Health & Disease

Health issues

Health is the state of physical and mental wellbeing. Disease is a major cause of ill health, but other factors matter too — diet, stress and life situation all affect both physical and mental health.

Diseases fall into two groups. Communicable diseases are caused by pathogens and can be passed between people. Non-communicable diseases cannot be transmitted; they include cancer, coronary heart disease and type 2 diabetes.

Different types of disease can interact:

• Defects in the immune system make a person more likely to suffer from infectious diseases.
• Viruses living in cells can trigger cancers.
• Immune reactions initially caused by a pathogen can trigger allergies such as skin rashes and asthma.
• Severe physical ill health can lead to depression and other mental illness.

Risk factors for non-communicable disease

A risk factor is anything linked to an increased rate of a disease. Risk factors may be aspects of a person's lifestyle or substances in their body or environment.

• Diet, smoking and exercise affect the risk of cardiovascular disease.
• Obesity is a risk factor for type 2 diabetes.
• Alcohol affects the liver and brain function, and drinking in pregnancy affects the unborn baby.
• Smoking affects lung disease and lung cancer, and smoking in pregnancy affects the unborn baby.
• Carcinogens, including ionising radiation, are risk factors for cancer.

Non-communicable diseases carry human and financial costs — to the individual, to their family, and to the health service and wider economy.

Be careful with the language of causation. A correlation between a factor and a disease is not the same as proof that the factor causes it. To show a causal mechanism you need evidence of how the factor produces the effect. Questions frequently reward candidates who spot this distinction and penalise those who over-claim from a graph.

Cancer

Cancer results from changes in cells that lead to uncontrolled growth and division. This forms a tumour.

• Benign tumours are growths of abnormal cells contained in one area, usually within a membrane. They do not invade other parts of the body.
• Malignant tumour cells are cancers. They invade neighbouring tissues and spread to different parts of the body in the blood, where they form secondary tumours.

Both genetic risk factors and lifestyle risk factors contribute to cancer.