Animal Tissues, Organs and Systems » Lifestyle and Non-Communicable Diseases

Risk factors

Some people get a non-communicable disease and others do not. Scientists look for things that make a disease more likely. These are called risk factors.

Key terms:

• Risk factor: something that is linked to an increased rate of a disease.
• Causal mechanism: the proven way in which a risk factor leads to a disease.

Risk factors can be:

• aspects of a person's lifestyle, such as what they eat, whether they smoke and how much exercise they take
• substances in the person's body or environment, such as alcohol in the blood or radiation in the surroundings

Having a risk factor does not mean you will definitely get the disease. It means your chance of getting it is higher.

Proven and unproven links

A link between a risk factor and a disease is not the same as proof. For some risk factors, scientists have found a causal mechanism: they know how the risk factor leads to the disease. For others, they have only found that the two go together. The examples below are ones where the effects are well understood.

Diet, smoking and exercise: cardiovascular disease

Cardiovascular disease is disease of the heart and blood vessels. Three lifestyle factors affect it.

How doctors treat heart disease is covered in Coronary Heart Disease and Its Treatments.

Obesity and Type 2 diabetes

Obesity means having a very high amount of body fat. It is a risk factor for Type 2 diabetes, a disease where blood glucose is not controlled properly. People who are obese are more likely to develop it than people of a healthy body mass. Treatment is covered in Diabetes.

Alcohol: liver and brain

Alcohol is a substance that enters the blood. The liver breaks it down, so heavy drinking over many years can damage the liver. Alcohol also affects the brain. It slows down the nervous system, so reactions become slower and judgement is poorer. Long-term heavy drinking can damage brain function.

Smoking: lung disease and lung cancer

Tobacco smoke contains tar and other harmful chemicals. Smoking damages the lungs and airways and causes lung diseases. Smoke also contains chemicals that cause cancer, so smoking is a major risk factor for lung cancer.

Smoking, alcohol and unborn babies

Substances in a pregnant woman's blood can pass to the unborn baby.

• Smoking: increases the risk of problems such as premature birth and a low birth mass.
• Alcohol: can harm the development of the baby, including its brain.

This is why pregnant women are advised not to smoke or drink alcohol.

Carcinogens and ionising radiation

A carcinogen is a substance that can cause cancer. Chemicals in tobacco smoke are carcinogens. So is ionising radiation, such as X-rays, gamma rays and ultraviolet light from the Sun. These are risk factors for cancer because they can damage the genetic material in cells. What happens when cells become cancerous is covered in Cancer.

Key terms:

• Carcinogen: a substance that can cause cancer.
• Ionising radiation: radiation, such as X-rays and gamma rays, that can damage cells and cause cancer.

Many causes working together

Most non-communicable diseases are not caused by one thing. Many diseases are caused by the interaction of a number of factors. For example, the risk of cardiovascular disease depends on diet, smoking and exercise all at the same time. This is why one risk factor on its own rarely tells you who will get a disease.

The cost of non-communicable diseases

These diseases have costs at every level.

• An individual: pain, loss of independence, a shorter life and loss of income if they cannot work.
• A local community: families caring for ill relatives, and local health services stretched by demand.
• A nation: the cost of hospitals, drugs and staff, and lost output when people cannot work.
• The world: non-communicable diseases are common in many countries, so the costs of treatment and lost work add up globally.

The incidence of a disease is the number of new cases in a population. It can be compared in a town, in a country and across the world. Where more people smoke, eat a high-fat diet or drink heavily, more people tend to get the diseases linked to those lifestyle factors. For example, obesity is becoming more common in many countries, so more people are at risk of Type 2 diabetes nationally and globally.

Interpreting risk factor data

Scientists find risk factors by collecting data from people. You should be able to:

• take information from tables, charts and graphs and say what it shows about a risk factor
• turn information from a graph into numbers, and from numbers into a graph
• use a scatter diagram to spot a correlation between a risk factor and a disease

Exam-style question

A study followed 2000 adults. The number of people with cardiovascular disease was recorded for those who took regular exercise and for those who did not.

• Regular exercise: 1000 people, 50 with the disease
• No regular exercise: 1000 people, 150 with the disease

(a) Name one risk factor for cardiovascular disease other than lack of exercise. [1 mark]

(b) What do the results suggest about exercise and cardiovascular disease? [2 marks]

(c) Give one reason why a doctor should be careful when deciding that lack of exercise causes the disease. [1 mark]