📖 In-Depth Theory
Defining Health
The World Health Organisation (WHO) defines health as:
'A state of complete physical, mental and social wellbeing — not merely the absence of disease or infirmity.'
This definition is important because it highlights that health is about more than just not being ill. A person can be free of physical disease but still be unhealthy if they have poor mental health or are isolated from society.
Good health requires:
Physical wellbeing — the body functions properly, free from disease.
Mental wellbeing — good emotional and psychological state.
Social wellbeing — positive relationships and a functioning role in society.
Types of Disease
A disease is a condition that impairs the normal functioning of the body.
COMMUNICABLE DISEASES (infectious):
Caused by pathogens — bacteria, viruses, fungi, protists.
Can be spread from one organism to another.
Examples: influenza, HIV, tuberculosis (TB), measles, malaria, salmonella food poisoning.
NON-COMMUNICABLE DISEASES (non-infectious):
Cannot be spread from person to person.
Typically caused by genetic factors, lifestyle choices or environmental exposure.
Examples: coronary heart disease, type 2 diabetes, most cancers, asthma.
Interactions between diseases: having one disease can affect the risk of developing another. For example:
HIV weakens the immune system → patient more vulnerable to other infections.
Cancer treatment (chemotherapy) suppresses immunity → risk of other infections increases.
Diabetes increases risk of cardiovascular disease.
Risk Factors
A risk factor is anything that increases the probability of developing a disease — but does NOT guarantee it.
There is an important distinction:
CORRELATION — a statistical link between a risk factor and a disease.
CAUSATION — evidence that the risk factor directly CAUSES the disease.
Many risk factors show strong correlation with disease AND have been shown to cause disease through scientific study (e.g. smoking and lung cancer).
Others show correlation but causation is harder to prove.
Risk factors can be:
LIFESTYLE FACTORS (choices): smoking, diet, alcohol consumption, physical inactivity.
ENVIRONMENTAL FACTORS: air pollution, UV radiation, exposure to chemicals or asbestos.
GENETIC FACTORS: inherited predispositions to certain diseases.
Non-Communicable Disease and Lifestyle
Non-communicable diseases are increasingly common in wealthy countries — often linked to lifestyle choices.
Key links between lifestyle and non-communicable disease:
SMOKING:
Strongly linked to lung cancer, mouth cancer, throat cancer, bladder cancer.
Also linked to coronary heart disease and chronic obstructive pulmonary disease (COPD).
ALCOHOL:
Excessive alcohol linked to liver disease (cirrhosis), liver cancer, mouth cancer, brain damage.
Increases risk of accidents and mental health problems.
POOR DIET:
High saturated fat diet → high cholesterol → increased CHD risk.
High sugar diet → type 2 diabetes, obesity.
Low fibre diet → increased bowel cancer risk.
LACK OF EXERCISE:
Increases risk of obesity, CHD, type 2 diabetes, some cancers.
OBESITY (BMI > 30):
Strongly linked to type 2 diabetes, CHD, high blood pressure, some cancers.
UV RADIATION (from sunlight/sunbeds):
Causes skin cancer (including melanoma — the most dangerous type).
⚠️ Common Mistake
A risk factor INCREASES the probability of getting a disease — it does NOT mean you WILL get it. A non-smoker can develop lung cancer; a heavy smoker might not. Risk factors change the statistical likelihood, not the certainty. Also — correlation does NOT always mean causation, though for many lifestyle risk factors, both have been established.