Non-Communicable Disease and What Counts as a Risk Factor
Non-communicable diseases are not passed from person to person. Risk factors are linked to a higher chance of disease, not a guarantee. Some contribute to causing disease; others are markers. Compare correlation with evidence about causes and mechanisms, and distinguish benign from malignant tumours.
What a learner can do afterwards
- Explain what a risk factor is and why it does not guarantee the disease
- Give a case where a mechanism is known and a case where only a correlation has been shown
- Describe how uncontrolled cell division becomes a tumour and distinguish benign from malignant
1 · Read
Non-communicable diseases do not pass between people. Risk factors are features or exposures linked to higher disease risk, not certainty. Some help cause disease; others are markers. DNA carries genetic instructions; genes are sections of DNA. Inherited gene variants are gene differences passed from parents. Smoking, inherited variants and certain infections can raise cancer risk. Infections may spread between people; the resulting cancer is not caught from another person.
You have met correlation before: two things are associated, but that alone does not establish cause. A survey linking a food with more disease shows an association; other factors could explain it. A mechanism explains how an effect happens. Scientists weigh several kinds of evidence. A plausible mechanism alone is not proof, and an unknown mechanism does not rule out a causal link.
Tobacco smoke chemicals can damage DNA. Changes disrupting cell-division controls can contribute to cancer. This is one biological pathway linking smoking to cancer. Smoking causes lung cancer and is a risk factor, but not every smoker develops it. Evidence beyond this pathway supports the causal conclusion.
Cells normally have controls that limit division. If these break down, abnormal cells may keep multiplying and form a tumour. Benign tumours do not invade nearby tissue or spread elsewhere, though they can cause harm by pressing on organs. Malignant tumours are cancerous: they can invade nearby tissue and may spread to distant sites. They need not have spread already to be malignant. Some cancers, such as leukaemia, do not form solid tumours.
Reducing a causal risk factor can lower disease risk without removing it. Stopping smoking lowers future lung cancer risk, but cannot promise that cancer will never occur. Changing an associated marker may not reduce disease if the marker is not a cause. Some risk factors, such as age or inherited variants, cannot be changed. Prevention decisions need evidence about likely benefits and harms.
Risk factors indicate higher chance, not certainty. Correlation alone does not establish cause. Benign tumours do not invade or spread; malignant tumours can.
Lesson, questions and flashcards written for this dataset, with factual background from OpenStax.
Readings and flashcards written for this dataset, with factual background from OpenStax.
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Growth, invasion and spread
A tumour can form when abnormal cells continue multiplying instead of staying under normal division controls. Whether a tumour is benign or malignant depends on its behaviour, not on a protective wrapper.
Benign tumours do not invade surrounding tissue or spread to distant sites. They can still cause harm, for example by pressing on nearby structures. Malignant tumours are cancerous. They can invade nearby tissue and may spread elsewhere. An invading tumour does not become benign because tests find no distant spread. Some cancers, including leukaemia, do not form solid tumours.
Higher chance does not mean certainty
A risk factor identifies a feature or exposure linked to a greater chance of disease. That link does not tell you that every exposed person will become ill. It also does not, by itself, tell you whether the factor causes disease.
Smoking is a causal risk factor for lung cancer. Tobacco smoke chemicals can damage DNA, and changes affecting cell division can contribute to cancer. Other influences matter too, so the outcome is not certain. Inherited variants can also raise risk. Certain infections increase cancer risk, but the resulting cancer is not passed from person to person.
What a study has actually shown
Imagine a survey finding more disease among people who eat a particular food. The survey has found an association. It has not, from that observation alone, established that the food causes the disease.
Another factor might affect both food choices and health. Scientists examine the design of the study and other evidence to distinguish possible explanations. A mechanism can help explain how an effect happens. However, a convincing-sounding pathway is not enough by itself to establish cause. Scientists may also have evidence of a causal effect before the full mechanism is known.
What prevention can promise
Prevention can reduce risk without making disease impossible. Stopping smoking lowers future lung cancer risk, but a person may still develop cancer. A prevention programme should not promise certainty about each person's future.
Some risk factors, such as age or inherited variants, cannot be changed. Other measured features may be markers of disease risk rather than causes. Changing a marker alone may not change the disease outcome. Decisions about prevention need evidence about the action's likely benefits and harms, not an association alone.
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