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Available online at www.sciencedirect.com
ScienceDirect www.onlinepcd.com
Descriptive Epidemiology of Cardiovascular Risk Factors and Diabetes in Sub-Saharan Africa George A. Mensah⁎ Office of the Director, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD
A R T I C LE I N FO
AB S T R A C T
Keywords:
Reliable data on risk factor levels, exposure history, and population distribution can help
Cardiovascular diseases
inform policies and programs for disease prevention and control. With rare exception
Sub-Saharan Africa
however, ideal local data on major risk factors and causes of death and disease burden have
Cardiovascular risk factors
been scarce in sub-Saharan Africa (SSA). Basic community surveys in some countries and recent systematic analysis of disease burden attributable to 67 risk factors and risk factor clusters in 21 regions of the world provide an opportunity to examine and relate diabetes and cardiovascular risk factors to mortality and burden in SSA. Rising body mass index, especially in women in Southern Africa; and rising systolic blood pressure in East Africa for both sexes, and in West Africa for women are the major cardiometabolic risk factors. Harmful use of alcohol, especially in Southern SSA, tobacco use, and physical inactivity are also important. Improving vital registration and risk factor surveillance remain major challenges. Published by Elsevier Inc.
The landmark Framingham Heart Study introduced the concept that current or past exposure to specific factors increases the risk of future cardiovascular disease.1 These “factors of risk” are now well described for coronary heart disease, stroke, other cardiovascular diseases (CVD), and diabetes and are the same in sub-Saharan Africa (SSA) as they are in other parts of the world. These risk factors include high blood pressure (BP); tobacco use, including exposure to second-hand smoke; harmful use of alcohol; high total blood cholesterol; high fasting plasma glucose (FPG); high body mass index (BMI); high intake of dietary sodium; low dietary intake of fruits and vegetables; low physical activity; and household and ambient air pollution.
Statement of Conflict of Interest: see page: 248. Disclaimer: The views expressed in this article do not necessarily represent the views of the National Heart, Lung, and Blood Institute, National Institutes of Health, Department of Health and Human Services or any other government entity. ⁎ Address reprint requests to George A. Mensah, NIH/NHLBI/IOD, 31 Center Drive MSC 2486, Bethesda, MD 20892-2490. E-mail address: [email protected]. 0033-0620/$ – see front matter. Published by Elsevier Inc. http://dx.doi.org/10.1016/j.pcad.2013.10.014
Together, known risk factors explain the majority of the population burden of total CVD. For example, Yusuf et al. showed that nine potentially modifiable risk factors collectively accounted for 90% and 94% of the population attributable risk for first-time acute myocardial infarction (AMI) in men and women, respectively in 52 countries.2 In the African population of the INTERHEART Study, five risk factors (smoking history, diabetes history, hypertension history, abdominal obesity, and ratio of apolipoprotein B to apolipoprotein A-1) contributed a similar population attributable risk of nearly 90% for AMI.3 In general, the magnitude and duration of exposure to these risk factors determine the level of risk of future disease-related outcomes. Thus, accurate and reliable information on risk factor levels and their population distribution can help inform policies and programs for prevention, treatment, and control. With rare exception however, ideal and reliably enumerated epidemiological data on these major risk factors have not been readily available in SSA. Recent completion of the systematic analysis of the burden of disease and injury attributable to 67 risk factors and risk factor clusters in 21 regions of the world including
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Abbreviations and Acronyms
four regions in SSA, and other global burBMI = body mass index den of disease BP = blood pressure assessments4–12 provide a unique opporCHD = Coronary heart disease tunity to examine and CVD = Cardiovascular disease relate these risk factors to mortality and DALY = disability-adjusted life disease burden in SSA year using comparable FPG = fasting plasma glucose methodology. Progress made in the GBD = Global Burden of Diseases World Health OrganiSSA = sub-Saharan Africa zation’s STEPS chronic disease risk factor STEPS = Stepwise approach to surveillance in this rechronic non-communicable disgion is also reviewed ease surveillance together with previTC = Total cholesterol ously published data from specific risk facWHO = World Health tor studies in SSA. Organization Although the focus of this article is CVD and diabetes, it must be emphasized that in most of SSA, the leading threats to health continue to be those associated with poverty and maternal and child mortality as shown in Fig 1.4 However, the ongoing health transitions together with adverse impact of globalization and urbanization13–17 in SSA make it necessary to promote the development of the capacity to monitor the magnitude and trends in diabetes18–20 and CVD4,21 risk factors in order to better inform programs and policies for the prevention and control of diabetes and CVD in SSA.
CVD risk factors in sub-Saharan Africa – the background A high prevalence of adverse CHD risk factors in the nineteenth and early twentieth centuries in SSA seems very unlikely given the rarity of CHD in the published historical data from western, eastern, central, and southern Africa from that period.22 For example, extensive review of the Annual Medical and Sanitary Reports sent regularly to the Colonial Secretary in London by the Nigerian and Gold Coast governments showed that coronary heart disease was distinctly rare from 1898 to 1960.23–25 Since the turn of the twenty-first century however, the weight of the published data suggests that diabetes and CVD risk factors are increasing in prevalence in SSA in men and women, and in children and adults. For example, in a birth cohort study of CVD risk factors in 5-yearold children living in an urban environment in South Africa in 1990, Steyn et al.26 showed that overall, 64% of the children were already exposed to environmental tobacco smoke with the highest exposures observed in colored children; among these colored children, 42% lived in homes with two or more smokers.26 Significant ethnic differences observed included significantly higher blood pressure in black children in whom diastolic blood pressure levels were also the highest.
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A similarly high CVD risk factor prevalence was observed in a random population-based sample of 976 people aged 15 years and older in a peri-urban working-class community in South Africa.27 Hypertension prevalence was 22% in men and 16% in women; 62% of men and 44% of women smoked cigarettes; hypercholesterolemia was present in nearly half of the population (47% of men, and 46% of women); while diabetes was prevalent in 6% of men and 5% of women.27 In the predominantly Black African community of Soweto, Tibarzawa et al.28 showed that nearly 78% of subjects had at least one major CVD risk factor. The most prevalent CVD and diabetes risk factor in this middle-aged adult population was obesity (43%) with nearly a 2-fold greater prevalence in women than in men.28 Additionally, 33% of subjects had high systolic or diastolic blood pressures, and 13% had elevated (non-fasting) total blood cholesterol level. Importantly, overweight subjects were three times more likely to have concurrent hypercholesterolemia.28 This relatively high burden of CVD risk factors and diabetes in population sub-groups in South Africa should not be assumed to be representative of the rest of SSA because of the relatively more advanced stage of epidemiologic, socioeconomic, and nutritional transition in South Africa compared to other parts of SSA.29 Nevertheless, the trend of increasing prevalence in CVD risk factors in most countries where studies have been performed is unmistakable.30 An important limitation in making international and inter-regional comparisons is the wide heterogeneity of studies and differences in sample sizes, sampling methodologies, diagnostic approaches and criteria; different age distributions; and different study settings with varying representation of rural and urban populations. For example, in the recent systematic review of the evidence on the prevalence and pathogenesis of type 2 diabetes published in Africa over the past decade, Kengne et al.31 identified 13 community-based studies from nine SSA countries and Tunisia. They found a ten-fold difference in reported diabetes prevalence ranging from 2.8% in rural Angola to 28.2% in an urban population setting in South Africa.31 Similarly, the reported prevalence of obesity in 20 studies they identified ranged from 5% in rural Uganda to 30% in urban Nigeria.31 Their overall assessment of the quality of these data was that, in general, these data do not provide accurate estimates of the magnitude of the conditions studied. It is in this regard that the WHO stepwise approach to chronic non-communicable disease surveillance (STEPS) and other studies that use comparable methodologies prove quite informative.32
The WHO stepwise approach to chronic disease risk factor surveillance (STEPS) The WHO stepwise approach to chronic disease risk factor surveillance (STEPS) focuses on obtaining core data on the established risk factors that underlie the major chronic disease burden.32 It was intentionally designed with the flexibility to permit each country to obtain the core variables and risk factors, and to expand to include optional modules based on country interest and need.32 Most importantly, the use of the same standardized questions and protocols by all participating countries enables appropriate comparisons across countries.32
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Fig 1 – The 10 leading diseases and injuries and 10 leading risk factors based on percentage of deaths and DALYs in subSaharan Africa, 2010. Reproduced with permission from The Institute of Health Metrics and Evaluation. Human Development Network, The World Bank. Generating Evidence, Guiding Policy – Sub-Saharan Africa Regional Edition. Seattle, WA: IHME, 2013. Institute for Health Metrics and Evaluation 2013. Note: This figure compares the percent of DALYs and deaths attributable to different diseases and injuries (shown in blue) as well as risk factors (shown in red). Certain causes, such as iron deficiency, cause more DALYs than they do deaths. DALYs are an important tool for decision-makers because they capture years of healthy life lost from both premature death and years lived with disability.
The three key steps of the survey tool includes Step 1 for the collection of basic demographic and behavioral and lifestyle factors such as tobacco and alcohol use; Step 2 for physical measurements such as height, weight, and blood pressure measurements; and Step 3 for biochemical assessments including fasting blood glucose and blood cholesterol.32 As shown in Table 1, the survey was last conducted as recently as 2012 for Lesotho and Tanzania but it had not been repeated since 2003 in Cameroon. Marked heterogeneity in the prevalence of major risk factors was seen. For example, the prevalence of current smoking was less than 5% in Ethiopia and Niger but greater than 20% in the Seychelles, Lesotho, and Sierra Leone. In all countries that had survey data, the proportion of participants who had none of the 3 major risk factors was less than 13%. In many of these countries, increasing BMI and hypertension are the primary cardiometabolic risk factors. In one recent publication from Malawi that used the STEPwise approach and measured blood pressure in 3,727 participants, the age-standardized prevalence of hypertension (BP ≥140/ 90 mm Hg) was 33.2%; three-quarters of the participants had never had their BP previously measured; and 94.9% of those with hypertension were unaware of the condition.33
The metabolic risk factors of chronic diseases The Global Burden of Metabolic Risk Factors of Chronic Diseases Collaborating Group recently published prevalence data and trends at the national, regional, and global levels for body mass index5 and adult overweight and obesity;6 fasting plasma glucose and diabetes;7 serum total cholesterol;8 and systolic blood pressure.9 The data represent up to 960 country-years and over 9.1 million men and women over age 20 years who participated in national health examination surveys and epidemiological studies in hypertension, diabetes, and their metabolic risks. Between 1980 and 2008, the age-standardized BMI increased in all geographic sub-regions of SSA except in central Africa.5 Overall, SSA (excluding South Africa) together with East, South, and Southeast Asia regions saw the smallest rise in BMI for men. However, in women, Southern Africa was among the subregions with the highest BMI in 2008.5 In fact, in 2008, the agestandardized prevalence of female obesity was highest in southern African women at 36.4%.6 Countries in SSA, especially east Africa, were among those with the lowest mean FPG in 2008. Importantly, however, none of the countries had a meaningful
Table 1 – Prevalence of selected chronic non-communicable disease risk factors and risk factor clusters in the WHO stepwise approach to chronic disease risk factor surveillance (STEPS) from selected African countries
Country
2008 2007 2003 2007 2010 2008 2011 2005 2004 2005 2004 2006 2009 2010 2009 2012 2011 2005 2009 2006 2005 2007 2008 2004 2009 2007 2012 2010 2008 2011
8.8 19.7 6.3 9.9 14.1 11.2 12.9 6.4 11.1 14.4 7.8 4.6 12.1 15.6 12.8 24.5 9.9 19.6 14.1 18.9 18.7 4.6 5.5 22.2 25.8 7.1 14.1 6.8 6.5 7.3
% Who Ate 3 of the CRFs, Ages 25–44 Years Old
% With >3 of the CRFs, Ages 45–64 Years Old
% With >3 of the CRFs, Ages 25–64 Years Old
3.0 13.9 12.7 21.0 4.8 20.8 5.2 6.3 19.2 5.6 6.2 3.8 22.5 6.5 9.5 14.5 9.1 2.6 4.6 3.8
7.9 13.0 25.9 9.8 4.6 8.7 24.4 2.1 7.5 59.7 5.8 26.0 14.2 23.8 24.5
11.0 1.2 5.0 12.2 0.3 5.9 5.3 4.9 0.8 0.3 1.2 2.1 7.9 2.2 1.1 12.8 1.0 2.4 0.9 6.4 4.2 1.4 1.9 0.8 2.4 1.0 0.6
9.5 25.7 19.6 12.3 22.8 18.5 19.9 24.5 13.5 17.2 30.0 20.7 15.4 22.1 28.7 12.1 13.0 14.0 17.5 15.6 29.9 22.7 30.4 12.2 13.1 16.6 18.9
21.8 50.4 41.8 29.4 37.3 32.3 34.0 44.3 26.1 34.2 50.0 39.8 35.2 41.6 43.2 17.7 23.7 28.6 26.8 36.1 52.1 37.2 47.8 28.0 23.7 46.8 38.1
14.9 34.5 24.8 17.7 27.8 23.0 24.1 30.1 19.4 36.4 25.8 21.6 26.7 33.5 13.8 16.5 19.0 21.4 22.1 38.8 27.0 35.5 16.6 16.1 23.7 24.2
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Source of Data: The World Health Organization. STEPS Country Reports. http://www.who.int/chp/steps/reports/en/. Last accessed on 21 May 2013. 1. Year of most recent STEPS survey; 2. Percentage who ate less than 5 combined servings of fruit and/or vegetables on average per day. 3. Percentage who are obese (BMI at least 30 kg/m2). 4. Percentage with raised BP (SBP at least 140 and/or DBP at least 90 mm Hg or currently on medication for raised BP). 5. Percentage with raised blood glucose as defined below or currently on medication for raised blood glucose: •plasma venous value _7.0 mmol/L or _126 mg/dl •capillary whole blood value _6.1 mmol/L or _110 mg/dl 4. Percentage with raised total blood cholesterol. 6. CRFs are the combined risk factors including (a) current daily smokers; (b) consumption of less than 5 servings of fruits and/or vegetables on average per day; (c) low level of activity (< 600 METminutes); (d) overweight (BMI at least 25 kg/m2); (e) raised BP (SBP at least 140 and/or DBP at least 90 mm Hg or currently on medication for raised BP).
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Benin Botswana Cameroon Cape Verde CAR Chad Comoros Congo, Dem. Rep. Congo, Brazzaville Cote d'Ivoire Eritrea Ethiopia Gabon Gambia, The Guinea Lesotho Liberia Madagascar Malawi Mauritania Mozambique Niger Sao Tome and Principe Seychelles Sierra Leone Swaziland Tanzania Togo Zambia Zanzibar
Year1
% Who Currently Smoke Tobacco
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decline in mean FPG.7 Similarly, at the national level in 2008, most of the countries worldwide that had the lowest mean total cholesterol were in SSA, and the trend over the period of observation in mean TC was flat.8 Although SBP declined at the global level by 1.0 mm Hg per decade in women and 0.8 mm Hg per decade in men between 1980 and 2008, it rose significantly in East Africa for both sexes and in West Africa for women.9 This is particularly important since SBP in women fell by as much as 3.5 mm Hg per decade or greater in Western Europe and Australasia, but it increased by as much as 1.0–2.7 mm Hg per decade in women in south and southeast Asia, and in east and west Africa.9 Consistent with these trends, the highest SBP levels in women were found in some East and West African countries, where the mean SBP of 135 mm Hg or greater exceeded the WHO theoretical minimum SBP by 20 mm Hg. Similarly, SBP in men was highest in some east and West African countries where the mean SBP was at least 138 mm Hg.9 These findings are consistent with the data from Lim et al. in the Global Burden of Diseases, Injuries, and Risk Factor Study discussed in the next section.4
The Global Burden of Diseases, Injuries, and Risk Factor (GBD 2010) Study The GBD 2010 Study estimated deaths and disability-adjusted life years (DALYs) attributable to the independent effects of 67 risk factors and clusters of risk factors for 21 regions in 1990 and 2010.4 At the global level in 2010, the three leading risk factors for disease burden were high blood pressure, tobacco smoking
including second-hand smoke, and household air pollution from solid fuels.4 For SSA as a whole, the leading risk factors for disease burden remained those associated with poverty, adverse maternal and child health, and dietary risks (Fig 2).4 As shown in Fig 3, for all but the Southern region of SSA, the four leading risk factors did not include the traditional risk factors for stroke, coronary heart disease, or diabetes but predominantly featured childhood underweight, household air pollution from solid fuels, suboptimal breastfeeding, and iron deficiency. High blood pressure ranked second in Southern Africa and was the fifth or sixth leading risk factor for the rest of SSA. Similarly, high body-mass index ranked third in Southern Africa but ranked fourteenth to eighteenth in the rest of SSA. Although high total cholesterol ranked 15th at the global level, it was relatively less prominent as a major risk factor in SSA where it ranked 27th to 30th except in Southern Africa where it ranked 19th. With the exception of physical inactivity and total cholesterol, all other major risk factors for CVD and diabetes ranked within the top 15 leading risk factors in 2010 and, in general, represented an increase in ranking compared to their status in 1990 (Fig 4). The ranking of DALYs attributable to the 25 leading risk factors for a group of countries in SSA in 2010 is shown in Fig 5.34 One important advantage of the GBD 2010 Study is the use of comparable methodology across all regions and in both time periods in 1990 and 2010. This affords us the opportunity to examine the trends in these risk factors and their relationship to health loss. As shown in Fig 6, the share of disease burden attributable to childhood underweight, household air pollution from solid fuels and suboptimal
Fig 2 – The burden of disease attributable to 20 leading risk factors in sub-Saharan Africa in 2010, expressed as a percentage of disability-adjusted life-years for both sexes in sub-Saharan Africa.
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Fig 3 – Leading risk factors ranked by attributable burden of disease at the global level and by region in sub-Saharan Africa in 2010. Regions are ordered by mean life expectancy. Modified from Lim SS, Vos T, Flaxman AD et al. A comparative risk assessment of burden of disease and injury attributable to 67 risk factors and risk factor clusters in 21 regions, 1990–2010: a systematic analysis for the Global Burden of Disease Study 2010. Lancet 2012 December 15;380(9859):2224–60, with permission from Elsevier.
breastfeeding has declined significantly, although they remain leading causes of health loss. On the other hand, high BMI and high systolic blood pressure increased at rates significantly higher than in other regions of the world as previously discussed.4,34
Implications for clinical and public health action It is often stated that non-communicable diseases are the leading cause of death worldwide and that nearly 80% of
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these deaths in both men and women occur in low- and middle-income countries.35 Additionally, more than 80% of global cardiovascular and diabetes related deaths also occur in low- and middle income countries.35 More importantly, the World Health Organization has estimated that the largest increase in non-communicable disease-related mortality over the next decade will also occur in these low- and middleincome countries. Since SSA countries are part of these lowand middle-income countries, it is often assumed that these patterns and associated “tsunami” of cardiovascular diseases, diabetes, and other non-communicable diseases apply equally and therefore of clinical and public health action to address the four main behavioral risk factors: tobacco use, physical inactivity, harmful use of alcohol and unhealthy diet must also be prioritized in SSA.35,36 The weight of the evidence reviewed however suggests that in SSA, the leading cause of total and premature mortality and disability is not cardiovascular diseases, diabetes, or other noncommunicable disease but rather communicable, maternal, neonatal, and nutritional causes and their related risk factors.4,11,34,37 Continued aggressive investments in the prevention, treatment, and control of these communicable, maternal, and nutritional conditions should remain paramount. Nevertheless, three strong, consistent, and ominous trends are evident in the review of the risk factors data. The rise in age-standardized BMI and increasing fasting plasma glucose portend an adverse trend in future diabetes and cardiovascular diseases. Second, the rising systolic BP in men, especially in eastern SSA, and in western SSA for women is ominous for future stroke, hypertensive heart disease, and other cardiovascular diseases. Third, the relatively moderate-to-high proportion of persons with at least one of the combined risk factors of
(1) current daily smokers; (2) consumption of less than 5 servings of fruits and/or vegetables on average per day; (3) low level of activity (
Available online at www.sciencedirect.com
ScienceDirect www.onlinepcd.com
Descriptive Epidemiology of Cardiovascular Risk Factors and Diabetes in Sub-Saharan Africa George A. Mensah⁎ Office of the Director, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD
A R T I C LE I N FO
AB S T R A C T
Keywords:
Reliable data on risk factor levels, exposure history, and population distribution can help
Cardiovascular diseases
inform policies and programs for disease prevention and control. With rare exception
Sub-Saharan Africa
however, ideal local data on major risk factors and causes of death and disease burden have
Cardiovascular risk factors
been scarce in sub-Saharan Africa (SSA). Basic community surveys in some countries and recent systematic analysis of disease burden attributable to 67 risk factors and risk factor clusters in 21 regions of the world provide an opportunity to examine and relate diabetes and cardiovascular risk factors to mortality and burden in SSA. Rising body mass index, especially in women in Southern Africa; and rising systolic blood pressure in East Africa for both sexes, and in West Africa for women are the major cardiometabolic risk factors. Harmful use of alcohol, especially in Southern SSA, tobacco use, and physical inactivity are also important. Improving vital registration and risk factor surveillance remain major challenges. Published by Elsevier Inc.
The landmark Framingham Heart Study introduced the concept that current or past exposure to specific factors increases the risk of future cardiovascular disease.1 These “factors of risk” are now well described for coronary heart disease, stroke, other cardiovascular diseases (CVD), and diabetes and are the same in sub-Saharan Africa (SSA) as they are in other parts of the world. These risk factors include high blood pressure (BP); tobacco use, including exposure to second-hand smoke; harmful use of alcohol; high total blood cholesterol; high fasting plasma glucose (FPG); high body mass index (BMI); high intake of dietary sodium; low dietary intake of fruits and vegetables; low physical activity; and household and ambient air pollution.
Statement of Conflict of Interest: see page: 248. Disclaimer: The views expressed in this article do not necessarily represent the views of the National Heart, Lung, and Blood Institute, National Institutes of Health, Department of Health and Human Services or any other government entity. ⁎ Address reprint requests to George A. Mensah, NIH/NHLBI/IOD, 31 Center Drive MSC 2486, Bethesda, MD 20892-2490. E-mail address: [email protected]. 0033-0620/$ – see front matter. Published by Elsevier Inc. http://dx.doi.org/10.1016/j.pcad.2013.10.014
Together, known risk factors explain the majority of the population burden of total CVD. For example, Yusuf et al. showed that nine potentially modifiable risk factors collectively accounted for 90% and 94% of the population attributable risk for first-time acute myocardial infarction (AMI) in men and women, respectively in 52 countries.2 In the African population of the INTERHEART Study, five risk factors (smoking history, diabetes history, hypertension history, abdominal obesity, and ratio of apolipoprotein B to apolipoprotein A-1) contributed a similar population attributable risk of nearly 90% for AMI.3 In general, the magnitude and duration of exposure to these risk factors determine the level of risk of future disease-related outcomes. Thus, accurate and reliable information on risk factor levels and their population distribution can help inform policies and programs for prevention, treatment, and control. With rare exception however, ideal and reliably enumerated epidemiological data on these major risk factors have not been readily available in SSA. Recent completion of the systematic analysis of the burden of disease and injury attributable to 67 risk factors and risk factor clusters in 21 regions of the world including
PR O G RE S S I N C ARDI O V A S CU L A R D I S EA S E S 5 6 (2 0 1 3) 24 0–2 5 0
Abbreviations and Acronyms
four regions in SSA, and other global burBMI = body mass index den of disease BP = blood pressure assessments4–12 provide a unique opporCHD = Coronary heart disease tunity to examine and CVD = Cardiovascular disease relate these risk factors to mortality and DALY = disability-adjusted life disease burden in SSA year using comparable FPG = fasting plasma glucose methodology. Progress made in the GBD = Global Burden of Diseases World Health OrganiSSA = sub-Saharan Africa zation’s STEPS chronic disease risk factor STEPS = Stepwise approach to surveillance in this rechronic non-communicable disgion is also reviewed ease surveillance together with previTC = Total cholesterol ously published data from specific risk facWHO = World Health tor studies in SSA. Organization Although the focus of this article is CVD and diabetes, it must be emphasized that in most of SSA, the leading threats to health continue to be those associated with poverty and maternal and child mortality as shown in Fig 1.4 However, the ongoing health transitions together with adverse impact of globalization and urbanization13–17 in SSA make it necessary to promote the development of the capacity to monitor the magnitude and trends in diabetes18–20 and CVD4,21 risk factors in order to better inform programs and policies for the prevention and control of diabetes and CVD in SSA.
CVD risk factors in sub-Saharan Africa – the background A high prevalence of adverse CHD risk factors in the nineteenth and early twentieth centuries in SSA seems very unlikely given the rarity of CHD in the published historical data from western, eastern, central, and southern Africa from that period.22 For example, extensive review of the Annual Medical and Sanitary Reports sent regularly to the Colonial Secretary in London by the Nigerian and Gold Coast governments showed that coronary heart disease was distinctly rare from 1898 to 1960.23–25 Since the turn of the twenty-first century however, the weight of the published data suggests that diabetes and CVD risk factors are increasing in prevalence in SSA in men and women, and in children and adults. For example, in a birth cohort study of CVD risk factors in 5-yearold children living in an urban environment in South Africa in 1990, Steyn et al.26 showed that overall, 64% of the children were already exposed to environmental tobacco smoke with the highest exposures observed in colored children; among these colored children, 42% lived in homes with two or more smokers.26 Significant ethnic differences observed included significantly higher blood pressure in black children in whom diastolic blood pressure levels were also the highest.
241
A similarly high CVD risk factor prevalence was observed in a random population-based sample of 976 people aged 15 years and older in a peri-urban working-class community in South Africa.27 Hypertension prevalence was 22% in men and 16% in women; 62% of men and 44% of women smoked cigarettes; hypercholesterolemia was present in nearly half of the population (47% of men, and 46% of women); while diabetes was prevalent in 6% of men and 5% of women.27 In the predominantly Black African community of Soweto, Tibarzawa et al.28 showed that nearly 78% of subjects had at least one major CVD risk factor. The most prevalent CVD and diabetes risk factor in this middle-aged adult population was obesity (43%) with nearly a 2-fold greater prevalence in women than in men.28 Additionally, 33% of subjects had high systolic or diastolic blood pressures, and 13% had elevated (non-fasting) total blood cholesterol level. Importantly, overweight subjects were three times more likely to have concurrent hypercholesterolemia.28 This relatively high burden of CVD risk factors and diabetes in population sub-groups in South Africa should not be assumed to be representative of the rest of SSA because of the relatively more advanced stage of epidemiologic, socioeconomic, and nutritional transition in South Africa compared to other parts of SSA.29 Nevertheless, the trend of increasing prevalence in CVD risk factors in most countries where studies have been performed is unmistakable.30 An important limitation in making international and inter-regional comparisons is the wide heterogeneity of studies and differences in sample sizes, sampling methodologies, diagnostic approaches and criteria; different age distributions; and different study settings with varying representation of rural and urban populations. For example, in the recent systematic review of the evidence on the prevalence and pathogenesis of type 2 diabetes published in Africa over the past decade, Kengne et al.31 identified 13 community-based studies from nine SSA countries and Tunisia. They found a ten-fold difference in reported diabetes prevalence ranging from 2.8% in rural Angola to 28.2% in an urban population setting in South Africa.31 Similarly, the reported prevalence of obesity in 20 studies they identified ranged from 5% in rural Uganda to 30% in urban Nigeria.31 Their overall assessment of the quality of these data was that, in general, these data do not provide accurate estimates of the magnitude of the conditions studied. It is in this regard that the WHO stepwise approach to chronic non-communicable disease surveillance (STEPS) and other studies that use comparable methodologies prove quite informative.32
The WHO stepwise approach to chronic disease risk factor surveillance (STEPS) The WHO stepwise approach to chronic disease risk factor surveillance (STEPS) focuses on obtaining core data on the established risk factors that underlie the major chronic disease burden.32 It was intentionally designed with the flexibility to permit each country to obtain the core variables and risk factors, and to expand to include optional modules based on country interest and need.32 Most importantly, the use of the same standardized questions and protocols by all participating countries enables appropriate comparisons across countries.32
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Fig 1 – The 10 leading diseases and injuries and 10 leading risk factors based on percentage of deaths and DALYs in subSaharan Africa, 2010. Reproduced with permission from The Institute of Health Metrics and Evaluation. Human Development Network, The World Bank. Generating Evidence, Guiding Policy – Sub-Saharan Africa Regional Edition. Seattle, WA: IHME, 2013. Institute for Health Metrics and Evaluation 2013. Note: This figure compares the percent of DALYs and deaths attributable to different diseases and injuries (shown in blue) as well as risk factors (shown in red). Certain causes, such as iron deficiency, cause more DALYs than they do deaths. DALYs are an important tool for decision-makers because they capture years of healthy life lost from both premature death and years lived with disability.
The three key steps of the survey tool includes Step 1 for the collection of basic demographic and behavioral and lifestyle factors such as tobacco and alcohol use; Step 2 for physical measurements such as height, weight, and blood pressure measurements; and Step 3 for biochemical assessments including fasting blood glucose and blood cholesterol.32 As shown in Table 1, the survey was last conducted as recently as 2012 for Lesotho and Tanzania but it had not been repeated since 2003 in Cameroon. Marked heterogeneity in the prevalence of major risk factors was seen. For example, the prevalence of current smoking was less than 5% in Ethiopia and Niger but greater than 20% in the Seychelles, Lesotho, and Sierra Leone. In all countries that had survey data, the proportion of participants who had none of the 3 major risk factors was less than 13%. In many of these countries, increasing BMI and hypertension are the primary cardiometabolic risk factors. In one recent publication from Malawi that used the STEPwise approach and measured blood pressure in 3,727 participants, the age-standardized prevalence of hypertension (BP ≥140/ 90 mm Hg) was 33.2%; three-quarters of the participants had never had their BP previously measured; and 94.9% of those with hypertension were unaware of the condition.33
The metabolic risk factors of chronic diseases The Global Burden of Metabolic Risk Factors of Chronic Diseases Collaborating Group recently published prevalence data and trends at the national, regional, and global levels for body mass index5 and adult overweight and obesity;6 fasting plasma glucose and diabetes;7 serum total cholesterol;8 and systolic blood pressure.9 The data represent up to 960 country-years and over 9.1 million men and women over age 20 years who participated in national health examination surveys and epidemiological studies in hypertension, diabetes, and their metabolic risks. Between 1980 and 2008, the age-standardized BMI increased in all geographic sub-regions of SSA except in central Africa.5 Overall, SSA (excluding South Africa) together with East, South, and Southeast Asia regions saw the smallest rise in BMI for men. However, in women, Southern Africa was among the subregions with the highest BMI in 2008.5 In fact, in 2008, the agestandardized prevalence of female obesity was highest in southern African women at 36.4%.6 Countries in SSA, especially east Africa, were among those with the lowest mean FPG in 2008. Importantly, however, none of the countries had a meaningful
Table 1 – Prevalence of selected chronic non-communicable disease risk factors and risk factor clusters in the WHO stepwise approach to chronic disease risk factor surveillance (STEPS) from selected African countries
Country
2008 2007 2003 2007 2010 2008 2011 2005 2004 2005 2004 2006 2009 2010 2009 2012 2011 2005 2009 2006 2005 2007 2008 2004 2009 2007 2012 2010 2008 2011
8.8 19.7 6.3 9.9 14.1 11.2 12.9 6.4 11.1 14.4 7.8 4.6 12.1 15.6 12.8 24.5 9.9 19.6 14.1 18.9 18.7 4.6 5.5 22.2 25.8 7.1 14.1 6.8 6.5 7.3
% Who Ate 3 of the CRFs, Ages 25–44 Years Old
% With >3 of the CRFs, Ages 45–64 Years Old
% With >3 of the CRFs, Ages 25–64 Years Old
3.0 13.9 12.7 21.0 4.8 20.8 5.2 6.3 19.2 5.6 6.2 3.8 22.5 6.5 9.5 14.5 9.1 2.6 4.6 3.8
7.9 13.0 25.9 9.8 4.6 8.7 24.4 2.1 7.5 59.7 5.8 26.0 14.2 23.8 24.5
11.0 1.2 5.0 12.2 0.3 5.9 5.3 4.9 0.8 0.3 1.2 2.1 7.9 2.2 1.1 12.8 1.0 2.4 0.9 6.4 4.2 1.4 1.9 0.8 2.4 1.0 0.6
9.5 25.7 19.6 12.3 22.8 18.5 19.9 24.5 13.5 17.2 30.0 20.7 15.4 22.1 28.7 12.1 13.0 14.0 17.5 15.6 29.9 22.7 30.4 12.2 13.1 16.6 18.9
21.8 50.4 41.8 29.4 37.3 32.3 34.0 44.3 26.1 34.2 50.0 39.8 35.2 41.6 43.2 17.7 23.7 28.6 26.8 36.1 52.1 37.2 47.8 28.0 23.7 46.8 38.1
14.9 34.5 24.8 17.7 27.8 23.0 24.1 30.1 19.4 36.4 25.8 21.6 26.7 33.5 13.8 16.5 19.0 21.4 22.1 38.8 27.0 35.5 16.6 16.1 23.7 24.2
243
Source of Data: The World Health Organization. STEPS Country Reports. http://www.who.int/chp/steps/reports/en/. Last accessed on 21 May 2013. 1. Year of most recent STEPS survey; 2. Percentage who ate less than 5 combined servings of fruit and/or vegetables on average per day. 3. Percentage who are obese (BMI at least 30 kg/m2). 4. Percentage with raised BP (SBP at least 140 and/or DBP at least 90 mm Hg or currently on medication for raised BP). 5. Percentage with raised blood glucose as defined below or currently on medication for raised blood glucose: •plasma venous value _7.0 mmol/L or _126 mg/dl •capillary whole blood value _6.1 mmol/L or _110 mg/dl 4. Percentage with raised total blood cholesterol. 6. CRFs are the combined risk factors including (a) current daily smokers; (b) consumption of less than 5 servings of fruits and/or vegetables on average per day; (c) low level of activity (< 600 METminutes); (d) overweight (BMI at least 25 kg/m2); (e) raised BP (SBP at least 140 and/or DBP at least 90 mm Hg or currently on medication for raised BP).
PR O G RE S S I N C ARDI O V A S CU L A R D I S EA S E S 5 6 (2 0 1 3) 24 0–2 5 0
Benin Botswana Cameroon Cape Verde CAR Chad Comoros Congo, Dem. Rep. Congo, Brazzaville Cote d'Ivoire Eritrea Ethiopia Gabon Gambia, The Guinea Lesotho Liberia Madagascar Malawi Mauritania Mozambique Niger Sao Tome and Principe Seychelles Sierra Leone Swaziland Tanzania Togo Zambia Zanzibar
Year1
% Who Currently Smoke Tobacco
244
PR O GRE S S I N C ARDI O VAS CU L AR D I S EAS E S 5 6 ( 2 0 13 ) 24 0–2 50
decline in mean FPG.7 Similarly, at the national level in 2008, most of the countries worldwide that had the lowest mean total cholesterol were in SSA, and the trend over the period of observation in mean TC was flat.8 Although SBP declined at the global level by 1.0 mm Hg per decade in women and 0.8 mm Hg per decade in men between 1980 and 2008, it rose significantly in East Africa for both sexes and in West Africa for women.9 This is particularly important since SBP in women fell by as much as 3.5 mm Hg per decade or greater in Western Europe and Australasia, but it increased by as much as 1.0–2.7 mm Hg per decade in women in south and southeast Asia, and in east and west Africa.9 Consistent with these trends, the highest SBP levels in women were found in some East and West African countries, where the mean SBP of 135 mm Hg or greater exceeded the WHO theoretical minimum SBP by 20 mm Hg. Similarly, SBP in men was highest in some east and West African countries where the mean SBP was at least 138 mm Hg.9 These findings are consistent with the data from Lim et al. in the Global Burden of Diseases, Injuries, and Risk Factor Study discussed in the next section.4
The Global Burden of Diseases, Injuries, and Risk Factor (GBD 2010) Study The GBD 2010 Study estimated deaths and disability-adjusted life years (DALYs) attributable to the independent effects of 67 risk factors and clusters of risk factors for 21 regions in 1990 and 2010.4 At the global level in 2010, the three leading risk factors for disease burden were high blood pressure, tobacco smoking
including second-hand smoke, and household air pollution from solid fuels.4 For SSA as a whole, the leading risk factors for disease burden remained those associated with poverty, adverse maternal and child health, and dietary risks (Fig 2).4 As shown in Fig 3, for all but the Southern region of SSA, the four leading risk factors did not include the traditional risk factors for stroke, coronary heart disease, or diabetes but predominantly featured childhood underweight, household air pollution from solid fuels, suboptimal breastfeeding, and iron deficiency. High blood pressure ranked second in Southern Africa and was the fifth or sixth leading risk factor for the rest of SSA. Similarly, high body-mass index ranked third in Southern Africa but ranked fourteenth to eighteenth in the rest of SSA. Although high total cholesterol ranked 15th at the global level, it was relatively less prominent as a major risk factor in SSA where it ranked 27th to 30th except in Southern Africa where it ranked 19th. With the exception of physical inactivity and total cholesterol, all other major risk factors for CVD and diabetes ranked within the top 15 leading risk factors in 2010 and, in general, represented an increase in ranking compared to their status in 1990 (Fig 4). The ranking of DALYs attributable to the 25 leading risk factors for a group of countries in SSA in 2010 is shown in Fig 5.34 One important advantage of the GBD 2010 Study is the use of comparable methodology across all regions and in both time periods in 1990 and 2010. This affords us the opportunity to examine the trends in these risk factors and their relationship to health loss. As shown in Fig 6, the share of disease burden attributable to childhood underweight, household air pollution from solid fuels and suboptimal
Fig 2 – The burden of disease attributable to 20 leading risk factors in sub-Saharan Africa in 2010, expressed as a percentage of disability-adjusted life-years for both sexes in sub-Saharan Africa.
PR O G RE S S I N C ARDI O V A S CU L A R D I S EA S E S 5 6 (2 0 1 3) 24 0–2 5 0
245
Fig 3 – Leading risk factors ranked by attributable burden of disease at the global level and by region in sub-Saharan Africa in 2010. Regions are ordered by mean life expectancy. Modified from Lim SS, Vos T, Flaxman AD et al. A comparative risk assessment of burden of disease and injury attributable to 67 risk factors and risk factor clusters in 21 regions, 1990–2010: a systematic analysis for the Global Burden of Disease Study 2010. Lancet 2012 December 15;380(9859):2224–60, with permission from Elsevier.
breastfeeding has declined significantly, although they remain leading causes of health loss. On the other hand, high BMI and high systolic blood pressure increased at rates significantly higher than in other regions of the world as previously discussed.4,34
Implications for clinical and public health action It is often stated that non-communicable diseases are the leading cause of death worldwide and that nearly 80% of
246
PR O GRE S S I N C ARDI O VAS CU L AR D I S EAS E S 5 6 ( 2 0 13 ) 24 0–2 50
these deaths in both men and women occur in low- and middle-income countries.35 Additionally, more than 80% of global cardiovascular and diabetes related deaths also occur in low- and middle income countries.35 More importantly, the World Health Organization has estimated that the largest increase in non-communicable disease-related mortality over the next decade will also occur in these low- and middleincome countries. Since SSA countries are part of these lowand middle-income countries, it is often assumed that these patterns and associated “tsunami” of cardiovascular diseases, diabetes, and other non-communicable diseases apply equally and therefore of clinical and public health action to address the four main behavioral risk factors: tobacco use, physical inactivity, harmful use of alcohol and unhealthy diet must also be prioritized in SSA.35,36 The weight of the evidence reviewed however suggests that in SSA, the leading cause of total and premature mortality and disability is not cardiovascular diseases, diabetes, or other noncommunicable disease but rather communicable, maternal, neonatal, and nutritional causes and their related risk factors.4,11,34,37 Continued aggressive investments in the prevention, treatment, and control of these communicable, maternal, and nutritional conditions should remain paramount. Nevertheless, three strong, consistent, and ominous trends are evident in the review of the risk factors data. The rise in age-standardized BMI and increasing fasting plasma glucose portend an adverse trend in future diabetes and cardiovascular diseases. Second, the rising systolic BP in men, especially in eastern SSA, and in western SSA for women is ominous for future stroke, hypertensive heart disease, and other cardiovascular diseases. Third, the relatively moderate-to-high proportion of persons with at least one of the combined risk factors of
(1) current daily smokers; (2) consumption of less than 5 servings of fruits and/or vegetables on average per day; (3) low level of activity (
