Health and Environment

Spec mapping (AQA 7037): Paper 2, §3.2.4 Population and the Environment — the relationship between the physical environment and human health; the global pattern of health, mortality and morbidity; the epidemiological transition; the link between development and health; the environmental, social and economic determinants of health; communicable and non-communicable diseases. This lesson extends the demographic work of Lessons 1–2 (mortality and life expectancy are health outcomes) into the geography of health and disease, and sets up the disease and global-health-governance lesson that follows. It links synoptically to §3.2.1 Global Systems and Global Governance (health is shaped by global flows, inequality and institutions such as the WHO) and to §3.1.1 Water and Carbon Cycles (climate and water quality are primary environmental determinants of health, and climate change is altering disease distributions). Assessment objectives: AO1 — knowledge of health measures, Omran's epidemiological transition, and the environmental, social and economic determinants of health; AO2 — application to real contexts (UK air pollution, sub-Saharan malaria, the Marmot social gradient); AO3 — interpretation and evaluation of health and disease data to reach a substantiated judgement.

This lesson examines global patterns of health and disease, Omran's epidemiological transition model (1971), the distinction between communicable and non-communicable diseases, and the environmental, social and economic determinants of health. Understanding why health outcomes vary so sharply between and within places is central to the Population and the Environment option.

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Measuring Health

Before analysing patterns, it is important to understand how health is measured at population level:

Indicator	Definition	Significance
Life expectancy at birth	Average years a newborn is expected to live	Overall health and development indicator
Infant Mortality Rate (IMR)	Deaths under age 1 per 1,000 live births	Sensitive indicator of healthcare quality, nutrition, and sanitation
Under-5 Mortality Rate	Deaths under age 5 per 1,000 live births	Broader child health measure
Maternal Mortality Ratio (MMR)	Maternal deaths per 100,000 live births	Quality of reproductive healthcare
DALYs (Disability-Adjusted Life Years)	Years of healthy life lost to disease or disability	Captures burden of non-fatal conditions
Morbidity rate	Prevalence or incidence of disease	Measures illness, not just death

Global Health Disparities

Country/Region	Life Expectancy (2023)	IMR (per 1,000)	Key Health Challenges
Japan	84.8 years	1.8	Ageing population, mental health
UK	80.7 years	3.7	Obesity, NHS pressures, health inequalities
USA	77.5 years	5.4	Obesity, opioid crisis, healthcare inequality
India	70.8 years	27.4	Communicable diseases, malnutrition, air pollution
Nigeria	53.9 years	72.2	Malaria, maternal mortality, weak healthcare infrastructure
Sierra Leone	54.7 years	78.5	Poverty, Ebola aftermath, limited healthcare

Exam Tip: Health inequalities exist not just between countries but within them. In the UK, life expectancy varies by up to 10 years between the most and least deprived areas (e.g., Blackpool vs. Hart district in Hampshire). Always consider intra-national health inequalities for a more nuanced analysis.

These indicators are not interchangeable, and choosing the right one is itself an AO3 skill. Life expectancy is the broadest summary but is dominated by deaths in infancy (a few infant deaths drag the average down sharply) and tells you nothing about quality of life. The infant mortality rate is the most sensitive indicator of a population's underlying conditions — it responds quickly to changes in nutrition, clean water, sanitation and basic healthcare — which is why it varies so dramatically between rich and poor countries and is often used as a single proxy for development. DALYs add the crucial dimension of morbidity (illness and disability, not just death), capturing the growing burden of conditions like depression, diabetes and chronic pain that disable without killing. And the maternal mortality ratio is a searching test of whether a health system functions, because safe childbirth requires skilled attendants, emergency surgery and blood supplies. A sophisticated answer selects the indicator that best fits the question rather than defaulting to life expectancy alone.

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The Epidemiological Transition Model (Omran 1971)

Abdel Omran (1971) proposed the epidemiological transition model, which describes how the pattern of disease changes as a country develops economically and undergoes the demographic transition.

graph LR
    S1["Stage 1: Age of<br/>Pestilence & Famine<br/>Infectious disease,<br/>famine, high mortality"] --> S2["Stage 2: Age of<br/>Receding Pandemics<br/>Improved sanitation,<br/>medicine; mortality falls"]
    S2 --> S3["Stage 3: Age of<br/>Degenerative & Man-Made<br/>Diseases<br/>Heart disease, cancer,<br/>stroke dominate"]
    S3 --> S4["Stage 4: Age of<br/>Delayed Degenerative<br/>Diseases<br/>Medical advances extend<br/>life with chronic conditions"]

Stages in Detail

Stage	Name	Dominant Diseases	Life Expectancy	Example
1	Age of Pestilence and Famine	Infectious diseases: plague, cholera, smallpox, tuberculosis; famine	20–40 years	Pre-industrial societies; no modern examples
2	Age of Receding Pandemics	Infectious diseases decline as sanitation, nutrition, and medicine improve	30–50 years	Parts of sub-Saharan Africa (transitioning)
3	Age of Degenerative and Man-Made Diseases	Non-communicable diseases: cardiovascular disease, cancer, stroke, diabetes	50–75 years	UK (mid-20th century), emerging economies
4	Age of Delayed Degenerative Diseases	Same diseases as Stage 3, but onset delayed by medical advances (statins, chemotherapy, screening)	75+ years	UK, Japan, most HICs today

Omran's model parallels the DTM and is best understood alongside it: as a society industrialises (DTM Stage 2 onwards), the same improvements that cut the death rate — sanitation, clean water, nutrition, vaccination, antibiotics — also shift the causes of death away from infection. The diseases that remain are the degenerative conditions of long life (heart disease, cancer, stroke) plus "man-made" diseases of modern lifestyle and environment (obesity, smoking-related cancers, pollution). Omran identified several possible paths through the transition: a "classical/Western" model (slow, as in Europe), an "accelerated" model (faster, as in Japan), and a "delayed/contemporary" model for developing countries where the transition is incomplete and the change is driven heavily by imported medical technology rather than internal development — which is why many LICs face a mixed disease burden.

A Possible Stage 5?

Some scholars have proposed a fifth stage characterised by the re-emergence of infectious diseases (e.g., antibiotic-resistant bacteria, novel pandemics like COVID-19) alongside persistent non-communicable diseases. This concept, sometimes called the Age of Re-emerging Infectious Diseases, reflects:

• The rise of antimicrobial resistance (AMR) — the WHO describes AMR as one of the top 10 global public health threats, and projections (the O'Neill review) warn it could cause millions of deaths a year by 2050 if unaddressed, as the antibiotics that underpinned Stage 2 lose effectiveness
• Emerging and re-emerging infectious diseases — HIV/AIDS, Ebola, SARS, MERS, Zika and COVID-19, many of them zoonotic (jumping from animals to humans)
• Globalisation accelerating the spread of pathogens through international travel and trade — COVID-19 spread worldwide within weeks, a speed impossible in earlier transitions
• Climate and land-use change expanding the range of vectors and increasing human–wildlife contact, raising the risk of spillover

The plausibility of Stage 5 is a strong evaluative point: it suggests Omran's optimistic, one-directional model under-estimated the resilience and adaptability of pathogens and the new risks created by globalisation and environmental change.

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Communicable vs Non-Communicable Diseases

Feature	Communicable Diseases (CDs)	Non-Communicable Diseases (NCDs)
Definition	Diseases caused by pathogens (bacteria, viruses, parasites) that can be transmitted between people or from animals	Diseases not caused by infection and not transmissible between people
Examples	Malaria, tuberculosis, HIV/AIDS, cholera, COVID-19	Cardiovascular disease, cancer, diabetes, COPD, mental illness
Transmission	Direct contact, airborne, waterborne, vector-borne	Not transmitted; caused by genetics, lifestyle, environment
Geographic pattern	More prevalent in LICs (due to poverty, poor sanitation, limited healthcare)	More prevalent in HICs (due to ageing, diet, sedentary lifestyle) but increasing rapidly in LICs/MICs
Prevention	Vaccination, sanitation, mosquito control, hygiene education	Lifestyle changes (diet, exercise, smoking cessation), screening

Key Definition: A vector-borne disease is one transmitted by an organism (vector), typically an insect. Malaria is transmitted by Anopheles mosquitoes; dengue by Aedes mosquitoes; Lyme disease by ticks.

The communicable/non-communicable distinction maps directly onto the development gradient and the epidemiological transition. In the poorest countries (earlier transition stages), the disease burden is dominated by communicable diseases linked to poverty, unsafe water and weak healthcare — a burden that is, in principle, preventable through development. In rich countries (later stages), the burden has shifted to non-communicable diseases of ageing and lifestyle. The complication, increasingly important, is that middle-income countries now face both at once — the unfinished business of infection plus the rising tide of chronic disease from the nutrition transition and ageing — the "double burden" that strains their developing health systems. This is why the simple "infectious = poor, chronic = rich" picture is breaking down, and why the geography of disease is becoming more complex rather than less.

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Environmental Determinants of Health

The relationship between environment and health operates through multiple pathways:

1. Physical Environment

• Water quality — contaminated water causes 485,000 diarrhoeal deaths per year (WHO, 2023); access to clean water is the single most important environmental determinant of health in LICs
• Air quality — outdoor air pollution causes approximately 4.2 million premature deaths per year (WHO); indoor air pollution from solid fuel use causes a further 3.8 million deaths, predominantly in LICs
• Climate — tropical climates support vector-borne diseases; extreme heat causes heat-related illness; climate change is expanding the geographic range of diseases like dengue
• Natural hazards — earthquakes, flooding, and storms cause direct mortality and indirect health impacts through displacement, infrastructure damage, and disease outbreaks

2. Built Environment

• Housing quality — damp, overcrowded housing increases respiratory disease; the UK has approximately 4 million homes with serious health hazards (English Housing Survey)
• Urban planning — access to green spaces associated with better mental health and physical activity; urban heat island effect increases heat-related mortality in cities
• Transport infrastructure — road traffic injuries kill approximately 1.35 million people per year globally (WHO)
• Sanitation infrastructure — approximately 3.6 billion people lack safely managed sanitation (WHO/UNICEF JMP, 2023), the single largest environmental driver of diarrhoeal disease and child mortality in LICs
• Food environment — the local availability and affordability of healthy versus processed food shapes diet-related disease; deprived "food deserts" with abundant fast food but little fresh produce contribute to the social gradient in obesity

3. Social and Economic Environment

• Poverty — the most fundamental determinant of health; poor people are more likely to live in unhealthy environments, have inadequate nutrition, and lack healthcare access
• Education — especially female education; research consistently shows that maternal education is the strongest predictor of child health outcomes
• Employment — unemployment and precarious employment are associated with mental illness, substance abuse, and premature mortality
• Social capital — strong community networks and social support improve health outcomes

Key Definition: The social determinants of health are the conditions in which people are born, grow, live, work, and age. Sir Michael Marmot's landmark research (the Marmot Review, 2010, updated 2020) demonstrated that health inequalities in England follow a "social gradient" — the lower the socio-economic position, the worse the health outcomes, in a continuous gradient (not just rich vs poor).

The development–health relationship

The link between development and health is strong but non-linear and two-way, which is essential for evaluation.

• It is strong: as countries develop, incomes rise, clean water and sanitation spread, healthcare improves, nutrition increases and education (especially of women) expands — so mortality falls and life expectancy rises, exactly as the DTM and epidemiological transition describe. The correlation between GDP per capita and life expectancy is one of the most robust in development (the "Preston curve").
• It is non-linear: the Preston curve is steep at low incomes (a small rise in income buys large health gains where basics are lacking) but flattens at high incomes (extra income buys little extra life expectancy once basic needs are met). This is why the biggest health returns come from lifting the poorest, not enriching the already-rich.
• It is two-way: poor health causes underdevelopment (a malarial or HIV-stricken workforce is less productive; sick children learn less), as well as resulting from it — a vicious or virtuous circle.
• It is modifiable by governance: some places achieve far better health than their income predicts. The Indian state of Kerala and Cuba attain life expectancies close to HIC levels at a fraction of the income, through strong public health, education and near-universal primary care — proving that political choices, not just wealth, shape health.

This last point is the key evaluative move: development enables good health, but how a society distributes income and invests in public health determines whether that potential is realised.

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Case Study: HIV/AIDS and Development in Southern Africa

Southern Africa shows the development–health relationship working in reverse — a disease so severe it set back demographic and economic progress:

• At the epidemic's peak (late 1990s–2000s), several southern African countries had adult HIV prevalence above 20–25% (Eswatini, Botswana, Lesotho), the highest in the world
• Life expectancy in Botswana fell from around 64 (1990) to below 50 (2000s) before antiretroviral therapy reversed the decline — a dramatic demonstration that the DTM/epidemiological transition can go backwards
• The disease struck working-age adults hardest, orphaning millions of children, stripping economies of skilled labour, and overwhelming health systems
• The turnaround came through development and global governance: the rollout of antiretroviral therapy (ART), funded heavily by PEPFAR and the Global Fund, has restored life expectancy and turned HIV into a manageable chronic condition — a major public-health success, though prevention and stigma challenges remain

This case is invaluable because it shows that health and development are mutually dependent, that the epidemiological transition is not guaranteed to be one-directional, and that global action (the subject of the next lesson) can reverse a health catastrophe.

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Case Study: Air Pollution and Health in the UK