️ Causes of Non-infectious Disease — Genetic, Environmental, Nutritional, Cancer
In 1900 the leading killers in Australia were all infectious — pneumonia, tuberculosis, diarrhoeal disease. Today the top five are coronary heart disease, dementia, stroke, lung cancer and COPD — none contagious. This lesson sets up IQ2: the four categories of non-infectious disease, why a risk factor is not a cause, and why these diseases now dominate.
Practise this lesson
Four printable worksheets that build from the foundations up to exam-style questions — start at whatever level suits you.
Epidemiology measures the distribution and determinants of disease in populations
In 1900, the leading causes of death in Australia were pneumonia, tuberculosis, and diarrhoeal diseases — all infectious. Today, the top five causes of death are coronary heart disease, dementia/Alzheimer's, cerebrovascular disease, chronic lower respiratory disease, and lung cancer — none of which are contagious.
This dramatic shift happened within a single century. Antibiotics, vaccines, sanitation, and improved nutrition dramatically reduced infectious disease mortality. Meanwhile, people are living long enough for non-infectious diseases — which often take decades to develop — to become the dominant killers.
Before reading on, answer both questions:
Q1: You have 60 seconds. Write down as many non-infectious diseases as you can think of. Try to group them — which seem to share similar causes?
Q2: Some people with no family history of heart disease develop it young. Others with every known risk factor never do. What does this suggest about how risk factors actually work?
Know
- The definition of non-infectious disease and how it differs from infectious disease
- The four categories of non-infectious disease: genetic, environmental, nutritional, cancer
- At least two examples of each category
- Why non-infectious diseases cause more deaths globally than infectious diseases
Understand
- Why a risk factor is not the same as a cause
- Why most non-infectious diseases are multifactorial
- How genetic predisposition and environmental exposure interact
- Why the shift from infectious to non-infectious disease as a leading killer reflects social progress
Can Do
- Classify any given disease into the correct non-infectious category
- Distinguish between a risk factor and a direct cause
- Explain why non-infectious diseases dominate mortality statistics using Australian data
- Apply the concept of multifactorial disease to a specific example
Core Content
Transmission is the key — not severity, not treatability, not genetic involvement
The defining distinction between infectious and non-infectious disease is not how serious it is, not whether genetics are involved, and not whether it can be treated — it is whether the disease can be transmitted from one individual to another via a pathogen.
Causes of non-infectious disease: genetic, environmental, lifestyle and nutritional factors
Classification flowchart for identifying disease type
An infectious disease is caused by a pathogen — a bacterium, virus, fungus, or parasite — that can be transmitted between hosts through direct contact, airborne droplets, water, food, vectors, or other routes. The pathogen invades the host, replicates, and causes damage. Examples: tuberculosis, COVID-19, malaria, HIV/AIDS, hepatitis B.
A non-infectious disease cannot be transmitted from person to person via a pathogen. It arises from internal factors (genetic mutations, cellular malfunction) or interactions between an individual's biology and their environment or nutrition. It cannot be 'caught.' However — and this is important — some non-infectious diseases have infectious triggers. HPV infection can lead to cervical cancer (a non-infectious disease). Helicobacter pylori infection can lead to gastric cancer. In these cases, the pathogen is a risk factor, but the resulting cancer is non-infectious: you cannot 'catch' cancer from a cancer patient.
| Feature | Infectious Disease | Non-infectious Disease |
|---|---|---|
| Cause | Pathogen (bacterium, virus, fungus, parasite) | Genetic, environmental, nutritional, or cellular factors |
| Transmissible? | Yes — can spread between individuals | No — cannot be transmitted via pathogen |
| Prevention | Vaccines, hygiene, vector control, antibiotics | Lifestyle modification, genetic screening, avoiding exposures |
| Timeline | Often acute — rapid onset and resolution | Often chronic — develops over months to decades |
| Treatment approach | Target and eliminate pathogen | Manage symptoms, slow progression, modify risk factors |
| Australian top killer? | Not in the top 5 causes of death | Yes — coronary heart disease, dementia, cancer are #1–3 |
What to write in your book
- Infectious = caused by a transmissible pathogen; non-infectious = cannot be caught.
- Non-infectious ≠ non-genetic — CF and Huntington's are genetic AND non-infectious.
- Some non-infectious diseases have infectious triggers (HPV → cervical cancer; H. pylori → gastric cancer).
- Non-infectious diseases are usually chronic and dominate Australia's top causes of death.
A genetic disease such as cystic fibrosis is classified as infectious because it is passed down from parents.
Non-infectious diseases are caused by genetic, environmental, nutritional, and lifestyle factors rather than pathogens.
Cancer is a non-infectious disease caused by uncontrolled cell division that cannot be influenced by environmental factors.
Every non-infectious disease in L07–L10 fits one of these categories — or spans several
The NESA syllabus organises non-infectious diseases into four categories based on their primary cause. These categories are not mutually exclusive — most real diseases involve multiple categories interacting — but they provide a useful framework for classifying and studying mechanisms.
Genetic Diseases
Caused by mutations in one or more genes that produce altered or non-functional proteins. May be inherited or arise spontaneously. Present from birth, though symptoms may appear at any age.
- Cystic fibrosis (CFTR gene mutation)
- Huntington's disease (CAG repeat expansion)
- PKU (phenylalanine hydroxylase mutation)
- Type 1 diabetes (autoimmune, genetic predisposition)
- BRCA1/2 mutations (breast/ovarian cancer risk)
Environmental Diseases
Caused or contributed to by exposure to harmful agents in the physical or social environment (chemical, physical, or biological). Often dose-dependent.
- Lung cancer (tobacco smoke carcinogens)
- Mesothelioma (asbestos fibre inhalation)
- Melanoma (UV radiation → DNA damage)
- COPD (cigarette smoke, air pollution)
- Lead poisoning (environmental lead exposure)
Nutritional Diseases
Caused by deficiency or excess of specific nutrients. Deficiency deprives cells of essential components; excess overwhelms regulatory mechanisms or deposits toxic byproducts.
- Vitamin D deficiency (rickets, osteoporosis)
- Vitamin C deficiency (scurvy)
- Iron deficiency anaemia
- Iodine deficiency (goitre, cretinism)
- Type 2 diabetes & CVD (excess refined sugars/fats)
Cancer
Characterised by uncontrolled cell division due to disruption of cell cycle regulation. Can have genetic, environmental, nutritional, or infectious triggers — treated as distinct because the mechanism is unique.
- Skin cancer / melanoma
- Lung cancer
- Bowel (colorectal) cancer
- Breast cancer
- Leukaemia (blood cell cancer)
What to write in your book
- Genetic: gene mutation → altered protein → disease (CF, Huntington's, PKU).
- Environmental: exposure to a harmful agent → disease (lung cancer, mesothelioma, melanoma).
- Nutritional: deficiency or excess of nutrients (scurvy, rickets, T2D).
- Cancer: uncontrolled cell division — its own category, often with genetic/environmental triggers.
Melanoma is a skin cancer caused mainly by UV radiation. How is it best classified?
Not because they got worse — because infectious diseases got much better controlled
Non-infectious diseases do not cause more deaths because they became more dangerous — they cause more deaths because medical advances dramatically reduced infectious disease mortality over the 20th century, revealing non-infectious diseases as the dominant remaining killers as populations age.
The global burden of disease
According to the WHO, non-communicable diseases (NCDs) account for approximately 74% of all deaths globally — about 41 million people per year. The four main categories are cardiovascular diseases (17.9 million/year), cancers (9.3 million), chronic respiratory diseases (4.1 million), and diabetes (2.0 million). Infectious diseases account for a much smaller proportion of global mortality — though they remain dominant in low-income countries where access to NCD treatment is limited.
Why Australia reflects this pattern
The AIHW reports that the top causes of death in Australia are overwhelmingly non-infectious. Coronary heart disease alone accounts for approximately 10% of all Australian deaths annually. Effective vaccination, antibiotics, clean water, and improved nutrition since 1900 dramatically reduced deaths from pneumonia, tuberculosis, diarrhoeal disease, and childhood infections — leaving non-infectious diseases as the dominant cause of mortality in an ageing, well-nourished population.
Key reasons for NID dominance
- Ageing populations: Most non-infectious diseases take decades to develop. As life expectancy increased (Australian average ~83 years), more people survive long enough for these diseases to manifest.
- Infectious disease control: Vaccines, antibiotics, and sanitation dramatically reduced premature death from infectious disease. People who would have died of pneumonia at 50 in 1900 now live to 80 and die of cardiovascular disease.
- Lifestyle changes: Sedentary behaviour, processed food, obesity, and smoking — all factors in non-infectious disease — increased substantially in industrialised nations.
- Better diagnosis: Improved diagnostic technology means non-infectious diseases are more reliably identified and attributed as causes of death.
What to write in your book
- Epidemiological transition = 20th-century shift from infectious to non-infectious disease as the leading killer.
- WHO: NCDs ≈ 74% of global deaths (CVD, cancer, chronic respiratory, diabetes).
- AIHW: coronary heart disease ≈ 10% of all Australian deaths; top 5 all non-infectious.
- Drivers: ageing populations, infectious-disease control, lifestyle changes, better diagnosis.
The 20th-century shift from infectious to non-infectious disease as the leading cause of death is called the epidemiological _____.
A risk factor increases probability — it does not guarantee disease, and its absence does not guarantee health
Most non-infectious diseases are not caused by a single factor. They are multifactorial — caused by the interaction of genetic predisposition, environmental exposures, nutritional status, and lifestyle behaviours over time. This is why two people with identical risk factors can have different outcomes, and why someone with no apparent risk factors can still develop a disease.
What is a risk factor?
A risk factor is any characteristic, behaviour, or exposure that increases the statistical probability of developing a disease. Risk factors are identified through epidemiological studies — they show association, not causation. A risk factor increases the likelihood of disease without making it inevitable. Risk factors for cardiovascular disease include family history, smoking, high-fat diet, physical inactivity, hypertension, obesity, age, male sex, and Type 2 diabetes. No single factor guarantees heart disease — but someone with multiple factors simultaneously has a dramatically elevated risk.
Why multifactorial disease is the norm
Very few non-infectious diseases are purely single-factor. Even cystic fibrosis — considered a 'pure' genetic disease — has variable severity influenced by environmental factors (respiratory infections, air quality) and nutritional factors (enzyme supplementation, diet). Type 2 diabetes requires both genetic susceptibility (some ethnic groups have 3–4× higher baseline risk) AND environmental/nutritional triggers (obesity, sedentary behaviour, high sugar diet). Remove either component and the disease is far less likely.
The interaction between factors also matters. A BRCA1 mutation significantly increases breast cancer risk — but the risk is not 100%. Lifestyle factors modify the expressed risk. Genetic predisposition sets the background probability; environmental and nutritional factors shift it up or down.
| Disease | Genetic factors | Environmental factors | Nutritional factors | Category |
|---|---|---|---|---|
| Type 2 diabetes | Family history, ethnicity | Physical inactivity, sedentary work | High sugar/fat diet, obesity | Nutritional (primary); multifactorial |
| Lung cancer | Genetic susceptibility to carcinogens | Tobacco smoke, radon, asbestos | Low antioxidant diet (minor) | Environmental (primary); multifactorial |
| Cystic fibrosis | CFTR gene mutation (both alleles) | Respiratory infections worsen prognosis | Malabsorption → nutritional deficiency | Genetic (primary) |
| Cardiovascular disease | Family history, APOE alleles | Smoking, air pollution, stress | Saturated fat, salt, refined carbohydrate | Multifactorial |
| Melanoma | Fair skin, CDKN2A mutations | UV radiation (primary trigger) | Minor nutritional factors | Environmental/Cancer; multifactorial |
What to write in your book
- Risk factor = increases probability of disease (association, not causation); does not guarantee it.
- Most non-infectious diseases are multifactorial: genetic + environmental + nutritional + lifestyle interact.
- Genetic predisposition sets the baseline; environment/nutrition shift the risk up or down.
- Identical risk factors can give different outcomes; no risk factors ≠ guaranteed health.
A risk factor is best described as something that:
Classify Each Disease
For each, classify into the most appropriate non-infectious category AND state whether it is infectious or non-infectious. Justify in one sentence; if multifactorial, name the primary category and contributing factors.
- Cystic fibrosis — a CFTR gene mutation produces a dysfunctional chloride channel, leading to thick mucus in lungs and digestive tract.
- Mesothelioma — a rare cancer of the lung lining, strongly associated with past asbestos exposure.
- Scurvy — caused by insufficient vitamin C, resulting in impaired collagen synthesis, bleeding gums, poor wound healing.
- Type 2 diabetes — cells become resistant to insulin, linked to obesity, inactivity, high-sugar diets, genetic predisposition, ethnicity.
- Cervical cancer — caused by persistent HPV infection, which causes mutations in cervical epithelial cells that disrupt cell cycle control.
Risk Factors and Multifactorial Disease
Answer using precise biological and epidemiological language.
- Two siblings are raised in the same household with the same diet, both non-smokers with similar activity. Sibling A develops coronary heart disease at 52; Sibling B (same age) does not. Using multifactorial disease and risk factors, explain why this is possible.
- Australia's leading cause of death is coronary heart disease. Using AIHW data and the epidemiological transition, explain why this is the case and why tuberculosis — a leading killer in 1900 — now causes very few Australian deaths. What does this tell you about the relationship between social/medical progress and patterns of disease?
The AIHW publishes annual burden of disease data for Australia. The 2022 report shows the leading causes of death are: (1) Coronary heart disease — approximately 10% of all deaths; (2) Dementia including Alzheimer's disease; (3) Cerebrovascular disease (stroke); (4) Lung cancer; (5) Chronic lower respiratory diseases (including COPD). All five are non-infectious diseases.
The same data show that total years of healthy life lost (Disability Adjusted Life Years, DALYs) is dominated by non-infectious conditions: mental health disorders, musculoskeletal conditions, cardiovascular disease, and cancer collectively account for over 60% of all DALYs. Infectious diseases — including COVID-19 in the most recent data — account for a much smaller proportion.
Importantly, Indigenous Australians experience a significantly higher burden of non-infectious disease — cardiovascular disease rates 1.7× higher, diabetes rates 3× higher — reflecting the interaction of genetic, socioeconomic, nutritional, and environmental risk factors. This epidemiological pattern will be relevant when you study epidemiology in L12–L14.
Four Categories
- Genetic: gene mutation → altered protein → disease
- Environmental: exposure to harmful agent → disease
- Nutritional: deficiency or excess of nutrients → disease
- Cancer: uncontrolled cell division (genetic/environmental triggers)
Infectious vs Non-infectious
- Infectious: caused by pathogen; transmissible
- Non-infectious: no pathogen; not transmissible
- Key: non-infectious ≠ non-genetic
- Some NID have infectious triggers (HPV → cervical cancer)
Risk Factors
- Increase probability — do not guarantee disease
- Most NID are multifactorial
- Genetic + environmental + nutritional factors interact
- Australian data: AIHW; global data: WHO
Why NID Kills More
- Ageing populations — NID take decades to develop
- Infectious disease controlled by vaccines/antibiotics
- Lifestyle changes (obesity, inactivity, processed food)
- Better diagnosis = more accurate attribution
A fresh set drawn from this lesson's question bank — feedback shown immediately. +5 XP per correct · +25 XP all correct
Pick your answer, then rate your confidence — that tells the system what to drill next.
ApplyBand 3–4(4 marks) 1. Identify and classify two non-infectious diseases from different categories, providing the primary cause and one specific example of how that cause leads to disease at the cellular or molecular level.
AnalyseBand 4–5(5 marks) 2. Explain why non-infectious diseases now cause more deaths in Australia than infectious diseases. Refer to specific AIHW data, the epidemiological transition, and at least two factors that contributed to the shift.
EvaluateBand 5–6(5 marks) 3. Type 2 diabetes is often described as a 'lifestyle disease.' Evaluate the accuracy of this description by analysing the genetic, environmental, nutritional, and socioeconomic factors that contribute. Conclude by explaining whether the label is useful, misleading, or both.
Show all answers
Multiple choice
MC answers and full explanations are shown inline as you complete each question. Use the retry button to attempt a fresh set from the lesson bank.
Activity 1 — Classify Each Disease
1. Cystic fibrosis: Non-infectious. Genetic — a mutation in both copies of the CFTR gene produces a dysfunctional chloride ion channel; Cl⁻ cannot be transported normally, leading to thick dehydrated mucus in airways and the digestive system. Autosomal recessive (needs both alleles).
2. Mesothelioma: Non-infectious. Both environmental and cancer — inhaled asbestos fibres lodge in the pleural lining, causing chronic inflammation and DNA damage to mesothelial cells over decades; the outcome is uncontrolled cell division. Best classified as cancer with a primary environmental cause. You cannot 'catch' it from a patient.
3. Scurvy: Non-infectious. Nutritional — caused by insufficient dietary vitamin C, a required cofactor for prolyl hydroxylase (collagen synthesis). Without it, collagen is structurally defective → weakened blood vessel walls → bleeding gums, petechiae, poor wound healing.
4. Type 2 diabetes: Non-infectious. Primarily nutritional but multifactorial — excess refined sugar/saturated fat plus inactivity → obesity and insulin resistance; genetic predisposition (some ethnic groups 3–4× higher baseline risk) and environmental factors also significant. Sits at the intersection of all four categories.
5. Cervical cancer: Non-infectious (the cancer itself); category = cancer. HPV is an infectious organism but the cancer is not — HPV is a risk factor/trigger that causes mutations (e.g. in CDKN2A) disrupting cell cycle control in cervical epithelial cells. Only the HPV virus is transmissible — a key example of an infectious trigger for a non-infectious disease.
Activity 2 — Risk Factors and Multifactorial Disease
1. Same household, different outcomes: Risk factors are probabilistic. Even with identical household environments, the siblings have different genomes — variation in lipid metabolism (e.g. APOE alleles), blood pressure regulation, inflammatory response — giving different baseline cardiovascular risk. Subtle behavioural differences, epigenetic variation, and random biological events (e.g. spontaneous arterial-wall mutations) also contribute. This is the core of multifactorial disease: identical exposures do not produce identical outcomes because genetic and individual variation modifies risk. A risk factor is a population-level predictor, not an individual determinant.
2. Epidemiological transition: CHD is now Australia's leading cause of death because (i) vaccines, antibiotics (1940s), sanitation and better nutrition dramatically reduced infectious-disease mortality, so people who would have died of pneumonia/TB at younger ages now survive into their 60s–80s; (ii) non-infectious diseases like CHD take decades to develop and an ageing population (median age ~25 in 1900 → ~38 today) means more people live long enough to develop them; (iii) industrialised lifestyle factors (sedentary work, processed food, smoking) increased population NID risk. TB declined due to BCG/childhood vaccination, antibiotics, and sanitation. Patterns of disease are shaped by the interaction of social progress, medical technology, environmental change and demographics — not biology alone.
Short Answer Model Answers
SA1 (4 marks): Disease 1 — Cystic fibrosis (genetic): autosomal recessive CFTR mutation (commonly F508del) causes the CFTR chloride channel to misfold and be degraded before reaching the membrane; without functional Cl⁻ channels, chloride and water cannot be secreted into airways → thick mucus → chronic infection and malabsorption [2]. Disease 2 — Melanoma (cancer with environmental cause): UV radiation causes thymine dimers in skin-cell DNA, disrupting tumour suppressors (e.g. CDKN2A/p16) and proto-oncogenes (e.g. BRAF); accumulated mutations disrupt cell-cycle checkpoints → uncontrolled melanocyte division → malignant melanoma [2].
SA2 (5 marks): AIHW: CHD is the leading cause of death (~10% of deaths), followed by dementia, cerebrovascular disease, lung cancer, COPD — all non-infectious; infectious disease is not in the top five [1]. Epidemiological transition: the 20th-century shift from infectious to non-infectious disease as the dominant cause of mortality as infectious-disease deaths fell [1]. Factor 1 — infectious-disease control: antibiotics, vaccination, sanitation and better nutrition reduced deaths from TB, pneumonia and childhood infections, so people survive to develop NID [1.5]. Factor 2 — ageing populations: life expectancy rose from ~55 (1900) to ~83, so far more Australians reach the ages at which CHD, dementia and cancer manifest [1.5].
SA3 (5 marks): Genetic: strong heritable component — first-degree relatives have 2–3× risk; some ethnic groups (Indigenous Australians, South Asian, Pacific Islander) have higher genetic susceptibility — a baseline that cannot be changed by lifestyle [1]. Environmental: physical inactivity and sedentary work, strongly shaped by socioeconomic conditions (access to safe exercise spaces) [1]. Nutritional: chronic excess refined carbohydrate/saturated fat → hyperinsulinaemia, beta-cell exhaustion, insulin resistance; central obesity → inflammation impairing insulin signalling [1]. Socioeconomic: T2D is more prevalent in lower-income, regional and Indigenous populations with less access to fresh produce and preventive healthcare, and higher financial stress [1]. Evaluation: the 'lifestyle disease' label is partially accurate (lifestyle factors are important modifiable risks and the basis of treatment) but misleading because it implies the disease is purely personal choice, ignoring genetic predisposition and socioeconomic determinants, and it can drive stigma. Most accurate: a multifactorial non-infectious disease in which lifestyle factors are important but not solely determinative [1].
Five timed questions on disease categories, risk factors and the epidemiological transition. Beat the boss to bank a tier — gold (perfect + fast), silver (80%+), or bronze (cleared).
⚔ Enter the arenaScale the platforms using your knowledge of causes of non-infectious disease. Pool: lessons 1–6.
Take on the boss-battle arena for this lesson — rapid-fire questions on disease classification and risk factors.
Return to your Think First responses at the start of the lesson.
- Q1 — your disease list: Can you now classify every disease you listed into one of the four categories? Are any multifactorial? Were any actually infectious that you initially listed as non-infectious?
- Q2 — risk factors: State precisely, using the terminology: risk factor, multifactorial disease, genetic predisposition, environmental exposure.
- Write one sentence explaining the epidemiological transition — why the shift to non-infectious disease as the leading killer reflects social and medical progress.