5.4.1 Interaction of factors in non-communicable disease

Non-communicable Disease Usually Has Several Causes

1. A risk factor increases the probability of disease but does not guarantee that disease will develop.
2. Age, inherited alleles, lifestyle and environmental exposure can interact in one person.

Cardiovascular Disease Has Interacting Risks

1. Smoking damages artery linings, high blood pressure increases mechanical stress, and a diet high in saturated fat can raise blood cholesterol.
2. These factors promote fatty deposits and blood clots, reducing blood flow to the heart or brain.
3. Exercise, diet, age and inherited alleles modify the overall risk.
4. Fatty deposits narrow arteries, damaged endothelium encourages clot formation and high blood pressure increases stress on vessel walls.

Cancer Risk Depends on Mutation and Exposure

1. Cancer develops when mutations disrupt control of cell division.
2. Tobacco smoke, ionising radiation and some infections increase mutation risk, while inherited alleles can reduce DNA repair or cell-cycle control.
3. Longer exposure and increasing age allow more mutations to accumulate.
4. Cancer risk increases as mutations accumulate in genes controlling cell division, DNA repair and programmed cell death.

Lung, Liver and Nutritional Diseases Have Multiple Factors

1. Smoking, air pollution and occupational dust can combine to damage lungs.
2. Heavy alcohol intake, viral infection and obesity can combine to damage the liver.
3. Diet, physical activity, income, access to food and inherited metabolism influence obesity, malnutrition and type 2 diabetes.
4. Smoke particles damage alveoli and cilia, while carbon monoxide and nicotine add cardiovascular strain, so one exposure contributes to several diseases.
5. Alcohol metabolism can produce toxic compounds, fatty liver and inflammation before scar tissue reduces liver function.

Correlation Does Not Prove Causation

1. A correlation is an association between variables, while causation means one factor produces a change in the other.
2. Confounding variables, reverse causation and chance can produce a correlation without direct causation.
3. Shared variables such as age, income or diet can confound a correlation, so controlled evidence and a plausible mechanism are needed for causation.

Evaluate Risk in Context

1. Relative risk compares probabilities between groups, while absolute risk shows the actual chance of disease.
2. A small absolute risk can appear dramatic when only relative change is reported.

5.4.2 Lifestyle factors and non-communicable disease

Lifestyle Changes Disease Risk at Every Scale

1. Lifestyle factors change exposure to biological risks, while social and economic conditions affect the choices available.
2. Effects can be measured in individuals, local communities, countries and global populations.

Diet and Exercise Affect Body Mass

1. Energy intake above energy use causes fat storage and can lead to obesity, while insufficient energy or nutrients cause malnutrition.
2. Regular exercise raises energy use and improves cardiovascular fitness.
3. Body mass index is calculated using $\mathrm{BMI}=\frac{\mathrm{mass}(\mathrm{kg})}{{\left(\mathrm{height}(\mathrm{m})\right)}^2}$.
4. BMI estimates mass relative to height but cannot distinguish fat from muscle or show where fat is stored.
5. Excess energy intake increases fat storage, while diets deficient in energy, protein or micronutrients cause different forms of malnutrition.
6. Waist-to-hip ratio is calculated using $\mathrm{WHR}=\frac{\mathrm{waist}\mathrm{circumference}}{\mathrm{hip}\mathrm{circumference}}$, with both measurements in the same unit.

Alcohol Damages the Liver

1. The liver metabolises alcohol, and repeated high intake damages liver cells.
2. Fat can accumulate, followed by inflammation and irreversible scarring called cirrhosis.
3. Reducing alcohol intake lowers risk, but established cirrhosis may not be reversible.
4. Alcohol damages hepatocytes, promotes fat accumulation and inflammation, and repeated injury can produce irreversible cirrhosis.

Smoking Raises Cardiovascular Risk

1. Carbon monoxide reduces the oxygen carried by haemoglobin, so the heart works harder to supply tissues.
2. Nicotine raises heart rate and blood pressure, while smoke chemicals damage artery linings and promote fatty deposits and clots.
3. Waist-to-hip ratio estimates central fat distribution, which is associated with greater cardiovascular and type 2 diabetes risk.
4. Smoking damages artery linings, raises blood pressure, reduces oxygen transport and increases the probability of thrombosis.

Local, National and Global Effects

1. Locally, disease patterns reflect food access, income, transport, recreation space and exposure to tobacco or alcohol.
2. Nationally, non-communicable disease increases healthcare costs and reduces productivity.
3. Globally, urbanisation, poverty and unequal healthcare create both obesity and undernutrition in different populations.
4. Population disease patterns reflect food price, advertising, working conditions, healthcare access and public-health policy as well as personal choice.

Interpret Lifestyle Evidence Carefully

1. Self-reported diet, alcohol and smoking data may be inaccurate.
2. Observational data may contain confounding variables, so an association does not prove that one lifestyle factor acted alone.

5.4.3 Treatments for cardiovascular disease

Cardiovascular Treatments Balance Benefit and Risk

1. Treatment choice depends on disease severity, age, other conditions, surgical risk and the person's ability to maintain long-term changes.
2. A treatment plan may combine lifestyle changes, medication and surgery because these approaches act in different ways and can be reviewed as the person's condition changes.

Medication Reduces Future Risk

1. Statins lower blood cholesterol and slow formation of fatty deposits, reducing future heart-attack and stroke risk.
2. Antihypertensive drugs lower blood pressure, while anticoagulants reduce harmful clot formation in selected patients.
3. Medication avoids major surgery but may be lifelong, can cause side effects and depends on regular adherence.
4. Statins inhibit cholesterol production in the liver, lowering blood LDL cholesterol and slowing growth of fatty arterial deposits.

Surgery Restores Blood Flow Quickly

1. A stent is expanded inside a narrowed coronary artery to hold it open and improve blood flow.
2. Coronary bypass surgery uses a graft vessel to route blood around a severe blockage.
3. Surgery can relieve severe restriction rapidly but carries risks from bleeding, infection, anaesthesia and clot formation.
4. A stent immediately widens a narrowed artery but can trigger clot formation, so antiplatelet medication may be required.
5. Bypass surgery restores flow around severe blockages but requires major surgery, anaesthesia and a longer recovery.

Lifestyle Change Reduces Underlying Risk

1. Stopping smoking reduces artery damage and carbon-monoxide exposure.
2. A balanced diet, exercise and weight reduction can lower blood pressure, improve blood lipids and reduce type 2 diabetes risk.
3. Lifestyle change has wider benefits and few medical side effects, but results are gradual and sustained behaviour change can be difficult.
4. Lifestyle changes reduce several underlying risks simultaneously, but benefit develops gradually and depends on sustained adherence.

Combine Treatments When Appropriate

1. A patient may receive emergency surgery for immediate blood flow, medication for future risk and lifestyle support for underlying causes.
2. The best option is individual because one treatment can be unsuitable when another condition changes its risk.
3. Medication controls risk only while it is taken, and side effects or interactions may make one drug unsuitable.
4. A justified treatment plan may combine an urgent procedure with lifelong medication and lifestyle support because the options solve different parts of the problem.

Make a Conditional Judgement

1. Severe obstruction may justify procedural risk because restoring blood flow is urgent.
2. Milder disease may first be managed with medication and lifestyle change, followed by review of the response.