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Not every disease can be caught. Non-communicable diseases (NCDs) are not caused by pathogens and cannot be passed on; instead they develop over time, often in response to the way we live. This lesson examines the risk factors for NCDs and the vital distinction between correlation and cause, the effects of diet, exercise, smoking and alcohol, how cardiovascular disease is treated, and an outline of cancer. These are among the biggest causes of ill health in the developed world, so the biology here matters to everyone.
By the end of this lesson you should be able to explain what a risk factor is and distinguish correlation from cause, describe how diet, exercise, smoking and alcohol affect health, compare the treatments for cardiovascular disease, and outline what cancer is and its risk factors.
A risk factor is anything that increases the chance of getting a disease. It does not guarantee the disease — it makes it more likely. Risk factors may be aspects of lifestyle (diet, exercise, smoking, alcohol) or substances in the body or environment (such as carcinogens). Some risk factors are linked to more than one disease.
The most important reasoning skill in this topic is telling apart correlation and cause:
A correlation on its own does not prove cause — there could be a third factor involved, or the link could be coincidence. Scientists become confident that a risk factor causes a disease only when there is a clear correlation, a sensible biological mechanism that explains it, and the link shows up repeatedly in many studies. For smoking and lung cancer, all of these are now established.
Exam Tip: "A graph shows X is linked to disease Y. Does this prove X causes Y?" The expected answer is no — correlation does not prove cause; you also need a biological mechanism and the result to be repeated. This reasoning earns marks across the whole of B6.
| Factor | Effect on health |
|---|---|
| Diet | A poor diet (too much fat, sugar or salt; too little fibre, fruit and vegetables) raises the risk of obesity, type 2 diabetes, cardiovascular disease and some cancers. Too few nutrients weakens the body |
| Lack of exercise | Increases the risk of becoming overweight, which is linked to type 2 diabetes and cardiovascular disease |
| Smoking | Damages the lungs and airways (linked to lung cancer and lung disease) and the heart and blood vessels (cardiovascular disease); in pregnancy it harms the developing baby |
| Alcohol | Excess alcohol damages the liver (cirrhosis) and the brain; in pregnancy it harms the developing baby |
A useful idea is obesity as a shared risk factor: a poor diet and lack of exercise can lead to obesity, which in turn raises the risk of type 2 diabetes and cardiovascular disease. Several lifestyle factors therefore feed into the same diseases, which is why improving lifestyle can reduce risk on several fronts at once.
Cardiovascular disease is disease of the heart and blood vessels. A common form is coronary heart disease, in which the coronary arteries that supply the heart muscle become narrowed by a build-up of fatty material. This reduces the blood flow to the heart muscle, so it receives less oxygen — which can cause chest pain and, if an artery becomes blocked, a heart attack.
There are several ways to treat or manage cardiovascular disease, and OCR expects you to be able to compare them, including weighing them against surgery and transplant.
| Treatment | What it involves | Advantages | Disadvantages |
|---|---|---|---|
| Lifestyle change | Healthier diet, more exercise, stopping smoking | No surgery; cheap; benefits whole-body health; no operation risk | Relies on the person changing habits; works slowly; may not be enough alone |
| Statins | Drugs taken regularly to lower cholesterol in the blood, slowing fatty build-up | Reduce the risk of fatty deposits and heart attack; widely used | Must be taken long term; can have side effects; treat the risk, not an existing blockage |
| Stents | A tube inserted to hold a narrowed artery open, restoring blood flow | Keep the artery open; effective for a specific narrowed vessel; relatively quick procedure | Involves a surgical procedure with some risk; the artery can narrow again over time |
| Surgery / heart transplant | Replacing a severely diseased heart (or major surgery such as a bypass) | Can be life-saving when the heart is failing badly | Major operation with serious risks; donor hearts are scarce; risk of rejection; long recovery |
The general principle examiners look for is that treatments range from the least invasive and cheapest (lifestyle change, then statins) up to the most invasive and risky (stents, then surgery and transplant). Less drastic treatments are usually tried first.
Exam Tip: When comparing treatments, give a balanced answer — at least one advantage and one disadvantage for each. A common high-value point is that a transplant carries the greatest risk and depends on a scarce donor organ, whereas lifestyle change is the least invasive but relies on the patient.
Cancer results from changes to cells that lead to uncontrolled cell division. Normally cell division is carefully controlled; in cancer, cells divide again and again to form a tumour (a mass of abnormal cells). There are two kinds of tumour:
| Type of tumour | Behaviour |
|---|---|
| Benign | The abnormal cells stay in one place (often inside a membrane) and do not invade other tissues; usually not dangerous unless they press on an organ |
| Malignant | The cells invade neighbouring tissues and can spread to other parts of the body in the blood, forming secondary tumours. Malignant tumours are cancers |
Cancer can be caused by both genetic and lifestyle factors:
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