The effect of lifestyle on some non-communicable diseases: Many diseases are caused by the interaction of a number of factors.

The idea

Most non-communicable diseases, such as cardiovascular disease, type 2 diabetes, some cancers and chronic respiratory disease, do not have a single cause. They arise from interactions between several factors: genetic inheritance, lifestyle choices such as diet, smoking, alcohol and exercise, and environmental influences such as air pollution or exposure to carcinogens. These factors can combine, and their effects may be additive or multiplicative. For example, a person who smokes, has a high-saturated-fat diet and has a family history of heart disease may face a much greater risk than someone with only one of these factors. Because risk factors interact, it is often impossible to identify one cause, and reducing several risk factors together can lower risk more than changing just one.

What earns the marks

• States that many diseases have multiple contributing factors rather than a single cause.
• Identifies categories of factors, such as genetic, lifestyle and environmental influences.
• Gives a named disease and at least two interacting factors, for example heart disease with smoking and a high-saturated-fat diet.
• Explains that factors can interact so their combined effect on risk is greater than either factor alone.
• Uses the idea of risk to explain that having several factors increases the probability of disease without making it certain.
• Suggests that reducing more than one risk factor can lower the chance of developing the disease.

Common mistakes and how to put them right

• Claiming that one factor alone always causes a named disease.

  Put it right: Many diseases result from several interacting factors, and a single factor usually changes risk rather than determining outcome.

• Treating correlation as proof of causation.

  Put it right: An observed association suggests a risk factor but does not by itself prove that the factor causes the disease.

• Assuming that genetic factors cannot be influenced at all.

  Put it right: Genetic risk may be fixed, but lifestyle changes can still reduce overall risk.

Exam tips

• Use a named disease and two or three specific factors, then explain how they combine to increase risk.
• Include the word interaction to show that factors work together rather than in isolation.
• Avoid absolute language such as always or never; use terms such as increases the risk or makes it more likely.