13.15 - 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 and searching 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.
• To decide whether a risk factor is a cause, scientists look for a plausible mechanism that explains how it could bring the disease about, not just a statistical link.

Example - Lifestyle and cardiovascular disease

• A lack of exercise and a high-fat diet are strongly linked to cardiovascular disease, but they do not cause it directly.
• It is the high blood pressure and high level of "bad" cholesterol they lead to that actually damage the arteries.

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.

Obesity

• Obesity means carrying so much body fat that it poses a risk to health.
• It develops when a person regularly takes in more energy from food than they use up.
• This is often caused by a diet high in fat and sugar combined with too little exercise.
• The excess energy is stored as fat, and over time this leads to obesity.

Obesity is itself a risk factor for other non-communicable diseases

• Type 2 diabetes - Obesity is thought to cause it. Being obese makes the body's cells less sensitive (more resistant) to insulin, so the body struggles to control the concentration of glucose in the blood.
• Cardiovascular disease - Obesity raises the risk of it.

Because these diseases are closely linked, a person who is obese often goes on to suffer from more than one of them.