Health and non-communicable disease

Health is a state of physical and mental well-being. Diseases are a major cause of ill health. Communicable diseases are caused by pathogens and can spread; non-communicable diseases, such as heart disease, most cancers and Type 2 diabetes, cannot. Many of them are linked to risk factors in the way we live.

Key facts

  • Communicable diseases are caused by pathogens and can be passed on. Non-communicable diseases are not caused by pathogens and cannot be passed from person to person.
  • A risk factor makes a disease more likely: smoking (lung disease, lung cancer, heart disease), obesity and too little exercise (Type 2 diabetes, heart disease), alcohol (liver disease), ultraviolet light and other carcinogens (cancer).
  • A correlation between a risk factor and a disease does not on its own prove cause. Scientists look for a mechanism, such as chemicals in tobacco smoke damaging DNA.
  • Cancer is the result of changes in cells that lead to uncontrolled growth and division. Benign tumours stay in one place; malignant tumours are cancers that invade tissues and spread in the blood to form secondary tumours.
  • In coronary heart disease, layers of fatty material build up inside the coronary arteries, so less oxygen reaches the heart muscle. Treatments: stents keep arteries open, statins lower blood cholesterol, and failing hearts or valves can be replaced.
  • Diseases interact: a weak immune system makes infection more likely, some viruses trigger cancers, and ill health can affect mental health.
  • Health data: percentage = part ÷ whole × 100; rate per 100,000 = cases ÷ population × 100,000; BMI = mass (kg) ÷ height² (m²).

Worked examples

Example 1

A person has a mass of 72 kg and a height of 1.80 m. Calculate their BMI and say which category they are in.

  1. Square the height. 1.80² = 3.24
  2. Divide the mass by it. 72 ÷ 3.24 = 22.2
  3. 18.5 to 24.9 is a healthy weight, so this person is a healthy weight.

Answer: 22.2 kg/m², a healthy weight

Example 2

A town of 40,000 people had 18 new cases of a cancer in a year. How many cases is that per 100,000 people?

  1. Divide the cases by the population, then multiply by 100,000. 18 ÷ 40000 × 100000 = 45
  2. Rates per 100,000 let us compare places with different populations.

Answer: 45

Example 3

Explain how coronary heart disease damages the heart, and how a stent helps.

  1. The coronary arteries supply the heart muscle with blood.
  2. Fatty material builds up inside them and narrows them.
  3. Less blood, so less oxygen, reaches the heart muscle, which can cause a heart attack.
  4. A stent is a mesh tube put inside the artery to hold it open.

Answer: fatty material narrows the coronary arteries, so the heart muscle gets less oxygen; a stent holds the artery open so blood can flow

Example 4

Data show that people who smoke are much more likely to develop lung cancer. Does this prove that smoking causes lung cancer?

  1. The data show a correlation: more smoking goes with more lung cancer.
  2. A correlation could be caused by a third factor or by chance.
  3. Scientists found the mechanism: carcinogens in tobacco smoke cause mutations in lung cells.
  4. With a mechanism and repeated studies, smoking is accepted as a cause.

Answer: the correlation alone does not, but together with the mechanism (carcinogens in smoke damage DNA) the evidence shows that smoking causes it