Risk Factors and Lifestyle Effects on Health (Part 2/2) Revision Notes | GCSE Edexcel Higher Biology

1. The Evidence Problem - Proven vs Suspected

Here's the challenge: some risk factors have rock-solid proof of how they cause disease, while others just show up together with disease in the data. The difference matters for your exams and for real medicine.

Think of smoking and lung cancer. We don't just know they're linked - we know exactly how tar damages lung cells, triggers mutations, and leads to tumours. That's a proven causal mechanism.

But what about stress and heart disease? People with high stress do get more heart attacks, but we can't prove stress directly damages heart muscle. The mechanism isn't fully understood yet.

2. Examples of Proven Causal Mechanisms

Let's look at risk factors where scientists have cracked the code - they know exactly what's happening inside your body.

Smoking → Lung cancer: Tar contains over 70 carcinogens. These chemicals bind to DNA in lung cells, causing mutations. Mutated cells divide uncontrollably, forming tumours. We can trace every step.

High blood pressure → Stroke: Excessive pressure damages artery walls. Damaged areas attract blood clots. If a clot blocks a brain artery, brain tissue dies. Clear cause and effect.

UV radiation → Skin cancer: UV rays damage DNA in skin cells. The cell's repair mechanisms can't keep up. Damaged cells become cancerous and multiply rapidly.

3. When We Only Have Correlation

Many risk factors show strong statistical links to disease, but we haven't figured out the biological mechanism yet. This doesn't make them less important - just less understood.

Stress and heart disease: Highly stressed people get more heart attacks. But does stress directly damage the heart? Or does it make people smoke more, eat badly, and exercise less? The pathway isn't clear.

Social deprivation and illness: Poor areas have higher disease rates. Is it the stress of poverty? Poor diet? Less healthcare access? Probably all three, but we can't separate them easily.

Trap: Many students think correlation means the link is weak or unimportant. Actually, some correlations are incredibly strong - we just don't understand the mechanism yet.

4. Multiple Factors Working Together

Here's where it gets complex: most diseases aren't caused by one thing. They're caused by multiple risk factors combining and amplifying each other's effects.

Think of heart disease. It's not just high blood pressure OR smoking OR poor diet. It's the combination that's deadly. Each factor makes the others worse.

Worked example: How Multiple Factors Combine - Heart Disease Example

A 45-year-old person smokes 20 cigarettes daily, has high blood pressure, and eats a high-fat diet. Explain how these factors interact.

1. Smoking damages artery walls High BP puts extra pressure on arteries High-fat diet increases cholesterol — Each factor causes damage on its own
2. Damaged arteries (smoking) + high pressure = faster artery damage Cholesterol deposits stick to damaged walls more easily — Factors multiply each other's effects
3. Severely narrowed arteries + high pressure + blood clots — Risk is much higher than adding individual risks
4. Heart attack or stroke becomes highly likely — Multiple factors create a 'perfect storm'

Answer: The three factors interact synergistically - each makes the others more dangerous, creating exponentially higher risk than any single factor alone.

This interaction explains why some people smoke for decades without getting lung cancer, while others develop it quickly. It's not just smoking - it's smoking plus genetics plus other environmental factors plus immune system strength.

5. Exam Technique - Evaluating Evidence

Exam questions love testing whether you can distinguish between proven causation and correlation. Here's how to tackle them like a pro.

Exam depth extension: In risk factors and lifestyle effects on health (part 2/2), connect the evidence problem - proven vs suspected to examples of proven causal mechanisms using clear cause-and-effect statements. When you explain biological processes, include what changes, why it changes, and the consequence for cells, organisms, or populations. If calculations appear, show each step, include units, and end with a sentence that interprets the result in biological context.

Command word alert: 'Evaluate' questions want you to weigh up evidence. Discuss what we know for certain (proven mechanisms) versus what we suspect (correlations), then reach a balanced conclusion.

Common mistake: Students often write 'smoking causes lung cancer' without explaining the mechanism. In evaluation questions, you need to show you understand how we know this - what's the biological pathway?