Population health

Global statistics show that we are healthier and live longer than ever before. This substantial progress results from major advancements in public health and health care (e.g., health systems), including improved hygiene practices, health education, legislative changes, and technological developments, such as vaccination. Many recent health gains resulted from exploitation of natural resources, particularly for food and energy provision. Advancements in human health were critical for the human “great escape” out of poverty over the past 250 years (Deaton, 2013) as Figure 2.17 shows, leading to today’s unprecedented levels of high global life expectancy and increasing survival of children under five years.

Despite significant overall progress, substantial improvements are still needed. Massive health inequalities continue to exist, and in some cases are widening, within and between countries.

For example, average life expectancy varies between 50 years in Sierra Leone to 84 years in Japan, and children are 14 times more likely to die before the age of five in sub-Saharan Africa than in the rest of the world (UNICEF and WHO, 2017). Further, in recent years, life expectancy appears to be declining in the US (CDC, 2018) and the UK (Office for National Statistics, 2017).

Figure 2.18 shows how the burden of disease measured in disability-adjusted life years (DALYs) for men and women changed from 1990 to 2006 to 2016 (Gakidou et al., 2017).

Environmental, social, and political transformations can affect health directly and indirectly. We focus on critical dynamic trends already detrimentally affecting the health of specific populations: global aging, maternal and child health

Figure 2.17. Major advancements for human health 1740 – today. Source: Provided by courtesy of Pauline Scheelbeek.

improvements, emerging and re-emerging infectious diseases, the growing prevalence of non-communicable diseases, and urbanization. Several of the trends and health outcomes described are linked to global sustainability and could be negatively affected by climatic changes (Ebi et al., 2018). If not adequately addressed, these challenges will influence future

health trajectories. Health is a cross-cutting issue throughout the SDGs, as changes in health impact the trajectories of other SDGs (and vice-versa).

Global aging

A key health challenge that countries around the world are

Figure 2.18. Leading 30 risk factors by attributable DALYs at the global level. Years 1990, 2006, and 2016 for males (A) and females (B). Risks are connected by lines between time periods. Behavioral risk factors are shown in red, environmental risk factors in blue, and metabolic risk in green. Source: Licensed under CC BY 4.0 by Gakidou et al. (2017).

beginning to and will continue to confront is population aging.

As global fertility rates continue to decline and life expectancies lengthen, the median age is increasing throughout the world, although some countries, particularly those in East Asia and Europe, will be disproportionately affected (Lutz et al., 2017).

Aging populations, particularly an increase in those over 75 years of age, will create sizable challenges for health systems due to greater burdens associated with non-communicable diseases and providing more frequent and expensive treatments for an older population, leading to increased overall health expenditure (WHO, 2015b). Although the retirement age is increasing in many parts of the world, people over 75 years of age are less likely to work, and could impose an economic burden on families and society (Bloom et al., 2015). Governments will have to grapple with how to address rising health care costs while continuing to fund other needed services.

Figure 2.19 shows the contribution of population growth and aging to the percent change in deaths and DALYs at the global level, 2006-2016.

Maternal, newborn, child, and adolescent health

Achieving a healthy world depends on improving the health of women, children, and adolescents. Investing in early childhood development is one of the best investments in boosting economic growth, promoting sustainable societies, and eliminating extreme poverty and inequality. Transforming maternal and child health will require efforts in the coming decades to increase education of women, address threats to the quality and quantity of our food and water, improve the quality and coverage of health systems, and promote nurturing care.

Maternal mortality (deaths due to complications from pregnancy or childbirth) fell by 44% between 1990 and 2015 (WHO, 2015b). However, this is less than what is needed to achieve the maternal mortality target for SDG 5 (Good Health and Wellbeing). Almost all maternal deaths are preventable. The lifetime risk of maternal death in high-income countries is 1 to 3,300 compared with 1 to 41 in low-income countries.

While significant progress in reducing childhood mortality has occurred over the past two decades, much remains to be

done. In 2016, 5.6 million children under the age of 5 years died (excluding newborns within their first year of life), roughly 15,000 deaths per day (UNICEF et al., 2017b). Yet, other information confirms that most of these deaths were in the first year of life. More than half of under-5 childhood deaths were due to diseases that are preventable and treatable.

During the past few decades, the world has taken significant steps towards improving child nutrition, with child stunting prevalence nearly halving from 39.5% in 1990 to 22.9% in 2016 (UNICEF et al., 2017a). Despite this progress, key challenges remain. In 2011, 1 in 3 people worldwide were affected by some form of malnutrition (including undernutrition, over nutrition and micronutrient deficiencies), 50 million children suffered from acute undernutrition (wasting) and 3 million children died from hunger (Horton and Lo, 2013). All aspects of food security will potentially be affected by climate change, including food access, utilization, food quality, and price stability, challenging continued progress on reducing undernutrition (Porter et al., 2014).

Most childhood diarrheal disease results from inadequate access to safe water and improved sanitation. It is estimated that 1.2 billion people gained access to piped water supply between 2000 and 2015 (UNICEF and WHO, 2017). There are still around 2.3 billion people who do not use improved sanitation and 844 million who do not have access to improved water sources, concentrated among rural populations with fewer resources and among fragile states (UNICEF and WHO, 2017).

Moreover, in low-income countries, almost 90% of sewage is discharged without any treatment and some countries also continue to release wastewater to the environment without sufficient treatment (Baum et al., 2013). These practices increase the risk of childhood diarrheal disease.

Emerging and re-emerging vector-borne, zoonotic, and other infectious diseases

The radical transition in the contribution of infectious diseases to population health is one of the hallmarks of the 21st century.

The global burden of infectious diseases has likely never been lower (Figure 2.20), and progress indicators across a range of key infectious disease categories continue to climb (Figure 2.21).

Despite these positive trends, infectious diseases continue to present a serious global health threat. For example, more than 1 billion cases and around 1 million deaths occur annually from vector-borne diseases alone (Campbell-Lendrum et al., 2015;

Kilpatrick and Randolph, 2012), and the incidence, impacts or geographic range of several high impact diseases have increased globally (e.g., dengue, zika) (Stanaway et al., 2016). Additionally, the rate of novel disease emergence has grown (Fisher et al., 2012; Jones et al., 2008). Many of these increases in risk have been linked to a range of large-scale and rapid environmental and socio-demographic changes that have occurred in recent decades. These include climate change, land-use change such as deforestation and agricultural expansion, social and development trends including increasing international travel and trade, and widespread use of antimicrobials (Semenza et al., 2016).

Figure 2.19. Percent change in deaths and DALYs at the global level. From 2006-2016, due to population growth, population aging, trends in exposures to all risks included in the 2016 Global Burden of Disease study, and all other factor. Source: Licensed under CC BY 4.0 by Gakidou et al. (2017).

Climatic changes have affected some infectious disease vectors or reservoirs, and in some cases have contributed to a rise or redistribution of infectious disease risks. The dramatic rise in dengue cases in the past few decades, for example, may be at least partially linked to improved environmental conditions for disease transmission or to increases in the geographic range of vector populations (Watts et al. 2017). Given that warming of nearly 1.5°C above preindustrial temperatures is projected to occur by about 2030-2040, increases in the burden of climate-sensitive health outcomes are very likely, with the magnitude and relative burdens dependent on the extent to which proactive and effective adaptation policies and measures are implemented (Ebi et al., 2018). In other cases, climatic changes are likely to have reduced disease risks as conditions suitable for transmission, vectors, or reservoir hosts are pushed beyond their climatic optima (Escobar et al., 2016). Determining the balance and geographic distribution of increases versus decreases in disease risk attributable to recent and projected climatic changes is an important scientific challenge for the Anthropocene.

Major environmental and social pressures and challenges embedded in the SDGs could also directly or indirectly influence

infectious disease risks. Ongoing changes to food production systems, including intensification and pest control, are contributing to antimicrobial resistant strains of pathogens that are poised to reverse a long period of gains in intensive disease control (Holmes et al., 2016). Urbanization, while typically associated with improved health outcomes, can contribute to rises in some infectious disease risks (Tian et al., 2018). Land-use change for agricultural and socioeconomic development (including urbanization and road networks) will continue to drive contact between disease hosts/vectors and humans, resulting in yet further opportunities for disease emergence and spread (Murray et al., 2016; Jones et al., 2013). However, such trends could be partially offset, as vectors and hosts themselves become casualties from habitat loss or fragmentation (Cable et al., 2017).

Moreover, increa sing globalization – in both passenger travel and international trade – has increased the likelihood of country-to-country spread of infectious diseases. At best, these processes will produce repeated disease introductions, sustain or promote transmission of endemic infections, and catalyze limited, albeit unpredictable, epidemics (e.g., 2014 Ebola

Low Low−middle Middle High−middle High

1990 2000 2010 1990 2000 2010 1990 2000 2010 1990 2000 2010 1990 2000 2010 0

100 200 300

Year

Global Burden of Disease (DALYs, millions)

Malaria and NTDs Diarrhea and lower respiratory HIV

TB Other IDs

Figure 2.20. Breakdown of the proportion of the global burden of infectious diseases (as measured by DALYs) by income category and cause. Source: Provided by courtesy of Kris Murray / Imperial College London. Data source: Institute for Health Metrics and Evaluation, University of Washington.

Sanitation TB Vaccine Coverage

HIV Malaria NTDs

1990 1995 2000 2005 2010 2015 1990 1995 2000 2005 2010 2015 1990 1995 2000 2005 2010 2015 25

50 75 100

25 50 75 100

Year

Progress Indicator (0=worst, 100=best)

continent Africa Americas Asia Europe Oceania

Figure 2.21. Trends in selected infectious disease progress indicators 1990-2015 by continent. Source: Provided by courtesy of Kris Murray / Imperial College London. Data source: Lim et al. (2016).

outbreak). At worst, they could help facilitate a global pandemic (Morse et al., 2012).

Increasing prevalence of non-communicable diseases Non-communicable diseases (NCDs) include an array of serious health conditions, including cardiovascular diseases, cancers, diabetes, and chronic lung diseases. In 2015, 70%

of deaths worldwide were due to NCDs, including 45% from cardiovascular diseases, and 22% from cancers. Over three-quarters of NCD mortality occurred in low- and middle-income countries, with about 48% occurring before the age of 70 (WHO, 2015b). This results in a ‘double-burden’ of disease, with high rates of communicable and NCDs in lower income countries. Major risk factors for NCDs include the environment (e.g., air pollution, Landrigan et al 2018), older age, unhealthy behaviors (e.g., poor diets, tobacco use, alcohol consumption and lack of physical activity), and metabolic factors (e.g., high blood pressure, obesity, and high blood glucose), often also related to diets.

Despite the world producing enough food from a caloric intake perspective, the food system is failing to deliver nutritious and healthy diets to all. Global diets are rapidly shifting towards processed and animal-source foods. Dietary factors now account for eight of the top twelve leading causes of death globally.

Consumption of animal- source foods is increasing, which, combined with excess food consumption, is resulting in greater natural resource use than is needed for healthy, balanced diets (Aleksandrowicz et al., 2016; Green et al., 2015). The number of overweight/obese people in low- and middle-income countries more than tripled between 1980 and 2008: from 250 million to 904 million (Keats and Wiggins, 2017).

Urbanization

Population growth in recent decades has been concentrated in cities, with more than half of the world’s population now living in urban areas (UNDESA, 2018). On average, urban environments may provide net benefits for health and wealth (an ‘urban advantage’) because of factors such as improved access to services (including health care, employment and education), better sanitation, and lower levels of malnutrition.

However, rapid urban development has also resulted in a wide range of social and environmental problems. In some regions, most notably sub-Saharan Africa, urbanization has not been accompanied by significant economic development, with negative effects on health. Health outcomes in areas of urban disadvantage, particularly in urban slums, may be much worse than in other urban areas (Ezeh et al., 2017). Moreover, heat islands (areas of higher temperature associated with the built environment) are associated with adverse health outcomes.

Greater urban sprawl may exacerbate these effects (Stone et al., 2010), although effective planning and urban design that emphasizes green spaces can mitigate these challenges (Kleerekoper et al., 2012).

2 This section is largely based on the entry of Goujon, A. V. 2018. Human Population Growth. In: Fath, B. (ed.) Encyclopedia of Ecoloogy. 2nd ed.: Elsevier.

Summary and conclusion

The status of population health and health systems in 2050 will depend on the interactions in the intervening decades among the trends discussed in this and other sections. Focusing only on health trends without considering trends in agriculture, demographics, land use, freshwater quality and availability, technology development, and other factors would provide a misleading picture of what is needed in order to improve health over coming decades. Understanding the implications of the interactions and magnitudes of these trends for health requires systems-based projections. Effective, proactive policies and measures, and increased investment in research, development, and implementation could lead to continuing improvements in health.