2.10 - Non-Communicable Disease

Non-communicable disease and risk factors

• A non-communicable disease is one that cannot be passed from person to person - it is not caused by a pathogen, so it is not infectious.
• These diseases generally last a long time and get worse slowly.
• Examples include:
  • Cardiovascular disease
  • Many cancers
  • Some lung and liver diseases
  • Type 2 diabetes

Risk factors

• Rather than being caught from someone else, non-communicable diseases are linked to risk factors.
• A risk factor is anything that increases the likelihood that a person will develop a particular disease during their lifetime.
• A risk factor does not guarantee the disease - someone with a risk factor is simply more likely to develop it than someone without it.

Types of risk factor

• Lifestyle - Aspects of how a person lives, such as how much exercise they do, or whether they smoke
• Substances in the environment - Such as air pollution around them
• Substances in the body - Substances found inside the body
• Inherited genes - The genes a person has inherited, which can make them more susceptible to some diseases

Many non-communicable diseases are caused by several of these risk factors interacting, rather than by any single factor on its own.

Correlation and cause

• Scientists identify risk factors by looking at data for correlations - links where two things tend to change together (e.g. more of a certain behaviour found alongside more cases of a disease).
• A correlation on its own does not prove that one thing causes the other.
• For some risk factors a causal mechanism has been proven, so the factor really does cause the disease. For others, the risk factor is only correlated with the disease and the true cause lies elsewhere.

Proving cause needs a mechanism

• To decide whether a risk factor is a cause, scientists look for a plausible mechanism explaining how it could bring the disease about - not just a statistical link.
• Example: a lack of exercise and a high-fat diet are strongly linked to cardiovascular disease, but they don't cause it directly.
• It's the high blood pressure and high level of "bad" cholesterol they lead to that actually damage the arteries.

Showing data on a scatter diagram

• A scatter diagram plots two variables against each other - e.g. a measure of a lifestyle factor against the incidence of a disease - so you can see whether they are correlated and how strongly.
• Disease-incidence figures can also be translated between graphical and numerical forms - for instance reading a value off a graph, or working out a number of cases from a percentage.

The cost of non-communicable disease

• The incidence of a non-communicable disease means the number of new cases.
• Incidence varies between different parts of the world, between regions of one country, and from person to person - because different groups tend to have different risk factors.

Why incidence varies

• Wealthier, developed countries - Higher incomes make it easier to buy energy-rich food and live without much physical activity, so obesity and the diseases it raises are common.
• More deprived areas within a country - People here are more likely to smoke, eat poorly, and exercise less, so cardiovascular disease, obesity, and Type 2 diabetes are more common.
• Individual choices - A person's own choices then affect their personal risk.

Lifestyle risk factors

• A risk factor is an aspect of a person's life or environment linked to an increased chance of developing a disease.
• The four main lifestyle risk factors for non-communicable diseases are diet, exercise, alcohol, and smoking.
• Each is linked to particular diseases, and because these diseases overlap, someone with several risk factors is at much greater risk than someone with one.

Diet

• Eating too much - especially fatty and sugary food - takes in more energy than the body uses, and the excess is stored as fat.
• A poor diet is a risk factor for obesity, and through it for Type 2 diabetes and cardiovascular disease.
• A diet high in saturated fat raises the level of "bad" cholesterol in the blood, which contributes to fatty deposits forming inside arteries - raising cardiovascular risk.
• Too few nutrients causes the opposite problem: malnutrition.

Exercise

• Being active increases the energy the body uses and reduces the fat stored.
• It builds muscle, which raises the metabolic rate so energy from food is used up more quickly.
• People who exercise regularly are less likely to become obese or develop cardiovascular disease.
• A lack of exercise has the reverse effect and raises blood pressure, increasing cardiovascular risk.

Alcohol

• Drinking too much alcohol is a risk factor for liver disease - alcohol is broken down by the liver and some of the products are toxic.
• Drinking heavily over a long period can permanently damage the liver.
• Alcohol is also linked to cardiovascular disease and to some cancers.

Smoking

• Smoking is a major risk factor for cardiovascular disease. The chemicals in cigarette smoke:
  • Raise the heart rate and blood pressure
  • Damage the walls of the arteries, encouraging fatty deposits and blood clots to build up
• This makes a heart attack or stroke more likely.
• Smoking is also a well-established risk factor for lung disease and lung cancer.