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Understanding the difference between health and disease is the starting point for this entire topic. You need to know the World Health Organisation (WHO) definition of health, the distinction between communicable and non-communicable diseases, and how different factors affect the likelihood of developing disease.
The World Health Organisation (WHO) defines health as:
"A state of complete physical, mental and social well-being, and not merely the absence of disease or infirmity."
This definition is important because it goes beyond just "not being ill." A person who is physically fit but suffering from severe anxiety, or someone who is physically well but socially isolated, would not be considered healthy under this definition.
| Dimension | Meaning | Examples of poor health |
|---|---|---|
| Physical | The body is free from disease and functioning well | Broken bone, cancer, flu |
| Mental | The mind is functioning well; emotional well-being | Depression, anxiety, stress |
| Social | Ability to interact with others and maintain relationships | Isolation, bullying, lack of community |
Exam tip: If asked to define health, you must include all three dimensions — physical, mental, and social. Simply writing "not being ill" will not gain full marks.
Diseases are broadly divided into two categories: communicable and non-communicable.
| Feature | Communicable | Non-communicable |
|---|---|---|
| Caused by pathogen? | Yes | No |
| Can spread between organisms? | Yes | No |
| Examples | Measles, TB, malaria | Cancer, diabetes, CVD |
| Prevention focus | Hygiene, vaccination, vector control | Lifestyle changes, screening |
A risk factor is something that increases the likelihood of developing a disease. Risk factors can be:
| Risk factor | Associated diseases |
|---|---|
| Smoking | Lung cancer, cardiovascular disease, chronic obstructive pulmonary disease (COPD) |
| Obesity / poor diet | Type 2 diabetes, cardiovascular disease, some cancers |
| Excessive alcohol consumption | Liver disease (cirrhosis), liver cancer, brain damage |
| Lack of exercise | Cardiovascular disease, type 2 diabetes, obesity |
| Genetic predisposition | Some cancers (e.g. BRCA gene and breast cancer), cystic fibrosis |
| Ionising radiation | Cancer (mutations in DNA) |
| Exposure to carcinogens | Cancer (e.g. asbestos → mesothelioma, UV light → skin cancer) |
Tobacco smoke contains over 4,000 chemicals, including:
Smoking during pregnancy can lead to:
This is a critical concept that examiners love to test.
Correlation does not automatically prove causation.
Scientists found a correlation between ice cream sales and drowning rates — both increase in summer. Does ice cream cause drowning? Of course not. The confounding variable is hot weather, which increases both ice cream sales and swimming activity.
Exam tip: If a question gives you a graph showing a correlation and asks "Does this prove that X causes Y?", the answer is almost always no. Explain that correlation does not prove causation and suggest a possible confounding variable.
Diseases do not exist in isolation. Having one disease can make a person more susceptible to developing another.
| Situation | Explanation |
|---|---|
| HIV and communicable diseases | HIV destroys T helper lymphocytes (a type of white blood cell), weakening the immune system. This makes the person much more susceptible to communicable diseases such as TB and pneumonia. |
| Poor diet and communicable diseases | Malnutrition weakens the immune system because the body lacks the nutrients needed to produce white blood cells and antibodies. This increases vulnerability to infections. |
| Immune system deficiency and infections | People with defective immune systems (e.g. due to genetic conditions or chemotherapy) are at greater risk of communicable diseases. |
| Mental health and physical disease | Depression and chronic stress can weaken the immune system (through raised cortisol levels), making infections more likely. Conversely, chronic physical illness can cause or worsen mental health conditions. |
| Viruses and cancer | Some viruses increase the risk of certain cancers. For example, HPV (human papillomavirus) is linked to cervical cancer. Hepatitis B and C viruses increase the risk of liver cancer. |
Exam tip: Be prepared to explain how having one type of disease can increase the risk of developing another type. The most common example in exams is HIV weakening the immune system and leading to increased risk of communicable diseases.
A study followed 10,000 adults for 20 years, recording lifestyle and cardiovascular disease (CVD) outcomes.
| Group | Smokers with CVD | Non-smokers with CVD |
|---|---|---|
| Men aged 40–60 | 28% | 9% |
| Women aged 40–60 | 22% | 7% |
Interpreting the data:
Common mistake: Writing "smoking causes CVD because 28% of smokers had it" ignores confounding variables (age, diet, exercise) and does not address the need for a mechanism. For full marks, always reference controlled comparison, sample size, and biological mechanism.
| Feature | Communicable | Non-communicable |
|---|---|---|
| Typical cause | Pathogen (bacterium, virus, fungus, protist) | Lifestyle, genetics, environment |
| Transmissible? | Yes — direct contact, droplet, vector, food, water | No |
| Onset | Often acute (hours to days) | Often chronic (months to years) |
| Example in the UK | Influenza, tuberculosis | Type 2 diabetes, cardiovascular disease |
| Key prevention tool | Vaccine, hygiene, vector control | Lifestyle change, screening, legislation |
| Immune response involved? | Yes — antibody and memory cell formation | Not directly |
graph TD
A["Risk factor - smoking, poor diet, alcohol"] --> B["Cellular or systemic damage"]
B --> C["Raised blood pressure / DNA mutation / cirrhosis"]
C --> D["Non-communicable disease develops"]
E["Pathogen exposure"] --> F["Pathogen evades barriers"]
F --> G["Immune response activated"]
G --> H["Communicable disease symptoms"]
Question: "A study reports a correlation between long hours sitting at a desk and increased risk of type 2 diabetes. Explain whether this proves that sitting causes diabetes. (4 marks)"
Model answer:
Mistake 1: Defining health as "not being ill." The WHO definition requires physical, mental and social well-being.
Mistake 2: Treating risk factor and cause as synonyms. A risk factor increases probability; a cause is a demonstrated mechanism. Smoking is a risk factor for lung cancer and a contributory cause because tar in tobacco smoke mutates DNA.
Mistake 3: Forgetting that some non-communicable diseases have genetic components (e.g. BRCA mutations and breast cancer) which are not lifestyle choices.
Grade 3–4 response: "Diseases are things that make you ill. Some spread like flu. Others like cancer do not spread. Smoking can cause cancer."
Grade 6–7 response: "A communicable disease is caused by a pathogen such as a virus or bacterium and can be transmitted between people. A non-communicable disease is not caused by a pathogen and cannot spread. A risk factor such as smoking raises the likelihood of developing non-communicable disease."
Grade 8–9 response: "The WHO defines health as complete physical, mental and social well-being. A communicable disease results from infection by a pathogen and triggers an immune response, often producing antibodies and memory cells that give immunity on re-exposure (potentially assisted by a vaccine). A non-communicable disease arises from risk factors including lifestyle, genetics and environment — for example, tar from tobacco smoke mutates lung epithelial DNA, leading to uncontrolled division. Correlation between a risk factor and a disease does not prove causation: controlled studies, biological mechanisms and peer review are required."
Edexcel alignment: This content is aligned with Edexcel GCSE Biology (1BI0) specification Topic 6 Health, disease and the development of medicines — specifically 6.1 Health and disease, 6.8 Non-communicable disease and risk factors. Assessed on Paper 2.
| Trend | Consequence for students to understand |
|---|---|
| Ageing populations in the UK | Increased burden of non-communicable disease such as cardiovascular disease and type 2 diabetes |
| Rising obesity rates | More cases linked to the obesity-related risk factor cluster |
| Improved sanitation | Historical decline in communicable disease mortality |
| Antimicrobial resistance | Resurgent threat from communicable diseases once treatable |
| Vaccination programmes | Elimination of smallpox, near-elimination of polio; reliance on continued uptake |
Why this matters: GCSE questions increasingly ask candidates to apply their knowledge to public-health scenarios. Quoting a specific risk factor and explaining how it contributes to a particular non-communicable disease is exactly the analytical move examiners reward. Students who can confidently distinguish pathogen-driven illness from lifestyle-driven illness will gain credit even when the scenario is unfamiliar.
Callout: Remember that a person can have more than one disease at the same time. HIV (a communicable disease) suppresses the immune response, leaving the body unable to produce sufficient antibodies against other pathogens. This interaction is tested every year.
Callout: Obesity is a risk factor, not a disease in itself. It raises the probability of cardiovascular disease, type 2 diabetes and certain cancers. Present it as a risk factor in exam answers.
Callout: When a question mentions a vaccine in the context of non-communicable disease, check carefully — some vaccines reduce cancer risk (e.g. HPV and cervical cancer) because the cancer is triggered by a viral pathogen.