developing countries as chronic diseases become more pronounced. These impending demographic and epidemiological transitions were to dominate the health sector reform agenda in developing countries. Following an analysis of fertility, mortality and other demographic and epidemiological data from South Asian and other developing countries, the paper argues that the classical model is in need of re-evaluation. A number of new 'challenges' have complicated the classical interplay of demographic and epidemiological factors. These new challenges include continuing population growth in some countries, rapid unplanned urbanization, the HIV/AIDS pandemic in Sub-Saharan Africa (and its impending threat in South Asia), and globalization and increasing marginalisation of developing countries. While the traditional lack of investment in human development makes the developing countries more vulnerable to the vicissitudes of globalization, increasing economic weakness of their governments forces them to retreat further from the social sector. Pockets of poverty and deprivation, therefore, persist giving rise to three simultaneous burdens for South Asia and much of the rest of the developing world: continuing communicable diseases, increasing burden of chronic diseases, and increasing demand for both primary and tertiary levels of health care services. While these complex factors, on the one hand, underscore the need for health sector reform, on the other, they make the task much more difficult and challenging. The paper emphasizes the need to revisit the classical model of demographic and epidemiological transition. It is argued that the health sector in developing countries must be aware of and effectively address these 'new challenges'. Although it has included data from many developing countries, the focus is primarily on South Asia.     

Reducing the growing burden of cardiovascular disease in the developing world

Cardiovascular disease (CVD) has become the number-one cause of death in the developing world. This epidemic has the potential to place a large social and economic burden on developing countries, where CVD tends to strike those in their prime working years. Since resources for managing CVD are limited, it is important that interventions be guided by cost-effectiveness results for low- and middle-income countries. Despite the burden, cost-effective strategies exist at the population and individual levels for reducing CVD. Integral to all personal intervention strategies is an adequate assessment of the underlying risk of disease.     

An overview of cardiovascular risk factor burden in sub-Saharan African countries: a socio-cultural perspective

Background  

Sub-Saharan African (SSA) countries are currently experiencing one of the most rapid epidemiological transitions characterized by increasing urbanization and changing lifestyle factors. This has resulted in an increase in the incidence of non-communicable diseases, especially cardiovascular disease (CVD). This double burden of communicable and chronic non-communicable diseases has long-term public health impact as it undermines healthcare systems.     

Association among 5-year changes in weight, physical activity, and cardiovascular disease risk factors in Mexican Americans

Recent changes in lifestyle have led to a global epidemic of obesity. To determine the associations of these changes with cardiovascular disease (CVD) risk, the authors correlated changes in CVD risk factors with changes in weight and physical activity in a population-based sample of 539 Mexican Americans in the San Antonio Heart Study in 1992-1999 who were examined twice approximately 5 years apart. Average weight change during that interval was 2.7 kg. While change in physical activity (expressed as percent change) was associated modestly only with change in low density lipoprotein cholesterol median diameter (p = 0.017), weight change was strongly and positively associated with unfavorable changes in lipid and lipoprotein traits, insulin levels, and blood pressure, explaining 2-10% of the variation in the risk factor changes during the interval. The unfavorable associations with weight gain tended to be more pronounced in lean compared with obese individuals and in men compared with women. However, the associations were significant for most CVD risk factors in all groups. In Mexican Americans, a population at high risk for obesity, weight change was positively correlated with metabolic variables associated with risk of CVD. Therefore, increasing adiposity in this population may tend to slow, or even reverse, the decline in CVD morbidity and mortality.     

Globalization, diet, and health: an example from Tonga

The increased flow of goods, people, and ideas associated with globalization have contributed to an increase in noncommunicable diseases in much of the world. One response has been to encourage lifestyle changes with educational programmes, thus controlling the lifestyle-related disease. Key assumptions with this approach are that people's food preferences are linked to their consumption patterns, and that consumption patterns can be transformed through educational initiatives. To investigate these assumptions, and policies that derive from it, we undertook a broad-based survey of food-related issues in the Kingdom of Tonga using a questionnaire. Data on the relationships between food preferences, perception of nutritional value, and frequency of consumption were gathered for both traditional and imported foods. The results show that the consumption of health-compromising imported foods was unrelated either to food preferences or to perceptions of nutritional value, and suggests that diet-related diseases may not be amenable to interventions based on education campaigns. Given recent initiatives towards trade liberalization and the creation of the World Trade Organization, tariffs or import bans may not serve as alternative measures to control consumption. This presents significant challenges to health policy-makers serving economically marginal populations and suggests that some population health concerns cannot be adequately addressed without awareness of the effects of global trade.     

Ketogenic Diet,Physical Activity,and Hypertension—A Narrative Review

Several studies link cardiovascular diseases (CVD) with unhealthy lifestyles (unhealthy dietary habits, alcohol consumption, smoking, and low levels of physical activity). Therefore, the strong need for CVD prevention may be pursued through an improved control of CVD risk factors (impaired lipid and glycemic profiles, high blood pressure, and obesity), which is achievable through an overall intervention aimed to favor a healthy lifestyle. Focusing on diet, different recommendations emphasize the need to increase or avoid consumption of entire classes of food, with only partly known and only partly foreseeable consequences on the overall level of health. In recent years, the ketogenic diet (KD) has been proposed to be an effective lifestyle intervention for metabolic syndrome, and although the beneficial effects on weight loss and glucose metabolism seems to be well established, the effects of a prolonged KD on the ability to perform different types of exercise and the influence of KD on blood pressure (BP) levels, both in normotensives and in hypertensives, are not so well understood. The objective of this review is to analyze, on the basis of current evidence, the relationship between KD, regular physical activity, and BP.     

Economic change and sex-specific cardiovascular mortality in Britain 1955–1976

Analyses directed toward recent declines in cardiovascular disease mortality rates have typically focused on alterations in important physiological and behavioral risk factors resulting from lifestyle changes and medical advances.In this study, a multivariate model of the impact of more fundamental changes in the socioeconomic and bio-physical environments has been developed and applied to cardiovascular disease mortality rates, by sex, in England and Wales and Scotland during 1955–1976. The predictive model includes factors associated with (1) long-term growth in the economy, (2) deleterious behavioral risk factors loosely associated with economic growth—especially cigarette consumption per capita, (3) economic instability—especially recession as indicated by factors related to unemployment, income loss, and recessional declines in average weekly hours worked in manufacturing industries, (4) health care, and (5) physical environmental disturbances—especially very cold temperatures.This model proves to be an excellent instrument for the statistical explanation of trends and fluctuations in CVD mortality rates for both sexes and both regions in Britain in the post-War period. In general, the overall exponential rate of economic growth is found to be the most powerful factor in the long-term decline in CVD mortality rates. Similarly, disturbances to the national and regional economic situations—especially recessions—have regularly been associated with elevated death rates for all populations observed. Cigarette and unusually high spirits consumption, as well as particularly cold winter temperatures, have also had important deleterious effects on CVD mortality. The proportion of government expenditures devoted to health care is associated with a reduction in CVD mortality in England and Wales.     

Globalization, Socioeconomic Restructuring, and Community Health

New trends in global public health have social, economic, and political underpinnings that can be found in three 20th century revolutions: globalization, a new epidemiological transition, and an historical shift in patterns of production and consumption throughout the world. Globalization is more than the internationalization of commerce and manufacture; it represents a new development paradigm that creates new links among corporations, international organizations, governments, communities, and families. Social and economic restructuring is reflected in the emerging health profile in underdeveloped countries, including those in Latin America. This emerging profile defies simple categorization, however; while the prevalence of cardiovascular disease and cancer has increased, the traditional diseases (infectious and respiratory disease) are still the leading cause of death. At the same time, industrialized countries are experiencing the re-emergence of those same traditional diseases. These apparent anomalies can be understood by examining class structures within and among countries and by linking health outcomes at the local level to new patterns of production and consumption in the global system.     

Economic burden of expected epidemiological changes in diseases related to tobacco, Mexico

OBJECTIVE: To determine health care costs and economic burden of epidemiological changes in diseases related to tobacco consumption. METHODS: A time-series analysis in Mexico (1994-2005) was carried out on seven health interventions: chronic obstructive pulmonary diseases, lung cancer with and without surgical intervention, asthma in smokers and non-smokers, full treatment course with nicotine gum, and full treatment course with nicotine patch. According with Box-Jenkins methodology, probabilistic models were developed to forecast the expected changes in the epidemiologic profile and the expected changes in health care services required for selected interventions. Health care costs were estimated following the instrumentation methods and validated with consensus technique. RESULTS: A comparison of the economic impact in 2006 vs. 2008 showed 20-90% increase in expected cases depending on the disease (p<0.05), and 25-93% increase in financial requirements (p<0.01). The study data suggest that changes in the demand for health services for patients with respiratory diseases related to tobacco consumption will continue showing an increasing trend. CONCLUSIONS: In economic terms, the growing number of cases expected during the study period indicates a process of internal competition and adds an element of intrinsic competition in the management of preventive and curative interventions. The study results support the assumption that if preventive programs remain unchanged, the increasing demands for curative health care may cause great financial and management challenges to the health care system of middle-income countries like Mexico.     

Dietary Phosphorus Excess: A Risk Factor in Chronic Bone,Kidney, and Cardiovascular Disease?

There is growing evidence in the nephrology literature supporting the deleterious health effect of excess dietary phosphorus intake. This issue has largely escaped the attention of nutrition experts until this symposium, which raised the question of whether the same health concerns should be extended to the general population. The potential hazard of a high phosphorus intake in the healthy population is illustrated by findings from acute and epidemiologic studies. Acute studies in healthy young adults demonstrate that phosphorus intakes in excess of nutrient needs may significantly disrupt the hormonal regulation of phosphorus contributing to disordered mineral metabolism, vascular calcification, bone loss, and impaired kidney function. One of the hormonal factors acutely affected by dietary phosphorus loading is fibroblast growth factor-23, which may be a key factor responsible for many of the cardiovascular disease (CVD) complications of high phosphorus intake. Increasingly, large epidemiological studies suggest that mild elevations of serum phosphorus within the normal range are associated with CVD risk in healthy populations. Few population studies link high dietary phosphorus intake to mild changes in serum phosphorus due to study design issues specific to phosphorus and inaccurate nutrient composition databases. The increasing phosphorus intake due to the use of phosphorus-containing ingredients in processed food and the growing consumption of processed convenience and fast foods is an important factor that needs to be emphasized.     

Metabolic-Associated Fatty Liver Disease (MAFLD), Diabetes,and Cardiovascular Disease: Associations with Fructose Metabolism and Gut Microbiota

Non-alcoholic fatty liver disease (NAFLD) is an increasingly common condition associated with type 2 diabetes (T2DM) and cardiovascular disease (CVD). Since systemic metabolic dysfunction underlies NAFLD, the current nomenclature has been revised, and the term metabolic-associated fatty liver disease (MAFLD) has been proposed. The new definition emphasizes the bidirectional relationships and increases awareness in looking for fatty liver disease among patients with T2DM and CVD or its risk factors, as well as looking for these diseases among patients with NAFLD. The most recommended treatment method of NAFLD is lifestyle changes, including dietary fructose limitation, although other treatment methods of NAFLD have recently emerged and are being studied. Given the focus on the liver–gut axis targeting, bacteria may also be a future aim of NAFLD treatment given the microbiome signatures discriminating healthy individuals from those with NAFLD. In this review article, we will provide an overview of the associations of fructose consumption, gut microbiota, diabetes, and CVD in patients with NAFLD.