Non-Communicable Diseases and Risk Factors

Health is the state of physical and mental well-being — not just the absence of disease. A person can be free of infection yet still be unhealthy through poor mental health, stress, or a difficult life situation.

Disease is a major cause of ill health, and AQA splits it into two types:

• Communicable (infectious) disease — caused by a pathogen (a microorganism such as a bacterium, virus, fungus or protist) and can spread from one organism to another. Examples: measles, HIV, malaria.
• Non-communicable disease — cannot be passed between people. It usually develops slowly and is often linked to lifestyle or genetics. Examples: cardiovascular disease, type 2 diabetes, most cancers.

Health = physical and mental well-being. A disease is communicable if a pathogen can spread it; non-communicable if it cannot be caught.

Other factors — diet, stress and life situations — also affect both physical and mental health, even when no pathogen is involved. This is why "health" is broader than "not being infected".

Diseases do not act in isolation — one condition can make another more likely. AQA names four specific interactions you must be able to describe:

Starting condition	Leads to	Why
Defect in the immune system	More communicable (infectious) diseases	A weakened immune system cannot fight off pathogens effectively
Viruses living inside cells	Some cancers	The virus can be the trigger that makes cells divide uncontrollably
Immune reaction to a pathogen	Allergies such as skin rashes and asthma	The immune response becomes oversensitive
Severe physical ill health	Depression and other mental illness	Long-term illness affects mood, independence and quality of life

Notice the direction of cause runs both ways across the body: a physical problem (immune defect) can cause an infectious problem, and a physical illness can cause a mental illness. This is exactly why health is defined as physical and mental well-being.

Cancer is covered in its own lesson — here it appears only as an example of a disease that another condition (a virus) can trigger.

A risk factor is anything linked to an increased rate (incidence) of a disease. AQA groups them into two types:

• Aspects of lifestyle — e.g. diet, smoking, alcohol, level of exercise.
• Substances in the body or environment — e.g. carcinogens, including ionising radiation.

A risk factor raising the rate of a disease does not automatically mean it causes the disease. AQA distinguishes two situations:

• A correlation — two things change together, but a third factor or chance might explain the link.
• A proven causal mechanism — scientists have shown how the factor biologically produces the disease.

A causal mechanism has been demonstrated for some risk factors but not all. Where the biological pathway is known, the link is more than a correlation.

Many non-communicable diseases arise from the interaction of several factors at once — for example, cardiovascular disease is influenced by diet, exercise, smoking and inherited genes together, not any single cause.

The table below lists the causal links named in section 4.2.2.6, with the mechanism for each. These are cases where the biological pathway — not just a correlation — has been established.

Risk factor	Disease(s) it raises	Mechanism
Diet (high fat / salt / sugar)	Cardiovascular disease, obesity	Fatty deposits narrow coronary arteries; excess energy is stored as fat
Lack of exercise	Cardiovascular disease, obesity	Less energy used, so more is stored; heart muscle stays weaker
Smoking	Cardiovascular disease, lung disease, lung cancer	Chemicals damage artery and airway linings; carcinogens in tar trigger cancer
Obesity	Type 2 diabetes	Body cells stop responding properly to insulin, so blood glucose stays high
Alcohol	Liver disease (cirrhosis), reduced brain function	The liver is damaged breaking down alcohol; alcohol is toxic to brain cells
Smoking and alcohol in pregnancy	Harm to the unborn baby	Substances cross the placenta — e.g. low birth weight, premature birth
Carcinogens, incl. ionising radiation	Cancer	They damage DNA, causing uncontrolled cell division

(Extra context — not required by AQA 8461: the carcinogen in tobacco tar most often discussed in research is benzo[a]pyrene, but AQA only needs "carcinogens in cigarette smoke".)

A study follows two groups of 1000 adults for ten years and records how many develop lung disease:

Group	People studied	Developed lung disease
Smokers	1000	90
Non-smokers	1000	15

Step 1 — find the rate (incidence) in each group.

• Smokers: $\frac{90}{1000}=0.09=9\%$
• Non-smokers: $\frac{15}{1000}=0.015=1.5\%$

Step 2 — find the relative risk (how many times more likely):

$\text{relative risk}=\frac{0.09}{0.015}=6$

Smokers in this study were 6 times more likely to develop lung disease than non-smokers.

Step 3 — find the absolute difference: $90-15=75$ extra cases per 1000 people.

Quote the actual figures from the data ("6 times more likely", "75 extra cases per 1000") rather than vague phrases like "a lot more". Marks come from the numbers you read off, not adjectives.

A second survey of 2000 people records obesity and type 2 diabetes:

Group	People studied	Developed type 2 diabetes
Obese	800	200
Not obese	1200	60

• Incidence in obese group: $\frac{200}{800}=25\%$
• Incidence in non-obese group: $\frac{60}{1200}=5\%$
• Relative risk: $\frac{0.25}{0.05}=5$ — obese people were 5 times more likely to develop the disease.

There is a clear correlation. But a correlation alone does not prove obesity causes type 2 diabetes, because:

• A third factor could explain both — e.g. a high-sugar diet might independently raise weight and raise diabetes risk.
• The link could be reversed or coincidental in a single small sample.

Obesity is an accepted cause of type 2 diabetes — but only because separate research established the mechanism (cells stop responding to insulin), not because of the correlation by itself.

A correlation shows two variables change together. It becomes a cause only when a biological mechanism is demonstrated. Scatter diagrams show correlation; they cannot prove cause on their own.

Non-communicable diseases carry costs at every level. AQA wants you to discuss both the human cost (illness, disability, shorter life, strain on families and mental health) and the financial cost (treatment, lost working days, the burden on health services, and reduced income for families and the wider economy) — locally, nationally and globally.

1. Confusing "communicable" and "non-communicable"

Communicable disease is spread by a pathogen; non-communicable cannot be caught. A heart attack is non-communicable; measles is communicable.

2. Saying a correlation "proves" a cause

A correlation only shows two variables change together. State that a mechanism must be shown before claiming cause, and mention that a third factor could explain the link.

3. Defining health as only physical

Health is physical and mental well-being. An answer that ignores mental health is incomplete.

4. Giving vague data answers

Read exact figures off the table or graph — "6 times more likely", "25% versus 5%" — instead of writing "more" or "a lot higher".

5. Naming a risk factor without the mechanism

For higher marks, link the factor to how it causes the disease — e.g. smoking → carcinogens in tar damage DNA → lung cancer; obesity → cells stop responding to insulin → type 2 diabetes.