Non-communicable Disease Usually Has Several Causes
Definition
Risk factor
Something that increases the chance of getting a disease, such as smoking, a poor diet or lack of exercise.
- A risk factor increases the probability of disease but does not guarantee that disease will develop.
- Age, inherited alleles, lifestyle and environmental exposure can interact in one person.
Key Idea
Risk is cumulative because several factors can affect the same tissue or biological process.
Cardiovascular Disease Has Interacting Risks
- Smoking damages artery linings, high blood pressure increases mechanical stress, and a diet high in saturated fat can raise blood cholesterol.
- These factors promote fatty deposits and blood clots, reducing blood flow to the heart or brain.
- Exercise, diet, age and inherited alleles modify the overall risk.
- Fatty deposits narrow arteries, damaged endothelium encourages clot formation and high blood pressure increases stress on vessel walls.
Cancer Risk Depends on Mutation and Exposure
- Cancer develops when mutations disrupt control of cell division.
- Tobacco smoke, ionising radiation and some infections increase mutation risk, while inherited alleles can reduce DNA repair or cell-cycle control.
- Longer exposure and increasing age allow more mutations to accumulate.
- Cancer risk increases as mutations accumulate in genes controlling cell division, DNA repair and programmed cell death.
Lung, Liver and Nutritional Diseases Have Multiple Factors
- Smoking, air pollution and occupational dust can combine to damage lungs.
- Heavy alcohol intake, viral infection and obesity can combine to damage the liver.
- Diet, physical activity, income, access to food and inherited metabolism influence obesity, malnutrition and type 2 diabetes.
- Smoke particles damage alveoli and cilia, while carbon monoxide and nicotine add cardiovascular strain, so one exposure contributes to several diseases.
- Alcohol metabolism can produce toxic compounds, fatty liver and inflammation before scar tissue reduces liver function.
Example
smoking and high blood pressure both damage arteries, so a person exposed to both may have a greater cardiovascular risk than a person exposed to either factor alone.
Correlation Does Not Prove Causation
Definition
Correlation
A link between two things, where a change in one is matched by a change in the other, without proving that one causes the other.
- A correlation is an association between variables, while causation means one factor produces a change in the other.
- Confounding variables, reverse causation and chance can produce a correlation without direct causation.
- Shared variables such as age, income or diet can confound a correlation, so controlled evidence and a plausible mechanism are needed for causation.
Exam technique
- When interpreting data, describe the trend, use figures if provided, then state why the pattern alone cannot prove cause.
- A mechanism and evidence from controlled studies strengthen a causal conclusion.
Evaluate Risk in Context
- Relative risk compares probabilities between groups, while absolute risk shows the actual chance of disease.
- A small absolute risk can appear dramatic when only relative change is reported.
Self review
- What is a risk factor?
- How can factors interact in cardiovascular disease?
- Give three influences on cancer risk.
- Why does correlation not prove causation?
