5.5 Non-communicable disease — Edexcel GCSE Biology revision notes

5.23–5.24The effect of lifestyle on non-communicable diseases

Risk factors are linked to an increased rate of a disease. They can be aspects of a person's lifestyle, or substances in the person's body or environment. A causal mechanism has been proven for some risk factors, but not for others — and many diseases are caused by the interaction of a number of factors.

That sentence is the examiner's favourite trap. A risk factor being linked to a disease does not by itself show it causes it; a causal mechanism has to be demonstrated separately.

Figure: The risk factors named in the specification

Risk factor	Disease it raises the risk of	Mechanism
Diet, smoking and lack of exercise	Cardiovascular disease	Fatty deposits narrow the arteries, reducing blood flow to the heart
Obesity	Type 2 diabetes	Cells respond less well to insulin, so blood glucose stays high
Alcohol	Liver disease, and effects on brain function	The liver breaks down alcohol and is damaged in doing so
Smoking	Lung disease and lung cancer	Chemicals in smoke damage the airways, and carcinogens in tar cause cancer
Smoking and alcohol in pregnancy	Harm to unborn babies	Substances cross the placenta and affect development
Carcinogens, including ionising radiation	Cancer	Damage to DNA leads to uncontrolled cell division

You are also asked to discuss the human and financial cost of these non-communicable diseases — to an individual, a local community, a nation or globally — and to explain the effect of lifestyle factors including diet, alcohol and smoking on their incidence at each of those levels.

Human cost is the illness and shortened life of the patient and the strain on the people around them. Financial cost is treatment and care, lost earnings for the individual, and for a country the cost to its health service plus the working days lost. A good answer names the level it is talking about rather than treating cost as one undifferentiated thing.

The table below does one risk factor at all four levels. In an exam you are usually given the data and asked to interpret it, so the skill is naming which level you are talking about and keeping human cost and financial cost apart.

Figure: One risk factor at four levels: smoking

Level	Human cost	Financial cost
An individual	Breathlessness, higher risk of lung cancer and heart disease, years of life lost	The price of cigarettes, lost earnings during illness, earlier loss of income
A local community	More people ill at the same time; families caring for relatives	Local GP surgeries and hospitals treating more smoking-related illness
A nation	One of the largest single causes of preventable death	Health service spending on treatment, plus working days lost to illness
Globally	The World Health Organization attributes over 8 million deaths a year to tobacco	Treatment costs and lost productivity in every country, heaviest where smoking rates are rising

Worked example

In a study, 20 out of 500 non-smokers and 60 out of 400 smokers developed a lung condition. Compare the incidence, and say what the data does and does not show.

Non-smokers: 20 ÷ 500 = 0.04, which is 4%.
Smokers: 60 ÷ 400 = 0.15, which is 15%.
Compare: 15 ÷ 4 = 3.75.

Answer: The incidence is about 3.75 times higher in smokers. The data shows a correlation between smoking and the condition; on its own it does not prove smoking caused it, though a causal mechanism for smoking and lung disease has been established separately.

Common mistake

Do not write that a study "proves" a risk factor causes a disease. Data from a study shows a correlation. Cause is established by identifying a mechanism — which, for smoking and lung cancer, has been done.

Risk factor: an aspect of a person's lifestyle, or a substance in their body or environment, that is linked to an increased rate of a disease
Causal mechanism: a demonstrated explanation of how one factor brings about a disease; a risk factor is only shown to cause a disease when a causal mechanism has been proven

5.25Coronary heart disease

In coronary heart disease, layers of fatty material build up inside the coronary arteries, narrowing them. This reduces the flow of blood through the coronary arteries, resulting in a lack of oxygen for the heart muscle.

The chain matters: narrowed artery → less blood → less oxygen → less respiration in the heart muscle. Questions ask for the steps, not just the outcome.

Stents are used to keep the coronary arteries open. Statins are widely used to reduce blood cholesterol levels, which slows down the rate of fatty material deposit.

In some people heart valves may become faulty, preventing the valve from opening fully, or the valve might develop a leak. A valve that will not open fully restricts blood flow; one that leaks lets blood flow backwards, so the heart works harder to move the same amount. Faulty heart valves can be replaced using biological or mechanical valves.

In the case of heart failure, a donor heart, or heart and lungs, can be transplanted. Artificial hearts are occasionally used to keep patients alive while waiting for a transplant, or to allow the heart to rest as an aid to recovery.

Figure: Treatments compared — the evaluation the exam asks for

Treatment	Advantages	Disadvantages
Stent	Effective for a long time; surgery is relatively minor and recovery is quick	Risk of infection or of a blood clot forming near the stent; does not treat the underlying cause
Statins	Reduce cholesterol, slowing fatty deposits; also reduce the risk of stroke	Must be taken for life; side effects such as headaches or muscle pain; do not act immediately
Replacement valve	Restores normal flow; biological valves need no lifelong drugs	Major surgery with its own risks; mechanical valves need drugs to prevent clots; biological valves wear out
Heart transplant	Can be a long-term cure	Donor hearts are scarce; risk of rejection; major surgery and lifelong drugs
Artificial heart	Keeps a patient alive while waiting, or lets the heart rest and recover	Less reliable than a donor heart; risk of clotting, so blood-thinning drugs are needed

Common mistake

"Evaluate" means weigh both sides of a method of treatment, bearing in mind its benefits and its risks, and then come to a conclusion. Listing three advantages is half an answer. Say which treatment you would choose for the patient described and why — the judgement is what the last mark is for.

Coronary heart disease: a disease in which layers of fatty material build up inside the coronary arteries, narrowing them and reducing the flow of blood, resulting in a lack of oxygen for the heart muscle
Stent: a device used to keep a coronary artery open so blood can flow through it
Statin: a drug widely used to reduce blood cholesterol levels, which slows down the rate at which fatty material is deposited in the arteries

Before you practise

Name the risk factors and the disease each is linked to — smoking and lung disease, obesity and type 2 diabetes, alcohol and liver damage.
A risk factor makes a disease more likely; it does not guarantee it, and a correlation on its own does not prove cause.
Non-communicable disease has costs beyond the patient: to families, to the health service and to the national economy.
Stents hold an artery open and act quickly, but do not treat the underlying disease.
Statins lower blood cholesterol and slow the disease, but must be taken for life and have side effects.
A replacement or artificial heart, or a bypass, is major surgery with a risk of rejection or clotting.
Lifestyle change is the cheapest treatment and the hardest to sustain — say both.

5.23–5.24The effect of lifestyle on non-communicable diseases

5.25Coronary heart disease

Before you practise

Now practise it